text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
An electro-switchable biosurface is a biosensor that is based on an electrode (often gold) to which a layer of biomolecules (often DNA molecules) has been tethered. An alternating or fixed electrical potential is applied to the electrode which causes changes in the structure and position (movement) of the charged biomolecules. The biosensor is used in science, e.g. biomedical and biophysical research or drug discovery, to assess interactions between biomolecules and binding kinetics as well as changes in size or conformation of biomolecules. | 1 | Biochemistry |
In August 1962 the Ministry of Health announced it was forming a poisons information service. This was after the Emergency Treatment in Hospital of Cases of Acute Poisoning published by the Central Health Services Council in March 1962. Many more household chemicals were on the market, and the chemical composition was only known to the manufacturers. 4,000 to 5,000 people each year were lethally poisoned, with 6,085 in 1962; however, many of the deaths were (non-accidental) suicides.
It started in 1963 by Dr Roy Goulding at the Medical Toxicology Unit of Guy's Hospital, with a staff of 65. By the late 1960s, recreational drugs were presenting a widespread danger. Other centres were soon set up in Edinburgh, Belfast and Cardiff.
UKTIS was based in Newcastle from 1995. | 1 | Biochemistry |
The elongation phase starts once assembly of the elongation complex has been completed, and progresses until a termination sequence is encountered. The post-initiation movement of RNA polymerase is the target of another class of important regulatory mechanisms. For example, the transcriptional activator Tat affects elongation rather than initiation during its regulation of HIV transcription. In fact, many eukaryotic genes are regulated by releasing a block to transcription elongation called promoter-proximal pausing. Pausing can influence chromatin structure at promoters to facilitate gene activity and lead to rapid or synchronous transcriptional responses when cells are exposed to an activation signal. Pausing is associated with the binding of two negative elongation factors, DSIF (SPT4/SPT5) and NELF, to the elongation complex. Other factors can also influence the stability and duration of the paused polymerase. Pause release is triggered by the recruitment of the P-TEFb kinase.
Transcription termination has also emerged as an important area of transcriptional regulation. Termination is coupled with the efficient recycling of polymerase. The factors associated with transcription termination can also mediate gene looping and thereby determine the efficiency of re-initiation. | 1 | Biochemistry |
Bisulfite sequencing is used widely across mammalian genomes, however complications have arisen with the discovery of a new mammalian DNA modification 5-hydroxymethylcytosine. 5-Hydroxymethylcytosine converts to cytosine-5-methylsulfonate upon bisulfite treatment, which then reads as a C when sequenced. Therefore, bisulfite sequencing cannot discriminate between 5-methylcytosine and 5-hydroxymethylcytosine. This means that the output from bisulfite sequencing can no longer be defined as solely DNA methylation, as it is the composite of 5-methylcytosine and 5-hydroxymethylcytosine. The development of Tet-assisted oxidative bisulfite sequencing by Chuan He at the University of Chicago is now able to distinguish between the two modifications at single base resolution. | 1 | Biochemistry |
The reaction was originally carried out in diethyl ether and routinely generated high yields due to the inherent irreversibly of the reaction caused by the formation of nitrogen gas. Though these reactions can be carried out at room temperature, the rate does increase at higher temperatures. Typically, the reaction is carried out at less than refluxing temperatures. The optimal reaction temperature is determined by the specific diazoalkane used. Reactions involving diazomethanes with alkyl or aryl substituents are exothermic at or below room temperature. Reactions involving diazomethanes with acyl or aroyl substituents require higher temperatures. The reaction has since been modified to proceed in the presence of Lewis acids and common organic solvents such as THF and dichloromethane. Reactions generally run at room temperature for about an hour, and the yield ranges from 70%-80% based on the choice of Lewis acid and solvent. | 0 | Organic Chemistry |
Researchers prove that in the developing CNS, Nav1.2 is initially expressed at all forming nodes of Ranvier. Upon maturation, nodal Nav1.2 is down-regulated and replaced by Nav1.6. Nav1.2 is also expressed during PNS node formation, which suggests that the switching of Nav-channel subtypes is a general phenomenon in the CNS and PNS. In this same investigation, it was shown that Nav1.6 and Nav1.2 colocalize at many nodes of Ranvier during early myelination. This also led to the suggestion that early clusters of Nav1.2 and Nav1.6 channels are destined to later become nodes of Ranvier. Neurofascin is also reported to be one of the first proteins to accumulate at newly forming nodes of Ranvier. They are also found to provide the nucleation site for attachment of ankyrin G, Nav channels, and other proteins. The recent identification of the Schwann cell microvilli protein gliomedin as the likely binding partner of axonal neurofascin brings forward substantial evidence for the importance of this protein in recruiting Nav channels to the nodes of Ranvier. Furthermore, Lambert et al. and Eshed et al. also indicates that neurofascin accumulates before Nav channels and is likely to have crucial roles in the earliest events associated with node of Ranvier formation. Thus, multiple mechanisms may exist and work synergistically to facilitate clustering of Nav channels at nodes of Ranvier. | 1 | Biochemistry |
In the 2010s, machine learning emerged as a powerful tool for guiding catalyst discovery. More specifically, machine learning models such as multivariate linear regression have been applied to study the linear free energy relationships (LFERs) in catalytic asymmetric organic reactions. These relationships describe the effects that ligand substituents have on reaction outcomes, namely enantioselectivity, and can be extrapolated to predict the performance of ligands outside the known dataset. However, machine learning approaches require well-defined molecular descriptors for the steric and electronic properties of ligands in order to make accurate predictions. Sterimol parameters emerged as a good candidate for quantifying the steric environment induced by ligands.
In Matthew Sigmans seminal work published in 2012, Sterimol parameters were implemented in asymmetric catalysis for the first time in the analysis of an asymmetric Nozaki-Hiyama-Kishi reaction (Figure 2). In initial ligand screening the team found that the steric hindrance of the ester substituent on the oxazoline-proline-based ligand scaffold was pertinent to the overall enantioselectivity of the reaction. When attempting to use the Charton modification of the Tafts parameters for probing the LFERs, they observed breaks in linearity with respect to several "isopropyl-like" substituents with large Charton values (Figure 3, left). However, this break did not exist when the Sterimol B parameter was used instead. All of the substituents studied demonstrated good linear correlation between their Sterimol B value and the reaction enantioselectivity (Figure 3, right).
Sigman attributed the superiority of Sterimol B in this prediction over Charton values to the inherent limitations of the experimentally based Charton values. He noted that the Charton model assumes that the substituent can rapidly rotate around the X-axis. However, in the context of asymmetric catalysis, only one conformation of the substituent provides the transition state with lowest energy, which leads to the formation of the major enantiomer. Therefore, Charton values tend to overestimate the steric effects of substituents that are non-symmetrical around the X-axis, because they can only describe the net conformer of a certain substituent. Sterimol parameters, in contrast, are not derived from experimental results, which are sometimes idiosyncratic as a result of distinct mechanisms. By virtue of their origin, namely quantum chemical calculations, Sterimol parameters can more accurately interpret the steric effects of a substituent in its static form. Sterimol B, in particular, can approximate the steric repulsive effect of the exact conformer with the lowest energy. Table 1 demonstrates the differences of the two parameters. For example, while they have the same Sterimol B values, the Charton value of the isopropyl-like CHPr substituent is significantly larger than that of i-Pr due to overestimation. This explains why better correlation was obtained with Sterimol B.
To date, the Sigman lab has applied Sterimol parameters in the analysis of several catalytic asymmetric reactions. Sterimol parameters are also utilized by chemists worldwide to improve the enantioselectivity for various catalytic reactions, such as conjugative addition, Tsuji-Trost reaction, C–H activation, cyclopropanation, etc. | 4 | Stereochemistry |
Some organic materials pass through intermediate states between solid and liquid; these states are called mesophases. Attention has been directed to mesophases because they enable display devices and have become commercially important through the so-called liquid-crystal technology. Phase diagrams are used to describe the occurrence of mesophases. | 7 | Physical Chemistry |
The AAG Gold Medal is the highest award given by the international Association of Applied Geochemists (AAG). It recognizes recipients' lifetime achievements, or significant contributions to geochemistry and its applications. The medal is minted with the name of the recipient and the year of the award from two troy ounces of silver bullion. | 9 | Geochemistry |
Experimentally, the concentration of the molecule complex [AB] is obtained indirectly from the measurement of the concentration of a free molecules, either [A] or [B].
In principle, the total amounts of molecule [A] and [B] added to the reaction are known.
They separate into free and bound components according to the mass conservation principle:
To track the concentration of the complex [AB], one substitutes the concentration of the free molecules ([A] or [B]), of the respective conservation equations, by the definition of the dissociation constant,
This yields the concentration of the complex related to the concentration of either one of the free molecules | 7 | Physical Chemistry |
Since 2000, light scattering systems have been used for biomedical applications such as the study of cellular morphology as well as the diagnosis of dysplasia. Variations in scattering distributions as a function of angle or wavelength have been used to deduce information regarding the size of cells and subcellular objects such as nuclei and organelles. These size measurements can then be used diagnostically to detect tissue changes—including neoplastic changes (those leading to cancer).
Light scattering spectroscopy has been used to detect dysplasia in the colon, bladder, cervix, and esophagus of human patients. Light scattering has also been used to detect Barrett's esophagus, a metaplastic condition with a high probability of leading to dysplasia.
However, in contrast with a/LCI, these techniques all rely on total intensity based measurements, which lack the ability to provide results as a function of depth in the tissue. | 7 | Physical Chemistry |
When we stretch a piece of rubber, e.g. a rubber band, we notice that it deforms uniformly, lengthwise. Every element along its length experiences the same extension factor as the entire sample. If we release one end, the sample snaps back to its original length very rapidly, too fast for our eye to resolve the process. Our intuitive expectation is that it returns to its original length in the same manner as when it was stretched, i. e. uniformly. However, this is not what happens. Experimental observations by Mrowca et al. show a surprising behavior. To capture the extremely fast retraction dynamics, they utilized a clever experimental method devised by Exner and Stefan in 1874, well before high-speed electronic measuring devices were invented. Their method consisted of a rapidly rotating glass cylinder which, after being coated with lamp black, was placed next to the stretched rubber sample. Styli, attached to the mid-point and free end of the rubber sample, were held in contact with the glass cylinder. Then, as the free end of the rubber snapped back, the styli traced out helical paths in the lamp black coating of the rotating cylinder. By adjusting the rotation speed of the cylinder, they could record the position of the styli in less than one complete rotation. The trajectories were transferred to a graph by rolling the cylinder on a piece of damp blotter paper. The mark left by a stylus appeared as a white line (no lamp black) on the paper.
