exocytosis packages protein for transport out of the cell.
packages protein for transport out of the cell?
exocytosis
the term secretome was coined by tjalsma and colleagues to denote all the factors secreted by a cell, along with the secretory pathway constituents. this definition of secretome was revised to include only proteins secreted into the extracellular space. the secreted proteins in humans account for 13–20% of the entire proteome and include growth factors, chemokines, cytokines, adhesion molecules, proteases and shed receptors. human protein-coding genes (39%, 19613 genes) are predicted to have either a signal peptide and/or at least one transmembrane region suggesting active transport of the corresponding protein out of the cell (secretion) or location in one of the numerous membrane systems in the cell. increasing evidence showed that, in addition to the protein cargo, non-protein components, such as lipid, micro-rnas and messenger-rna, could also be secreted by cells via both microvesicles (100–1000 nm diameter) − shedding from the plasma membrane − and exosomes (30–150 nm diameter) − released via endosomal-exocytosis event. factors present in both these organelles accounts for up to 42% of the secretome and have been incorporated as the collective secretome. there is a vast array of methodologies available to study cell secretomes of plant cells, mammalian cells, stem cells and cancer cells.
secretome
mediated transport refers to transport mediated by a membrane transport protein. substances in the human body may be hydrophobic, electrophilic, contain a positively or negatively charge, or have another property. as such there are times when those substances may not be able to pass over the cell membrane using protein-independent movement. the cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. there are three types of mediated transport