Their data, plotted as the graph in Fig. 5, shows the position of end and midpoint styli as the sample rapidly retracts to its original length. The sample was initially stretched 9.5” beyond its unstrained length and then released. The styli returned to their original positions (displacement of 0”) in a little over 6 ms. The linear behavior of the displacement vs. time indicates that, after a brief acceleration, both the end and the midpoint of the sample snapped back at a constant velocity of about 50 m/s or 112 mph. However, the midpoint stylus did not start to move until about 3 ms after the end was released. Evidently, the retraction process travels as a wave, starting at the free end.
At high extensions some of the energy stored in the stretched network chain is due to a change in its entropy, but most of the energy is stored in bond distortions (regime II, above) which do not involve an entropy change. If one assumes that all of the stored energy is converted to kinetic energy, the retraction velocity may be calculated directly from the familiar conservation equation E = mv. Numerical simulations, based on the Molecular Kink paradigm, predict velocities consistent with this experiment. | 7 | Physical Chemistry |
The advantages are:
*Decrease in yield strength, therefore it is easier to work and uses less energy or force
*Increase in ductility
*Elevated temperatures increase diffusion which can remove or reduce chemical inhomogeneities
*Pores may reduce in size or close completely during deformation
*In steel, the weak, ductile, face-centered-cubic austenite microstructure is deformed instead of the strong body-centered-cubic ferrite microstructure found at lower temperatures
Usually the initial workpiece that is hot worked was originally cast. The microstructure of cast items does not optimize the engineering properties, from a microstructure standpoint. Hot working improves the engineering properties of the workpiece because it replaces the microstructure with one that has fine spherical shaped grains. These grains increase the strength, ductility, and toughness of the material.
The engineering properties can also be improved by reorienting the inclusions (impurities). In the cast state the inclusions are randomly oriented, which, when intersecting the surface, can be a propagation point for cracks. When the material is hot worked the inclusions tend to flow with the contour of the surface, creating stringers. As a whole the strings create a flow structure, where the properties are anisotropic (different based on direction). With the stringers oriented parallel to the surface it strengthens the workpiece, especially with respect to fracturing. The stringers act as "crack-arrestors" because the crack will want to propagate through the stringer and not along it.
The disadvantages are:
*Undesirable reactions between the metal and the surrounding atmosphere (scaling or rapid oxidation of the workpiece)
*Less precise tolerances due to thermal contraction and warping from uneven cooling
*Grain structure may vary throughout the metal for various reasons
*Requires a heating unit of some kind such as a gas or diesel furnace or an induction heater, which can be very expensive | 8 | Metallurgy |
In dilatational interfacial rheology, the size of the interface is changing over time. The change in the surface stress or surface tension of the interface is being measured during this deformation. Based on the response, interfacial viscoelasticity is calculated according to well established theories:
where
* |E| is the complex surface dilatational modulus
* γ is the surface tension or interfacial tension of the interface
* A is the interfacial area
* δ is the phase angle difference between the surface tension and area
* E’<nowiki/>' is the elastic (storage) modulus
* E’ is the viscous (loss) modulus
Most commonly, the measurement of dilational interfacial rheology is conducted with an optical tensiometer combined to a pulsating drop module. A pendant droplet with surface active molecules in it is formed and pulsated sinusoidally. The changes in the interfacial area causes changes in the molecular interactions which then changes the surface tension. Typical measurements include performing a frequency sweep for the solution to study the kinetics of the surfactant.
In another measurement method suitable especially for insoluble surfactants, a Langmuir trough is used in an oscillating barrier mode. In this case, two barriers that limit the interfacial area are being oscillated sinusoidally and the change in surface tension measured. | 7 | Physical Chemistry |
In metal borides, the bonding of boron varies depending on the atomic ratio B/M. Diborides have B/M = 2, as in the well-known superconductor MgB; they crystallize in a hexagonal AlB-type layered structure. Hexaborides have B/M = 6 and form a three-dimensional boron framework based on a boron octahedron (Fig. 1a). Tetraborides, i.e. B/M = 4, are mixtures of diboride and hexaboride structures. Cuboctahedron (Fig. 1b) is the structural unit of dodecaborides, which have a cubic lattice and B/M = 12. When the composition ratio exceeds 12, boron forms B icosahedra (Fig. 1c) which are linked into a three-dimensional boron framework, and the metal atoms reside in the voids of this framework.
This complex bonding behavior originates from the fact that boron has only three valence electrons; this hinders tetrahedral bonding as in diamond or hexagonal bonding as in graphite. Instead, boron atoms form polyhedra. For example, three boron atoms make up a triangle where they share two electrons to complete the so-called three-center bonding. Boron polyhedra, such as B octahedron, B cuboctahedron and B icosahedron, lack two valence electrons per polyhedron to complete the polyhedron-based framework structure. Metal atoms need to donate two electrons per boron polyhedron to form boron-rich metal borides. Thus, boron compounds are often regarded as electron-deficient solids. The covalent bonding nature of metal boride compounds also give them their hardness and inert chemical reactivity property.
Icosahedral B compounds include α-rhombohedral boron (BC), β-rhombohedral boron (MeB, 23≤x), α-tetragonal boron (BBC), β-tetragonal boron (β-AlB), AlB or AlCB, YB, YB, YB, NaB or MgAlB, γ-AlB, BeB and SiB.
YB and YB decompose without melting that hinders their growth as single crystals by the floating zone method. However, addition of a small amount of Si solves this problem and results in single crystals with the stoichiometry of YBSi. This stabilization technique allowed the synthesis of some other boron-rich rare-earth borides.
Albert and Hillebrecht reviewed binary and selected ternary boron compounds containing main-group elements, namely, borides of the alkali and alkaline-earth metals, aluminum borides and compounds of boron and the nonmetals C, Si, Ge, N, P, As, O, S and Se. They, however, excluded the described here icosahedron-based rare-earth borides. Note that rare-earth elements have d- and f-electrons that complicates chemical and physical properties of their borides. Werheit et al. reviewed Raman spectra of numerous icosahedron-based boron compounds.
Figure 2 shows a relationship between the ionic radius of trivalent rare-earth ions and the composition of some rare-earth borides. Note that scandium has many unique boron compounds, as shown in figure 2, because of the much smaller ionic radius compared with other rare-earth elements.
In understanding the crystal structures of rare-earth borides, it is important to keep in mind the concept of partial site occupancy, that is, some atoms in the described below unit cells can take several possible positions with a given statistical probability. Thus, with the given statistical probability, some of the partial-occupancy sites in such a unit cell are empty, and the remained sites are occupied. | 3 | Analytical Chemistry |
Etching is the immersion of the part into the chemical bath, and the action of the chemical on the part to be milled. The time spent immersed in the chemical bath determines the depth of the resulting etch; this time is calculated via the formula:
where E is the rate of etching (usually abbreviated to etch rate), s is the depth of the cut required, and t is the total immersion time. Etch rate varies based on factors such as the concentration and composition of the etchant, the material to be etched, and temperature conditions. Due to its inconstant nature, etch rate is often determined experimentally immediately prior to the etching process. A small sample of the material to be cut, of the same material specification, heat-treatment condition, and approximately the same thickness is etched for a certain time; after this time, the depth of the etch is measured and used with the time to calculate the etch rate. Aluminium is commonly etched at rates around , and magnesium about | 8 | Metallurgy |
Tom filed at least five patents in the UK and two in the US. He invented and patented the technology used at Thornaby as the Whitwell Heating Stove. Over two hundred stoves were installed in over 70 furnaces around the globe. He also patented a continuous brick-burning kiln and a more efficient fire grate. | 8 | Metallurgy |
Alarm photosynthesis represents an unknown photosynthetic variation to be added to the already known C4 and CAM pathways. However, alarm photosynthesis, in contrast to these pathways, operates as a biochemical pump that collects carbon from the organ interior (or from the soil) and not from the atmosphere. | 5 | Photochemistry |
The significance of peptide plane flips in the dynamics of the native state has been inferred in some proteins by comparing crystal structures of the same protein in multiple conformations. For example, peptide flips have been described as significant in the catalytic cycle of flavodoxin and in the formation of amyloid structures, where their ability to provide a low-energy pathway between beta sheet and the so-called alpha sheet conformation is suggested to facilitate the early stages of amyloidogenesis. Peptide plane flipping may also be significant in the early stages of protein folding. | 1 | Biochemistry |
Liebig formulated his own theory claiming that the production of alcohol was not a biological process but a chemical process, discrediting the idea that fermentation could occur due to microscopic organisms. He believed that vibrations emanating from the decomposition of organic matter would spread to the sugar resulting in the production of solely carbon dioxide and alcohol.
The change was facilitated by ferment or yeast, which has the characters of a compound of nitrogen in the state of putrefaction. Given that the ferment's susceptibility to change, it is submitted to decomposition, by the action of air (from which oxygen is provided), water (from which moisture is obtained), and a favorable temperature. Prior to contact with oxygen, the constituents are arranged together without action on each other. Through the oxygen, the state of rest (or equilibrium) of the attractions that keep the elements together has been disturbed. As a consequence of this disturbance, a separation or new arrangement of the elements has been formed. Fermentation occurs due to the transference of molecular instability from the ferment (atoms in motion) to the sugar molecules, and continues as long as the decomposition of the ferment continues.
Liebig's view of fermentation can be said to fall under a mechanism point of view. From his work, he saw that fermentation, as well as other catalysts happened by a chemical and mechanical process. | 1 | Biochemistry |
Amorphous materials have an internal structure consisting of interconnected structural blocks that can be similar to the basic structural units found in the corresponding crystalline phase of the same compound. Unlike in crystalline materials, however, no long-range order exists. Amorphous materials therefore cannot be defined by a finite unit cell. Statistical methods, such as the atomic density function and radial distribution function, are more useful in describing the structure of amorphous solids.
Although amorphous materials lack long range order, they exhibit localized order on small length scales. Localized order in amorphous materials can be categorized as short or medium range order. By convention, short range order extends only to the nearest neighbor shell, typically only 1-2 atomic spacings. Medium range order is then defined as the structural organization extending beyond the short range order, usually by 1-2 nm. | 7 | Physical Chemistry |
The Albion process is an atmospheric leaching process for processing zinc concentrate, refractory copper and refractory gold. The process is important because it is the most cost-effective method currently in use for extracting both the zinc and lead from concentrates that contain high lead levels (7% or greater). Zinc and lead often occur together and large remaining zinc deposits contain levels of lead that exceed what can be economically extracted through other techniques. The Albion process is not sensitive to the concentration grade and gives favorable recovery with both low grade and dirty concentrates. Environmental impact is also claimed to be mitigated using this technology because in contrast to other methods, sulfur dioxide is not emitted and less energy is consumed over all. | 8 | Metallurgy |
The term kodecyte is used to describe cells with detectable Function-Spacer-Lipid (FSL) constructs, and in concert, the term kodevirion (pronounced co-da-virion), is used to describe virions with detectable FSL constructs.
The method for labeling virions with FSL constructs is simple, non covalent and only involves incubation of the virion with the FSL construct in saline for a few hours – nothing further is required. The FSL construct will spontaneously, stably and quantitatively incorporate into the virion membrane. Virions have been labelled with fluorescent (FSL-FLRO4) and radioactive iodine (FSL-125I). FSL-FLRO4 could be shown to label virions in a dose dependent manner and could be visualized by flow cytometry either directly, or indirectly if the virion had bound to the cell or fused with the cell membrane. FSLs do not appear to significantly affect the virions infectivity or their ability to bind target cells, probably because they integrate into the membrane without exposing the virion to chemical agents or covalent modification. | 1 | Biochemistry |
There are a few common methods for filling the mold cavity: gravity, low-pressure, high-pressure, and vacuum.
Vacuum filling, also known as counter-gravity filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring. There is also less turbulence, so the gating system can be simplified since it does not have to control turbulence. Plus, because the metal is drawn from below the top of the pool the metal is free from dross and slag, as these are lower density (lighter) and float to the top of the pool. The pressure differential helps the metal flow into every intricacy of the mold. Finally, lower temperatures can be used, which improves the grain structure. The first patented vacuum casting machine and process dates to 1879.
Low-pressure filling uses 5 to 15 psig (35 to 100 kPag) of air pressure to force liquid metal up a feed tube into the mold cavity. This eliminates turbulence found in gravity casting and increases density, repeatability, tolerances, and grain uniformity. After the casting has solidified the pressure is released and any remaining liquid returns to the crucible, which increases yield. | 8 | Metallurgy |
Deamination of adenine results in the formation of hypoxanthine. Hypoxanthine, in a manner analogous to the imine tautomer of adenine, selectively base pairs with cytosine instead of thymine. This results in a post-replicative transition mutation, where the original A-T base pair transforms into a G-C base pair. | 1 | Biochemistry |
The pH of an alkaline soil can be reduced by adding acidifying agents or acidic organic materials. Elemental sulfur (90–99% S) has been used at application rates of – it slowly oxidizes in soil to form sulfuric acid. Acidifying fertilizers, such as ammonium sulfate, ammonium nitrate and urea, can help to reduce the pH of a soil because ammonium oxidises to form nitric acid. Acidifying organic materials include peat or sphagnum peat moss.
However, in high-pH soils with a high calcium carbonate content (more than 2%), it can be very costly and/or ineffective to attempt to reduce the pH with acids. In such cases, it is often more efficient to add phosphorus, iron, manganese, copper and/or zinc instead, because deficiencies of these nutrients are the most common reasons for poor plant growth in calcareous soils. | 9 | Geochemistry |
The major complication of IVF is the risk of multiple births. This is directly related to the practice of transferring multiple embryos at embryo transfer. Multiple births are related to increased risk of pregnancy loss, obstetrical complications, prematurity, and neonatal morbidity with the potential for long term damage. Strict limits on the number of embryos that may be transferred have been enacted in some countries (e.g. Britain, Belgium) to reduce the risk of high-order multiples (triplets or more), but are not universally followed or accepted. Spontaneous splitting of embryos in the uterus after transfer can occur, but this is rare and would lead to identical twins. A double blind, randomised study followed IVF pregnancies that resulted in 73 infants, and reported that 8.7% of singleton infants and 54.2% of twins had a birth weight of less than . There is some evidence that making a double embryo transfer during one cycle achieves a higher live birth rate than a single embryo transfer; but making two single embryo transfers in two cycles has the same live birth rate and would avoid multiple pregnancies. | 1 | Biochemistry |
The nanoDSF technology was used to confirm on-target binding of BI-3231 to HSD17B13 and to elucidate its uncompetitive mode of inhibition with regards to NAD. | 1 | Biochemistry |
Magma oceans are vast fields of surface magma that exist during periods of a planets or some natural satellites accretion when the celestial body is completely or partly molten.
In the early Solar System, magma oceans were formed by the melting of planetesimals and planetary impacts. Small planetesimals are melted by the heat provided by the radioactive decay of aluminium-26. As planets grew larger, the energy was then supplied from giant impacts with other planetary bodies. Magma oceans are integral parts of planetary formation as they facilitate the formation of a core through metal segregation and an atmosphere and hydrosphere through degassing. Evidence exists to support the existence of magma oceans on both the Earth and the Moon. Magma oceans may survive for millions to tens of millions of years, interspersed by relatively mild conditions. | 9 | Geochemistry |
DNA molecules were fixed on molten agarose developed between a cover slip and a microscope slide. Restriction enzyme was pre-mixed with the molten agarose before DNA placement and cleavage was triggered by addition of magnesium. | 1 | Biochemistry |
Several isozymes of malate dehydrogenase exist. There are two main isoforms in eukaryotic cells. One is found in the mitochondrial matrix, participating as a key enzyme in the citric acid cycle that catalyzes the oxidation of malate. The other is found in the cytoplasm, assisting the malate-aspartate shuttle with exchanging reducing equivalents so that malate can pass through the mitochondrial membrane to be transformed into oxaloacetate for further cellular processes.
Humans and most other mammals express the following two malate dehydrogenases: | 1 | Biochemistry |
Pauling's rules are five rules published by Linus Pauling in 1929 for predicting and rationalizing the crystal structures of ionic compounds. | 4 | Stereochemistry |
Fas forms the death-inducing signaling complex (DISC) upon ligand binding. Membrane-anchored Fas ligand trimer on the surface of an adjacent cell causes oligomerization of Fas.
Recent studies which suggested the trimerization of Fas could not be validated. Other models suggested the oligomerization up to 5–7 Fas molecules in the DISC.
This event is also mimicked by binding of an agonistic Fas antibody, though some evidence suggests that the apoptotic signal induced by the antibody is unreliable in the study of Fas signaling. To this end, several clever ways of trimerizing the antibody for in vitro research have been employed.
Upon ensuing death domain (DD) aggregation, the receptor complex is internalized via the cellular endosomal machinery. This allows the adaptor molecule FADD to bind the death domain of Fas through its own death domain.
FADD also contains a death effector domain (DED) near its amino terminus, which facilitates binding to the DED of FADD-like interleukin-1 beta-converting enzyme (FLICE), more commonly referred to as caspase-8. FLICE can then self-activate through proteolytic cleavage into p10 and p18 subunits, two each of which form the active heterotetramer enzyme. Active caspase-8 is then released from the DISC into the cytosol, where it cleaves other effector caspases, eventually leading to DNA degradation, membrane blebbing, and other hallmarks of apoptosis.
Recently, Fas has also been shown to promote tumor growth, since during tumor progression, it is frequently downregulated or cells are rendered apoptosis resistant. Cancer cells in general, regardless of their Fas apoptosis sensitivity, depend on constitutive activity of Fas. This is stimulated by cancer-produced Fas ligand for optimal growth.
Although Fas has been shown to promote tumor growth in the above mouse models, analysis of the human cancer genomics database revealed that FAS is not significantly focally amplified across a dataset of 3131 tumors (FAS is not an oncogene), but is significantly focally deleted across the entire dataset of these 3131 tumors, suggesting that FAS functions as a tumor suppressor in humans.
In cultured cells, FasL induces various types of cancer cell apoptosis through the Fas receptor. In AOM-DSS-induced colon carcinoma and MCA-induced sarcoma mouse models, it has been shown that Fas acts as a tumor suppressor. Furthermore, the Fas receptor also mediates tumor-specific cytotoxic T lymphocyte (CTL) anti-tumor cytotoxicity. In addition to the well-described on-target CTL anti-tumor cytotoxicity, Fas has been ascribed with a distinct function – the induction of bystander tumor cell death even amongst cognate antigen non-expressing (bystander) cells. CTL-mediated bystander killing was described by the Fleischer Lab in 1986 and later attributed to fas-mediated lysis in vitro by the Austin Research Institute, Cellular Cytotoxicity Laboratory. More recently, fas-mediated bystander tumor cell killing was demonstrated in vivo by the Lymphoma Immunotherapy Program at Mount Sinai School of Medicine using T cells and CAR-T cells, similar to additional in vitro work using bispecific antibodies performed at Amgen. | 1 | Biochemistry |
Spinor condensates are degenerate Bose gases that have degrees of freedom arising from the internal spin of the constituent particles
They are described by a multi-component (spinor) order parameter.
Since their initial experimental realisation,
a wealth of studies have appeared, both
experimental and theoretical, focusing
on the physical properties of spinor condensates, including their
ground states, non-equilibrium dynamics, and
vortices. | 7 | Physical Chemistry |
Methylene (IUPAC name: Methylidene, also called carbene or methene) is an organic compound with the chemical formula (also written ). It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct.
Methylene is the simplest carbene. It is usually detected only at very low temperatures, or as a short-lived intermediate in chemical reactions. | 0 | Organic Chemistry |
Initially IOP attempted to sell the company as a complete unit but when this was unsuccessful they decided to sell the Fulmer companies at Stoke Poges and Slough, and the Yarsley operation at Redhill as separate entities.
In 1989 exploratory talks with an American testing and consultancy company were held regarding a merger with Yarsley but no agreement could be reached. An approach was then made to the UK subsidiary of the Swiss company Societe Generale de Surveillance S.A. (SGS), who were particularly interested in strengthening their activities in quality assurance consultancy and certification. Agreement was soon reached for them to purchase Yarsley, and the sale took place on November 30, 1990. The Fulmer activities at Stoke Poges were merged with
BNF Metals Technology Centre at Wantage Oxfordshire, and the manufacturing unit at Slough was acquired by Sintek of Germany. | 8 | Metallurgy |
A pressure–volume diagram (or PV diagram, or volume–pressure loop) is used to describe corresponding changes in volume and pressure in a system. They are commonly used in thermodynamics, cardiovascular physiology, and respiratory physiology.
PV diagrams, originally called indicator diagrams, were developed in the 18th century as tools for understanding the efficiency of steam engines. | 7 | Physical Chemistry |
There are slight iron isotopic variations in the oceans relative to IRMM-014, which likely reflect variations in the biogeochemical cycling of iron within a given ocean basin. In the southeastern Atlantic, δFe values between -0.13 and +0.21‰ have been measured. In the north Atlantic, δFe values between -1.35 and +0.80‰ have been measured. In the equatorial Pacific δFe values between -0.03 and +0.58‰ have been measured. The supply of aerosol iron particles to the ocean have an isotopic composition of approximately 0‰. Dissolved iron riverine input to the ocean is isotopically light relative to igneous rocks, with δFe values between -1 and 0‰.
Most modern marine sediments have δFe values similar to those of igneous δFe values. Marine ferromanganese nodules have δFe values between -0.8 and 0‰. | 9 | Geochemistry |
Degradation depends on the sensitivity of the material to the wavelength of X-rays used, the total dose of the X-rays, the temperature of the surface and the level of the vacuum. Metals, alloys, ceramics and most glasses are not measurably degraded by either non-monochromatic or monochromatic X-rays. Some, but not all, polymers, catalysts, certain highly oxygenated compounds, various inorganic compounds and fine organics are. Non-monochromatic X-ray sources produce a significant amount of high energy Bremsstrahlung X-rays (1–15 keV of energy) which directly degrade the surface chemistry of various materials. Non-monochromatic X-ray sources also produce a significant amount of heat (100 to 200 °C) on the surface of the sample because the anode that produces the X-rays is typically only 1 to away from the sample. This level of heat, when combined with the Bremsstrahlung X-rays, acts to increase the amount and rate of degradation for certain materials. Monochromatised X-ray sources, because they are farther away (50–100 cm) from the sample, do not produce noticeable heat effects. In those, a quartz monochromator system diffracts the Bremsstrahlung X-rays out of the X-ray beam, which means the sample is only exposed to one narrow band of X-ray energy. For example, if aluminum K-alpha X-rays are used, the intrinsic energy band has a FWHM of 0.43 eV, centered on 1,486.7 eV (E/ΔE = 3,457). If magnesium K-alpha X-rays are used, the intrinsic energy band has a FWHM of 0.36 eV, centered on 1,253.7 eV (E/ΔE = 3,483). These are the intrinsic X-ray line widths; the range of energies to which the sample is exposed depends on the quality and optimization of the X-ray monochromator. Because the vacuum removes various gases (e.g., O, CO) and liquids (e.g., water, alcohol, solvents, etc.) that were initially trapped within or on the surface of the sample, the chemistry and morphology of the surface will continue to change until the surface achieves a steady state. This type of degradation is sometimes difficult to detect. | 7 | Physical Chemistry |
The earliest smelted iron object from Europe is a knife blade from the Catacomb culture in present day Ukraine, dated to c. 2500 BC. During most of the Middle and Late Bronze Age in Europe, iron was present, though scarce. It was used for personal ornaments and small knives, for repairs on bronzes, and for bimetallic items. Early smelted iron finds from central Europe include an iron knife or sickle from Ganovce in Slovakia, possibly dating from the 18th century BC, an iron ring from Vorwohlde in Germany dating from circa the 15th century BC, and an iron chisel from Heegermühle in Germany dating from circa 1000 BC.
Iron metallurgy began to be practised in Scandinavia during the later Bronze Age from at least the 9th century BC. In the 11th century BC iron swords replaced bronze swords in Southern Europe, especially in Greece, and in the 10th century BC iron became the prevailing metal in use. In the Carpathian Basin there is a significant increase in iron finds dating from the 10th century BC onwards, with some finds possibly dating as early as the 12th century BC. Iron swords have been found in central Europe dating from the 10th century BC, however the Iron Age began in earnest with the Hallstatt culture from 800 BC.
From 500 BC the La Tène culture saw a significant increase in iron production, with iron metallurgy also becoming common in southern Scandinavia. North of Sweden saw steel manufacturing dating back to around 0 AD through the eastern-western migration of hunter-gatherers in the Cap of the North. The spread of ironworking in Central and Western Europe is associated with Celtic expansion. Celtic smiths produced steel from circa 800 BC as part of the production of swords, and the production of high-carbon steel is attested in Britain after circa 490 BC. By the 1st century BC, Noric steel was famous for its quality and sought-after by the Roman military.
The annual iron output of the Roman Empire is estimated at 84,750 t. | 8 | Metallurgy |
The Wigner–Seitz cell always has the same point symmetry as the underlying Bravais lattice. For example, the cube, truncated octahedron, and rhombic dodecahedron have point symmetry O, since the respective Bravais lattices used to generate them all belong to the cubic lattice system, which has O point symmetry. | 3 | Analytical Chemistry |
The synthesis of molograms on the sensor chip is realized with properly designed surface chemistry and reactive immersion lithography (RIL). Through the RIL process the biomolecular recognition structure of the mologram on a light-sensitive non-fouling graft copolymer layer can be created by standard lithography techniques. The copolymer layer is functionalized with photocleavable protection groups that upon illumination create reactive amines. Subsequent surface chemistry steps enable an easy tailoring of recognition molecules specific to the desired analytical application. | 1 | Biochemistry |
Phenol–chloroform extraction is a liquid-liquid extraction technique in molecular biology used to separate nucleic acids from proteins and lipids. | 1 | Biochemistry |
In contact with water, hydrogen is created. Hence, sodium–potassium alloys are used as desiccants in drying solvents prior to distillation. | 8 | Metallurgy |
Sertraline and amitriptyline inhibit butyrylcholinesterase and cause prolonged paralysis. Mivacurium causes prolonged paralysis for patients chronically taking sertraline. | 1 | Biochemistry |
A definition of thermodynamic entropy can be based entirely on certain properties of the relation of adiabatic accessibility that are taken as axioms in the Lieb-Yngvason approach. In the following list of properties of the operator, a system is represented by a capital letter, e.g. X, Y or Z. A system X whose extensive parameters are multiplied by is written . (e.g. for a simple gas, this would mean twice the amount of gas in twice the volume, at the same pressure.) A system consisting of two subsystems X and Y is written (X,Y). If and are both true, then each system can access the other and the transformation taking one into the other is reversible. This is an equivalence relationship written . Otherwise, it is irreversible. Adiabatic accessibility has the following properties:
*Reflexivity:
*Transitivity: If and then
*Consistency: if and then
*Scaling Invariance: if and then
*Splitting and Recombination: for all
*Stability: if then
The entropy has the property that if and only if and if and only if in accord with the Second Law. If we choose two states and such that and assign entropies 0 and 1 respectively to them, then the entropy of a state X where is defined as: | 7 | Physical Chemistry |
mTORC1 activation is required for myofibrillar muscle protein synthesis and skeletal muscle hypertrophy in humans in response to both physical exercise and ingestion of certain amino acids or amino acid derivatives. Persistent inactivation of mTORC1 signaling in skeletal muscle facilitates the loss of muscle mass and strength during muscle wasting in old age, cancer cachexia, and muscle atrophy from physical inactivity. mTORC2 activation appears to mediate neurite outgrowth in differentiated mouse neuro2a cells. Intermittent mTOR activation in prefrontal neurons by β-hydroxy β-methylbutyrate inhibits age-related cognitive decline associated with dendritic pruning in animals, which is a phenomenon also observed in humans. | 1 | Biochemistry |
Hydrocarbon mixtures are a group of various volatile, highly flammable, mixtures used chiefly as nonpolar solvents. | 0 | Organic Chemistry |
During the M-to-G1 transition, pRb is then progressively dephosphorylated by PP1, returning to its growth-suppressive hypophosphorylated state.
pRb family proteins are components of the DREAM complex composed of DP, E2F4/5, RB-like (p130/p107) And MuvB (Lin9:Lin37:Lin52:RbAbP4:Lin54). The DREAM complex is assembled in Go/G1 and maintains quiescence by assembling at the promoters of > 800 cell-cycle genes and mediating transcriptional repression. Assembly of DREAM requires DYRK1A (Ser/Thr kinase) dependant phosphorylation of the MuvB core component, Lin52 at Serine28. This mechanism is crucial for recruitment of p130/p107 to the MuvB core and thus DREAM assembly. | 1 | Biochemistry |
The Ellingham curve for aluminium lies below the curves of most metals such as chromium, iron, etc. This fact indicates that aluminium can be used as the reducing agent for oxides of all these metals. This result is illustrated as follows:
The free energies of formation of chromium(III) oxide and aluminium oxide per mole of oxygen consumed are -541 kJ and -827 kJ respectively. The processes are:
The second equation minus the first equation gives:
So aluminium oxide is more stable than chromium oxide (at least at normal temperatures, and in fact all the way up to the decomposition temperatures of the oxides). Since the Gibbs free energy change is negative, aluminium can reduce chromium oxide.
In pyrometallurgy, aluminium is used as a reducing agent in the alumino-thermic process or thermite process to extract chromium and manganese by reduction of their oxides. | 8 | Metallurgy |
There are a very large number of petrochemicals produced from the BTX aromatics. The following diagram shows the chains leading from the BTX components to some of the petrochemicals that can be produced from those components: | 7 | Physical Chemistry |
The orientation of a glide plane is given by the position of the symbol in the Hermann–Mauguin designation, just as with mirror planes.
They are noted by a, b, or c depending on which axis (direction) the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, which is along a quarter of either a face or space diagonal of the unit cell. The d glide is often called the diamond glide plane as it features in the diamond structure. In cases where there are two possibilities among a, b, and c (such as a or b), the letter e is used. (In these cases, centering entails that both glides occur.) To summarize:
* a, b, or c glide translation along half the lattice vector of this face.
* n glide translation along half a face diagonal.
* d glide planes with translation along a quarter of a face diagonal or of a space diagonal.
* e two glides with the same glide plane and translation along two (different) half-lattice vectors. | 3 | Analytical Chemistry |
The oldest and most commonly used atomizers in AAS are flames, principally the air-acetylene flame with a temperature of about 2300 °C and the nitrous oxide system (NO)-acetylene flame with a temperature of about 2700 °C. The latter flame, in addition, offers a more reducing environment, being ideally suited for analytes with high affinity to oxygen.
Liquid or dissolved samples are typically used with flame atomizers. The sample solution is aspirated by a pneumatic analytical nebulizer, transformed into an aerosol, which is introduced into a spray chamber, where it is mixed with the flame gases and conditioned in a way that only the finest aerosol droplets (< 10 μm) enter the flame. This conditioning process reduces interference, but only about 5% of the aerosolized solution reaches the flame because of it.
On top of the spray chamber is a burner head that produces a flame that is laterally long (usually 5–10 cm) and only a few mm deep. The radiation beam passes through this flame at its longest axis, and the flame gas flow-rates may be adjusted to produce the highest concentration of free atoms. The burner height may also be adjusted, so that the radiation beam passes through the zone of highest atom cloud density in the flame, resulting in the highest sensitivity.
The processes in a flame include the stages of desolvation (drying) in which the solvent is evaporated and the dry sample nano-particles remain, vaporization (transfer to the gaseous phase) in which the solid particles are converted into gaseous molecule, atomization in which the molecules are dissociated into free atoms, and ionization where (depending on the ionization potential of the analyte atoms and the energy available in a particular flame) atoms may be in part converted to gaseous ions.
Each of these stages includes the risk of interference in case the degree of phase transfer is different for the analyte in the calibration standard and in the sample. Ionization is generally undesirable, as it reduces the number of atoms that are available for measurement, i.e., the sensitivity.
In flame AAS a steady-state signal is generated during the time period when the sample is aspirated. This technique is typically used for determinations in the mg L range, and may be extended down to a few μg L for some elements. | 3 | Analytical Chemistry |
Gold deposits are formed via a very wide variety of geological processes. Deposits are classified as primary, alluvial or placer deposits, or residual or laterite deposits. Often a deposit will contain a mixture of all three types of ore.
Plate tectonics is the underlying mechanism for generating gold deposits. The majority of primary gold deposits fall into two main categories: lode gold deposits or intrusion-related deposits.
Lode gold deposits, also referred to as orogenic gold are generally high-grade, thin, vein and fault hosted. They are primarily made up of quartz veins also known as lodes or reefs, which contain either native gold or gold sulfides and tellurides. Lode gold deposits are usually hosted in basalt or in sediments known as turbidite, although when in faults, they may occupy intrusive igneous rocks such as granite.
Lode-gold deposits are intimately associated with orogeny and other plate collision events within geologic history. It is thought that most lode gold deposits are sourced from metamorphic rocks by the dehydration of basalt during metamorphism. The gold is transported up faults by hydrothermal waters and deposited when the water cools too much to retain gold in solution.
Intrusive related gold (Lang & Baker, 2001) is generally hosted in granites, porphyry, or rarely dikes. Intrusive related gold usually also contains copper, and is often associated with tin and tungsten, and rarely molybdenum, antimony, and uranium. Intrusive-related gold deposits rely on gold existing in the fluids associated with the magma (White, 2001), and the inevitable discharge of these hydrothermal fluids into the wall-rocks (Lowenstern, 2001). Skarn deposits are another manifestation of intrusive-related deposits.
Placer deposits are sourced from pre-existing gold deposits and are secondary deposits. Placer deposits are formed by alluvial processes within rivers and streams, and on beaches. Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as bends in rivers and behind boulders. Often placer deposits are found within sedimentary rocks and can be billions of years old, for instance the Witwatersrand deposits in South Africa. Sedimentary placer deposits are known as leads or deep leads.
Placer deposits are often worked by fossicking, and panning for gold is a popular pastime.
Laterite gold deposits are formed from pre-existing gold deposits (including some placer deposits) during prolonged weathering of the bedrock. Gold is deposited within iron oxides in the weathered rock or regolith, and may be further enriched by reworking by erosion. Some laterite deposits are formed by wind erosion of the bedrock leaving a residuum of native gold metal at surface.
A bacterium, Cupriavidus metallidurans plays a vital role in the formation of gold nuggets, by precipitating metallic gold from a solution of gold (III) tetrachloride, a compound highly toxic to most other microorganisms.
Similarly, Delftia acidovorans can form gold nuggets. | 9 | Geochemistry |
Pourbaix diagrams are widely used to describe the behaviour of chemical species in the hydrosphere. In this context, reduction potential is often used instead of . The main advantage is to directly work with a logarithm scale.
is a dimensionless number and can easily be related to by the equation:
Where, is the thermal voltage, with , the gas constant (), , the absolute temperature in Kelvin (298.15 K = 25 °C = 77 °F), and , the Faraday constant (96 485 coulomb/mol of ). Lambda, λ = ln(10) ≈ 2.3026.
Moreover,
: , an expression with a similar form to that of pH.
values in environmental chemistry ranges from −12 to +25, since at low or high potentials water will be respectively reduced or oxidized. In environmental applications, the concentration of dissolved species is usually set to a value between 10 M and 10 M for the determination of the equilibrium lines. | 7 | Physical Chemistry |
Neisseria meningitidis has multiple type II restriction endonuclease systems that are employed in natural genetic transformation. Natural genetic transformation is a process by which a recipient bacterial cell can take up DNA from a neighboring donor bacterial cell and integrate this DNA into its genome by recombination. Although early work on restriction modification systems focused on the benefit to bacteria of protecting themselves against invading bacteriophage DNA or other foreign DNA, it is now known that these systems can also be used to restrict DNA introduced by natural transformation from other members of the same, or related species.
In the pathogenic bacterium Neisseria meningitidis (meningococci), competence for transformation is a highly evolved and complex process where multiple proteins at the bacterial surface, in the membranes and in the cytoplasm interact with the incoming transforming DNA. Restriction-modification systems are abundant in the genus Neisseria. N. meningitidis has multiple type II restriction endonuclease systems. The restriction modification systems in N. meningitidis vary in specificity between different clades. This specificity provides an efficient barrier against DNA exchange between clades. Luria, on page 99 of his autobiography, referred to such a restriction behavior as "an extreme instance of unfriendliness." Restriction-modification appears to be a major driver of sexual isolation and speciation in the meningococci. Caugant and Maiden suggested that restriction-modification systems in meningococci may act to allow genetic exchange among very close relatives while reducing (but not completely preventing) genetic exchange among meningococci belonging to different clonal complexes and related species.
RM systems can also act as selfish genetic elements, forcing their maintenance on the cell through postsegregational cell killing.
Some viruses have evolved ways of subverting the restriction modification system, usually by modifying their own DNA, by adding methyl or glycosyl groups to it, thus blocking the restriction enzymes. Other viruses, such as bacteriophages T3 and T7, encode proteins that inhibit the restriction enzymes.
To counteract these viruses, some bacteria have evolved restriction systems which only recognize and cleave modified DNA, but do not act upon the host's unmodified DNA. Some prokaryotes have developed multiple types of restriction modification systems.
R-M systems are more abundant in promiscuous species, wherein they establish preferential paths of genetic exchange within and between lineages with cognate R-M systems. Because the repertoire and/or specificity of R-M systems in bacterial lineages vary quickly, the preferential fluxes of genetic transfer within species are expected to constantly change, producing time-dependent networks of gene transfer. | 1 | Biochemistry |
* Fellow, King's College, Cambridge University (1969–1973, 2007– for Life)
* Professor at H.E.J. Research Institute of Chemistry at Karachi University
* Professor Emeritus at H.E.J. Research Institute of Chemistry at Karachi University (2012)
* Coordinator General of COMSTECH(1996–2012)
* Federal Minister of Science & Technology (2000–2002)
* Federal Minister of Education (2002)
* Federal Minister/Chairman, Higher Education Commission, Pakistan (resigned due to govt issues)(2002–2008)
* Advisor to the Prime Minister of Pakistan on Science and Technology(2002–2008) | 0 | Organic Chemistry |
After creating a series of traditionally chiral calixarenes (through the addition of a chiral substituent group on the top or bottom rim of the macrocycle,) the first inherently chiral calixarenes were synthesized in 1982, though the molecules were not yet described as such. The inherently chiral calixarenes featured an XXYZ or WXYZ substitution pattern, such that the planar representation of the molecule does not show any chirality, and if the macrocycle were to be broken open, this would produce an achiral linear molecule. The chirality in these calixarenes is instead derived from the curvature of the molecule in space. | 4 | Stereochemistry |
Helium-4 is a liquid at normal pressure near absolute zero, a consequence of its high zero-point energy (ZPE). The ZPE of protons in a dense state is also high, and a decline in the ordering energy (relative to the ZPE) is expected at high pressures. Arguments have been advanced by Neil Ashcroft and others that there is a melting point maximum in compressed hydrogen, but also that there might be a range of densities, at pressures around 400 GPa, where hydrogen would be a liquid metal, even at low temperatures.
Geng predicted that the ZPE of protons indeed lowers the melting temperature of hydrogen to a minimum of at pressures of .
Within this flat region there might be an elemental mesophase intermediate between the liquid and solid state, which could be metastably stabilized down to low temperature and enter a supersolid state. | 7 | Physical Chemistry |
In colloidal chemistry, flocculation is a process by which colloidal particles come out of suspension to sediment in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended, under the form of a stable dispersion (where the internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation) and are not truly dissolved in solution.
Coagulation and flocculation are important processes in water treatment with coagulation aimed to destabilize and aggregate particles through chemical interactions between the coagulant and colloids, and flocculation to sediment the destabilized particles by causing their aggregation into floc. | 8 | Metallurgy |
δO can be used with ice cores to determine the temperature from when the ice was formed.
Lisiecki and Raymo (2005) used measurements of δO in benthic foraminifera from 57 globally distributed deep sea sediment cores, taken as a proxy for the total global mass of glacial ice sheets, to reconstruct the climate for the past five million years.
The stacked record of the 57 cores was orbitally tuned to an orbitally driven ice model, the Milankovitch cycles of 41 ky (obliquity), 26 ky (precession) and 100 ky (eccentricity), which are all assumed to cause orbital forcing of global ice volume. Over the past million years, there have been a number of very strong glacial maxima and minima, spaced by roughly 100 ky.
As the observed isotope variations are similar in shape to the temperature variations recorded for the past 420 ky at Vostok Station, the figure shown on the right aligns the values of δO (right scale) with the reported temperature variations from the Vostok ice core (left scale), following Petit et al. (1999). | 9 | Geochemistry |
Titanium aluminide (chemical formula TiAl), commonly gamma titanium, is an intermetallic chemical compound. It is lightweight and resistant to oxidation and heat, but has low ductility. The density of γ-TiAl is about 4.0 g/cm. It finds use in several applications including aircraft, jet engines, sporting equipment and automobiles. The development of TiAl based alloys began circa 1970. The alloys have been used in these applications only since about 2000.
Titanium aluminide has three major intermetallic compounds: gamma titanium aluminide (gamma TiAl, γ-TiAl), alpha 2-TiAl and TiAl. Among the three, gamma TiAl has received the most interest and applications. | 8 | Metallurgy |
Heteroatoms aside from the transition metal are a defining feature of heteropolymetalates. Many different elements can serve as heteroatoms but most common are Phosphate|, Silicate|, and Arsenate|. | 7 | Physical Chemistry |
Andrew Bruce Holmes (born 5 September 1943) is an Australian and British senior research chemist and professor at the Bio21 Institute, Melbourne, Australia, and the past President of the Australian Academy of Science. His research interests lie in the synthesis of biologically-active natural products (spanning therapeutic materials to new biotechnological probes) and optoelectronic polymers (with applications to electroluminescent flexible displays and organic solar cells). | 0 | Organic Chemistry |
The pentose phosphate pathway gets its name because it involves several intermediates that are phosphorylated five-carbon sugars (pentoses). This pathway provides monomers for many metabolic pathways by transforming glucose into the four-carbon sugar erythrose and the five-carbon sugar ribose; these are important monomers in many metabolic pathways. Many of the reactants in this pathway are similar to those in glycolysis, and both occur in cytosol. The ribose-5-phosphate can be transported into the nucleic acid metabolism, producing the basis of DNA and RNA monomers, the nucleotides. In meristematic cells, large amounts of DNA must be produced during the S-phase of a short cell cycle; this pathway is an extremely important part of the metabolism of these cells. In these cells, the pentose phosphate pathway is active and shifted in favor of ribose production. | 1 | Biochemistry |
Another mechanism involving the structure of the 3′-UTR is called alternative polyadenylation (APA), which results in mRNA isoforms that differ only in their 3′-UTRs. This mechanism is especially useful for complex organisms as it provides a means of expressing the same protein but in varying amounts and locations. It is utilized by about half of human genes. APA can result from the presence of multiple polyadenylation sites or mutually exclusive terminal exons. Since it can affect the presence of protein and miRNA binding sites, APA can cause differential expression of mRNA transcripts by influencing their stability, export to the cytoplasm, and translation efficiency. | 1 | Biochemistry |
Membership of the European Molecular Biology Organization (EMBO) is an award granted by the European Molecular Biology Organization (EMBO) in recognition of "research excellence and the outstanding achievements made by a life scientist".
, 88 EMBO Members and Associate Members have been awarded Nobel Prizes in either Physiology or Medicine, Chemistry or Physics. See :Category:Members of the European Molecular Biology Organization for examples of EMBO members. | 1 | Biochemistry |
One method for preparing β-phenethylamine, set forth in J. C. Robinson and H. R. Snyders Organic Syntheses' (published 1955), involves the reduction of benzyl cyanide with hydrogen in liquid ammonia, in the presence of a Raney-Nickel catalyst, at a temperature of 130 °C and a pressure of 13.8 MPa. Alternative syntheses are outlined in the footnotes to this preparation.
A much more convenient method for the synthesis of β-phenethylamine is the reduction of ω-nitrostyrene by lithium aluminium hydride in ether, whose successful execution was first reported by R. F. Nystrom and W. G. Brown in 1948.
Phenethylamine can also be produced via the cathodic reduction of benzyl cyanide in a divided cell.
Assembling phenethylamine structures for synthesis of compounds such as epinephrine, amphetamines, tyrosine, and dopamine by adding the beta-aminoethyl side chain to the phenyl ring is possible. This can be done via Friedel-Crafts acylation with N-protected acyl chlorides when the arene is activated, or by Heck reaction of the phenyl with N-vinyloxazolone, followed by hydrogenation, or by cross-coupling with beta-amino organozinc reagents, or reacting a brominated arene with beta-aminoethyl organolithium reagents, or by Suzuki cross-coupling. | 1 | Biochemistry |
During plastic deformation the work performed is the integral of the stress and strain in the plastic deformation regime. Although the majority of this work is converted to heat, some fraction (~1–5%) is retained in the material as defects—particularly dislocations. The rearrangement or elimination of these dislocations will reduce the internal energy of the system and so there is a thermodynamic driving force for such processes. At moderate to high temperatures, particularly in materials with a high stacking fault energy such as aluminium and nickel, recovery occurs readily and free dislocations will readily rearrange themselves into subgrains surrounded by low-angle grain boundaries.
The driving force is the difference in energy between the deformed and recrystallized state ΔE which can be determined by the dislocation density or the subgrain size and boundary energy (Doherty, 2005):
where ρ is the dislocation density, G is the shear modulus, b is the Burgers vector of the dislocations, γ is the subgrain boundary energy and d is the subgrain size. | 8 | Metallurgy |
EPIC-seq has demonstrated remarkable potential in noninvasive cancer detection, notably in the diagnosis of lung cancer, the leading cause of cancer-related mortality. Using EPIC-seq, researchers have achieved high accuracy in distinguishing between NSCLC patients, DLBCL patients and healthy individuals. | 1 | Biochemistry |
Recent studies have shown that SK channels do not only regulate afterhyperpolarization, they also have an effect on synaptic plasticity. This is the activity-dependent adaptation of the strength of synaptic transmission. Synaptic plasticity is an important mechanism underlying learning and memory processes. Apamin is expected to influence these processes by inhibiting SK channels. It has been shown that apamin enhances learning and memory in rats and mice. This may provide a basis for the use of apamin as a treatment for memory disorders and cognitive dysfunction. However, due to the risk of toxic effects, the therapeutic window is very narrow.
SK channel blockers may have a therapeutic effect on Parkinson's disease. Dopamine, which is depleted in this disease, will be released from midbrain dopaminergic neurons when these SK channels are inhibited. SK channels have also been proposed as targets for the treatment of epilepsy, emotional disorders and schizophrenia. | 1 | Biochemistry |
Extraction thimbles are rod-shape filter paper often used in soxhlet extractors or atomized extractors. It is ideal for very sensitive detection, the performance depends on the thickness of inner diameter. Also, it is usually used in areas of food control and environmental monitoring. | 3 | Analytical Chemistry |
* Kyoto Encyclopedia of Genes and Genomes ([http://www.kegg.jp/ KEGG]): a bioinformatics database containing information on genes, proteins, reactions, and pathways. The ‘KEGG Organisms’ section, which is divided into eukaryotes and prokaryotes, encompasses many organisms for which gene and DNA information can be searched by typing in the enzyme of choice.
* BioCyc, EcoCyc, and MetaCyc: [http://biocyc.org/ BioCyc] Is a collection of 3,000 pathway/genome databases (as of Oct 2013), with each database dedicated to one organism. For example, [http://ecocyc.org/ EcoCyc] is a highly detailed bioinformatics database on the genome and metabolic reconstruction of Escherichia coli, including thorough descriptions of E. coli signaling pathways and regulatory network. The EcoCyc database can serve as a paradigm and model for any reconstruction. Additionally, [http://biocyc.org/metacyc/index.shtml MetaCyc], an encyclopedia of experimentally defined metabolic pathways and enzymes, contains 2,100 metabolic pathways and 11,400 metabolic reactions (Oct 2013).
* [http://enzyme.expasy.org/ ENZYME]: An enzyme nomenclature database (part of the ExPASy proteonomics server of the Swiss Institute of Bioinformatics). After searching for a particular enzyme on the database, this resource gives you the reaction that is catalyzed. ENZYME has direct links to other gene/enzyme/literature databases such as KEGG, BRENDA, and PUBMED.
* [http://www.brenda-enzymes.info/ BRENDA]: A comprehensive enzyme database that allows for an enzyme to be searched by name, EC number, or organism.
* [http://bigg.ucsd.edu/ BiGG]: A knowledge base of biochemically, genetically, and genomically structured genome-scale metabolic network reconstructions.
* [https://web.archive.org/web/20120304065541/http://www.bioinformatics.leeds.ac.uk/metatiger/ metaTIGER]: Is a collection of metabolic profiles and phylogenomic information on a taxonomically diverse range of eukaryotes which provides novel facilities for viewing and comparing the metabolic profiles between organisms. | 1 | Biochemistry |
3-Azidocoumarin is an organic compound that is used in the area of bioconjugation. It is a derivative of coumarin, a natural product and precursor for the widely used Coumadin. Azidocoumarin has emerged as a widely applicable labeling agent in diverse biological systems. In particular, it participates in the aptly named click reaction with alkynes. Bioconjugation involves the labeling of certain cellular components and is applicable to fields such a proteomics and functional genomics with a detachable, fluorescent tag. | 1 | Biochemistry |
The proposed mechanism of how this mRNA secondary structure and the trp leader peptide could regulate transcription of the trp biosynthetic enzymes includes the following.
*RNAP initiates transcription of the trp promoter.
*RNAP pauses at about nucleotide 90 at a secondary structure (?the first one shown above?).
*Ribosomes engage this nascent mRNA and initiate translation of the leader peptide.
**RNAP is then "released" from its pause and continues transcription.
*When RNAP reaches the region of the potential terminator, whether it continues or not is dependent on the position of the ribosome "trailing behind".
**If the ribosome stalls at the tandem Trp codons, waiting for the appropriate tRNA, region 1 is sequestered within the ribosome and thus cannot base pair with region 2. This means that region 2 and 3 become based paired before region 4 can be transcribed. This forces region 4 when it is made to be single stranded, preventing the formation of the region 3/4 terminator structure. Transcription will then continue.
**If the ribosome translates the leader peptide with no hesitation, it then covers a portion of region 2 preventing it from base pairing with region 3. Then when region 4 is transcribed, it forms a stem and loop with region 3 and transcription is terminated, generating a ca. 140 base transcript.
*This mechanism of control measures the amount of available, charged Trp-tRNA.
The location of ribosomes determines which alternate secondary structures form. | 1 | Biochemistry |
PAVA spray is an incapacitant spray similar to pepper spray. It is dispensed from a handheld canister, in a liquid stream. It contains a 0.3% solution of pelargonic acid vanillylamide (PAVA), also called nonivamide, a synthetic capsaicinoid (analogue of capsaicin), in a solvent of aqueous ethanol. The propellant is nitrogen. This solution has been selected because this is the minimum concentration which will fulfill the purpose of the equipment; namely to minimise a person's capacity for resistance, without unnecessarily prolonging their discomfort.
PAVA is significantly more potent than CS gas. The liquid stream is a spray pattern and has a maximum effective range of up to . Maximum accuracy, however, will be achieved over a distance of . The operating distance is the distance between the canister and the subject's eyes, not the distance between the user and the subject. | 1 | Biochemistry |
The technique of selecting only one embryo to transfer to the woman is called elective-single embryo transfer (e-SET) or, when embryos are at the blastocyst stage, it can also be called elective single blastocyst transfer (eSBT). It significantly lowers the risk of multiple pregnancies, compared with e.g. Double Embryo Transfer (DET) or double blastocyst transfer (2BT), with a twinning rate of approximately 3.5% in sET compared with approximately 38% in DET, or 2% in eSBT compared with approximately 25% in 2BT. At the same time, pregnancy rates is not significantly less with eSBT than with 2BT. That is, the cumulative live birth rate associated with single fresh embryo transfer followed by a single frozen and thawed embryo transfer is comparable with that after one cycle of double fresh embryo transfer. Furthermore, SET has better outcomes in terms of mean gestational age at delivery, mode of delivery, birthweight, and risk of neonatal intensive care unit necessity than DET. e-SET of embryos at the cleavage stage reduces the likelihood of live birth by 38% and multiple birth by 94%. Evidence from randomized, controlled trials suggests that increasing the number of e-SET attempts (fresh and/or frozen) results in a cumulative live birth rate similar to that of DET.
The usage of single embryo transfer is highest in Sweden (69.4%), but as low as 2.8% in the USA. Access to public funding for ART, availability of good cryopreservation facilities, effective education about the risks of multiple pregnancy, and legislation appear to be the most important factors for regional usage of single embryo transfer. Also, personal choice plays a significant role as many subfertile couples have a strong preference for twins. | 1 | Biochemistry |
The dominant use for sulfuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as:
Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.
Sulfuric acid is also important in the manufacture of dyestuffs solutions. | 7 | Physical Chemistry |
When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases, the term crystalline finds identical usage to that used in conventional crystallography. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency. | 7 | Physical Chemistry |
Reflection high energy electron diffraction (RHEED), is a technique used to characterize the surface of crystalline materials by reflecting electrons off a surface. As illustrated for the Ewald sphere construction in Figure 22, it uses mainly the higher-order Laue zones which have a reflection component. An experimental diffraction pattern is shown in Figure 23 and shows both rings from the higher-order Laue zones and streaky spots. RHEED systems gather information only from the surface layers of the sample, which distinguishes RHEED from other materials characterization methods that also rely on diffraction of electrons. Transmission electron microscopy samples mainly the bulk of the sample, although in special cases it can provide surface information. Low-energy electron diffraction (LEED) is also surface sensitive, and achieves surface sensitivity through the use of low energy electrons. The main uses of RHEED to date have been during thin film growth, as the geometry is amenable to simultaneous collection of the diffraction data and deposition. It can, for instance, be used to monitor surface roughness during growth by looking at both the shapes of the streaks in the diffraction pattern as well as variations in the intensities. | 7 | Physical Chemistry |
6-Hydroxymelatonin (6-OHM) is a naturally occurring, endogenous, major active metabolite of melatonin. Similar to melatonin, 6-OHM is a full agonist of the MT and MT receptors. It is also an antioxidant and neuroprotective, and is even more potent in this regard relative to melatonin. | 1 | Biochemistry |
Private members include individuals such as researchers, scientists, industrial practitioners, journalists or professors with extensive expertise, passion or active in fields related to the refrigeration sector. | 7 | Physical Chemistry |
The CD 4+ cells through their T cell receptor-CD3 complex recognize the epitope-bound MHC II molecules on the surface of the antigen presenting cells, and get activated. Upon this activation, these T cells proliferate and differentiate into T1 or T2 cells. This makes them produce soluble chemical signals that promote their own survival. However, another important function that they carry out is the stimulation of B cell by establishing direct physical contact with them. | 1 | Biochemistry |
Many structural domains have been conserved through evolution, as prokaryotic initiation factors share similar structures with eukaryotic factors. The prokaryotic initiation factor, IF3, assists with start site specificity, as well as mRNA binding. This is in comparison with the eukaryotic initiation factor, eIF1, who also performs these functions. The elF1 structure is similar to the C-terminal domain of IF3, as they each contain a five-stranded beta sheet against two alpha helices.
The prokaryotic initiation factors IF1 and IF2 are also homologs of the eukaryotic initiation factors eIF1A and eIF5B. IF1 and eIF1A, both containing an OB-fold, bind to the A site and assist in the assembly of initiation complexes at the start codon. IF2 and eIF5B assist in the joining of the small and large ribosomal subunits. The eIF5B factor also contains elongation factors. Domain IV of eIF5B is closely related to the C-terminal domain of IF2, as they both consist of a beta-barrel. The elF5B also contains a GTP-binding domain, which can switch from an active GTP to an inactive GDP. This switch helps to regulate the affinity of the ribosome for the initiation factor.
A eukaryotic initiation factor eIF3 plays an important role in translational initiation. It has a complex structure, composed of 13 subunits. It helps to create the 43S pre-initiation complex, composed of the small 40S subunit attached to other initiation factors. It also helps to create the 48S pre-initiation complex, consisting of the 43S complex with the mRNA. The eIF3 factor can also be used post-translation in order to separate the ribosomal complex and keep the small and large subunits apart. The initiation factor interacts with the eIF1 and eIF5 factors used for scanning and selection of the start codons. This can create changes in the selection of the factors, binding to different codons.
Another important eukaryotic initiation factor, eIF2, binds the tRNA containing methionine to the P site of the small ribosome. The P site is where the tRNA carrying an amino acid forms a peptide bond with the incoming amino acids and carries the peptide chain. The factor consists of an alpha, beta, and gamma subunit. The eIF2 gamma subunit is characterized by a GTP-binding domain and beta-barrel folds. It binds to the tRNA through GTP. Once the initiation factor helps the tRNA bind, the GTP hydrolyzes and is released the eIF2. The eIF2 beta subunit is identified by its Zn-finger. The eIF2 alpha subunit is characterized by an OB-fold domain and two beta strands. This subunit helps to regulate translation, as it becomes phosphorylated to inhibit protein synthesis.
The eIF4F complex supports the cap-dependent translation initiation process and is composed of the initiation factors eIF4A, eIF4E, and eIF4G. The cap end of the mRNA, being the 5’ end, is brought to the complex where the 43S ribosomal complex can bind and scan the mRNA for the start codon. During this process, the 60S ribosomal subunit binds and the large 80S ribosomal complex is formed. The eIF4G plays a role, as it interacts with the polyA-binding protein, attracting the mRNA. The eIF4E then binds the cap of the mRNA and the small ribosomal subunit binds to the eIF4G to begin the process of creating the 80S ribosomal complex. The eIF4A works to make this process more successful, as it is a DEAD box helicase. It allows for the unwinding of the untranslated regions of the mRNA to allow for ribosomal binding and scanning. | 1 | Biochemistry |
The metabolome refers to the complete set of small-molecule chemicals found within a biological sample. The biological sample can be a cell, a cellular organelle, an organ, a tissue, a tissue extract, a biofluid or an entire organism. The small molecule chemicals found in a given metabolome may include both endogenous metabolites that are naturally produced by an organism (such as amino acids, organic acids, nucleic acids, fatty acids, amines, sugars, vitamins, co-factors, pigments, antibiotics, etc.) as well as exogenous chemicals (such as drugs, environmental contaminants, food additives, toxins and other xenobiotics) that are not naturally produced by an organism.
In other words, there is both an endogenous metabolome and an exogenous metabolome. The endogenous metabolome can be further subdivided to include a "primary" and a "secondary" metabolome (particularly when referring to plant or microbial metabolomes). A primary metabolite is directly involved in the normal growth, development, and reproduction. A secondary metabolite is not directly involved in those processes, but usually has important ecological function. Secondary metabolites may include pigments, antibiotics or waste products derived from partially metabolized xenobiotics. The study of the metabolome is called metabolomics. | 1 | Biochemistry |
Quinapril inhibits angiotensin converting enzyme, an enzyme which catalyses the formation of angiotensin II from its precursor, angiotensin I. Angiotensin II is a powerful vasoconstrictor and increases blood pressure through a variety of mechanisms. Due to reduced angiotensin production, plasma concentrations of aldosterone are also reduced, resulting in increased excretion of sodium in the urine and increased concentrations of potassium in the blood. | 4 | Stereochemistry |
An ion-sensitive field-effect transistor (ISFET) is a field-effect transistor used for measuring ion concentrations in solution; when the ion concentration (such as H, see pH scale) changes, the current through the transistor will change accordingly. Here, the solution is used as the gate electrode. A voltage between substrate and oxide surfaces arises due to an ion sheath. It is a special type of MOSFET (metal–oxide–semiconductor field-effect transistor), and shares the same basic structure, but with the metal gate replaced by an ion-sensitive membrane, electrolyte solution and reference electrode. Invented in 1970, the ISFET was the first biosensor FET (BioFET).
The surface hydrolysis of Si–OH groups of the gate materials varies in aqueous solutions due to pH value. Typical gate materials are SiO, SiN, AlO and TaO.
The mechanism responsible for the oxide surface charge can be described by the site binding model, which describes the equilibrium between the Si–OH surface sites and the H ions in the solution. The hydroxyl groups coating an oxide surface such as that of SiO can donate or accept a proton and thus behave in an amphoteric way as illustrated by the following acid-base reactions occurring at the oxide-electrolyte interface:
:—Si–OH + HO ↔ —Si–O + HO
:—Si–OH + HO ↔ —Si–OH + HO
An ISFETs source and drain are constructed as for a MOSFET. The gate electrode is separated from the channel by a barrier which is sensitive to hydrogen ions and a gap to allow the substance under test to come in contact with the sensitive barrier. An ISFETs threshold voltage depends on the pH of the substance in contact with its ion-sensitive barrier. | 7 | Physical Chemistry |
The z-average molar mass is the third moment or third power average molar mass, which is calculated by
The z-average molar mass can be determined with ultracentrifugation. The melt elasticity of a polymer is dependent on . | 7 | Physical Chemistry |
The DNA base editors, developed at Harvard University under David Liu, allow altering the genomic structure of DNA. The base editors include BE3, BE4 and ABE7.
BE3 and its later version, BE4 allow to change the nucleobase C to T and nucleobase G to A. ABE7 allows to change A-T base pairs into G-C base pairs. The system works by rearranging the atoms in the target base pair and then tricking cells into fixing the other DNA strand to make the change permanent. | 1 | Biochemistry |
Observations at the site have led scientists to believe that the area was flooded with water a number of times and was subjected to evaporation and desiccation. In the process sulfates were deposited. After sulfates cemented the sediments, hematite concretions grew by precipitation from groundwater. Some sulfates formed into large crystals which later dissolved to leave vugs. Several lines of evidence point toward an arid climate in the past billion years or so, but a climate supporting water, at least for a time, in the distant past. | 9 | Geochemistry |
Meteorin-like/Meteorin-Beta (Metrnl)/IL-41, also known as subfatin and cometin, is a small (~27kDa) secreted cytokine, protein encoded by a gene called meteorin-like (METRNL). METRNL is highly expressed in mucosal tissues, skin and activated macrophages.
Metrnl has also been described to be a hormone
A screen of human skin-associated diseases showed significant over-expression of METRNL in psoriasis, prurigo nodularis, actinic keratosis and atopic dermatitis. METRNL is also up-regulated in synovial membranes of human rheumatoid arthritis.
Adipocyte Metrnl antagonizes obesity-induced insulin resistance by improving adipose function, including adipocyte differentiation, metabolism activation, and inflammation inhibition Lower serum levels of Metrnl might be a risk factor for developing coronary artery disease and type 2 diabetes mellitus | 1 | Biochemistry |
Sinking oceanic particles encompass a wide range of shape, porosity, ballast and other characteristics. The model shown in the diagram at the right attempts to capture some of the predominant features that influence the shape of the sinking flux profile (red line).
The sinking of organic particles produced in the upper sunlit layers of the ocean forms an important limb of the oceanic biological pump, which impacts the sequestration of carbon and resupply of nutrients in the mesopelagic ocean. Particles raining out from the upper ocean undergo remineralization by bacteria colonized on their surface and interior, leading to an attenuation in the sinking flux of organic matter with depth. The diagram illustrates a mechanistic model for the depth-dependent, sinking, particulate mass flux constituted by a range of sinking, remineralizing particles.
Marine snow varies in shape, size and character, ranging from individual cells to pellets and aggregates, most of which is rapidly colonized and consumed by heterotrophic bacteria, contributing to the attenuation of the sinking flux with depth. | 9 | Geochemistry |
Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula and structure . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium salt of the 12-carbon organosulfate. Its hydrocarbon tail combined with a polar "headgroup" give the compound amphiphilic properties that make it useful as a detergent. SDS is also component of mixtures produced from inexpensive coconut and palm oils. SDS is a common component of many domestic cleaning, personal hygiene and cosmetic, pharmaceutical, and food products, as well as of industrial and commercial cleaning and product formulations. | 1 | Biochemistry |
Yoon was born in Montreal, Quebec and grew up in Blacksburg, VA. As an undergraduate at Harvard University, he became fascinated by organic chemistry working in the laboratories of leading experts in contemporary asymmetric synthesis. Specifically, Yoon first experienced research in David A. Evans's lab studying stereocontrolled aldol reactions.
After earning his A.B. in chemistry from Harvard in 1996, he proceeded to earn his M.S. under the guidance of Erick M. Carreira, who introduced Yoon to synthesis of complex natural products through applied photochemistry. Yoon was then accepted as Dave MacMillan's first graduate student, initially at UC Berkeley and later at Caltech, where he earned his Ph.D. investigating methods to control the stereochemistry of pericyclic reactions. He returned to Harvard in 2002 as a postdoc to research the use of hydrogen bonding urea catalysts in asymmetric synthesis in the laboratory of Eric Jacobsen. | 0 | Organic Chemistry |
Cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology, and to derive medications.The techniques by which cells are studied have evolved. Due to advancements in microscopy, techniques and technology have allowed scientists to hold a better understanding of the structure and function of cells. Many techniques commonly used to study cell biology are listed below:
* Cell culture: Utilizes rapidly growing cells on media which allows for a large amount of a specific cell type and an efficient way to study cells. Cell culture is one of the major tools used in cellular and molecular biology, providing excellent model systems for studying the normal physiology and biochemistry of cells (e.g., metabolic studies, aging), the effects of drugs and toxic compounds on the cells, and mutagenesis and carcinogenesis. It is also used in drug screening and development, and large scale manufacturing of biological compounds (e.g., vaccines, therapeutic proteins).
* Fluorescence microscopy: Fluorescent markers such as GFP, are used to label a specific component of the cell. Afterwards, a certain light wavelength is used to excite the fluorescent marker which can then be visualized.
* Phase-contrast microscopy: Uses the optical aspect of light to represent the solid, liquid, and gas-phase changes as brightness differences.
* Confocal microscopy: Combines fluorescence microscopy with imaging by focusing light and snap shooting instances to form a 3-D image.
* Transmission electron microscopy: Involves metal staining and the passing of electrons through the cells, which will be deflected upon interaction with metal. This ultimately forms an image of the components being studied.
* Cytometry: The cells are placed in the machine which uses a beam to scatter the cells based on different aspects and can therefore separate them based on size and content. Cells may also be tagged with GFP-fluorescence and can be separated that way as well.
* Cell fractionation: This process requires breaking up the cell using high temperature or sonification followed by centrifugation to separate the parts of the cell allowing for them to be studied separately. | 1 | Biochemistry |
The Energy Independence and Security Act of 2007 calls for the production of of renewable fuels by 2022, including of corn-based ethanol, a tripling of current production that would require a similar increase in corn production. Unfortunately, the plan poses a new problem; the increase in demand for corn production results in a proportional increase in nitrogen runoff. Although nitrogen, which makes up 78% of the Earth's atmosphere, is an inert gas, it has more reactive forms, two of which (nitrate and ammonia) are used to make fertilizer.
According to , a professor of crop physiology at the University of Illinois at Urbana-Champaign, corn requires more nitrogen-based fertilizer because it produces a higher grain per unit area than other crops and, unlike other crops, corn is completely dependent on available nitrogen in soil. The results, reported March 18, 2008, in Proceedings of the National Academy of Sciences, showed that scaling up corn production to meet the goal would increase nitrogen loading in the Dead Zone by 10–18%. This would boost nitrogen levels to twice the level recommended by the Mississippi Basin/Gulf of Mexico Water Nutrient Task Force (Mississippi River Watershed Conservation Programs), a coalition of federal, state, and tribal agencies that have monitored the dead zone since 1997. The task force says a 30% reduction of nitrogen runoff is needed if the dead zone is to shrink. | 9 | Geochemistry |
Extra-thyroidal iodine exists in several other organs, including the mammary glands, eyes, gastric mucosa, cervix, cerebrospinal fluid, arterial walls, ovary and salivary glands. In the cells of these tissues the iodide ion (I) enters directly by the sodium-iodide symporter (NIS). Different tissue responses for iodine and iodide occur in the mammary glands and the thyroid gland of rats. The role of iodine in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is not well known. It has been shown to act as an antioxidant and antiproliferant in various tissues that can uptake iodine. Molecular iodine (I) has been shown to have a suppressive effect on benign and cancerous neoplasias.
The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others. | 1 | Biochemistry |
Different genotypes may compete with each other in a way that is not beneficial for the population. A pure line optimized for a certain environment or usage outperforms the CCP under these specific conditions.
There is no reason to believe that the Darwinian selection will work in the desired direction for traits such as baking quality. Natural selection and in-field human selection act on the plant stage, not the seed stage.
Common Bunt is a seed borne disease in wheat. In conventional farming it is controlled by fungicide treatment of seeds. In organic farming seeds can be cleaned by brushing before sowing, but it is also desirable that plants have genetic resistance. A CCP, including crosses of resistant cultivars, was grown with heavy common bunt infection for 5 years and it appeared to get more resistant, but the common bunt's virulence appeared to change at least as fast. The overall result was that infection levels went up. | 1 | Biochemistry |
Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%; however, the surface temperature of the planet has remained within the levels of habitability, reaching quite regular low and high margins. Lovelock has also hypothesised that methanogens produced elevated levels of methane in the early atmosphere, giving a situation similar to that found in petrochemical smog, similar in some respects to the atmosphere on Titan. This, he suggests, helped to screen out ultraviolet light until the formation of the ozone layer, maintaining a degree of homeostasis. However, the Snowball Earth research has suggested that "oxygen shocks" and reduced methane levels led, during the Huronian, Sturtian and Marinoan/Varanger Ice Ages, to a world that very nearly became a solid "snowball". These epochs are evidence against the ability of the pre Phanerozoic biosphere to fully self-regulate.
Processing of the greenhouse gas CO, explained below, plays a critical role in the maintenance of the Earth temperature within the limits of habitability.
The CLAW hypothesis, inspired by the Gaia hypothesis, proposes a feedback loop that operates between ocean ecosystems and the Earths climate. The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative feedback loop that acts to stabilise the temperature of the Earths atmosphere.
Currently the increase in human population and the environmental impact of their activities, such as the multiplication of greenhouse gases may cause negative feedbacks in the environment to become positive feedback. Lovelock has stated that this could bring an extremely accelerated global warming, but he has since stated the effects will likely occur more slowly. | 9 | Geochemistry |
The light chain gene has three gene segments. These include: the light chain variable region (V), joining region (J), and constant region (C) gene segments. The variable region of light is therefore encoded by the rearrangement of VJ segments. The light chain can be either kappa,κ or lambda,λ. This process takes place at the level of mRNAs processing. Random rearrangements and recombinations of the gene segments at DNA level to form one kappa or lambda light chain occurs in an orderly fashion. As a result, "a functional variable region gene of a light chain contains two coding segments that are separated by a non-coding DNA sequence in unrearranged germ-line DNA" (Barbara et al., 2007). | 1 | Biochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.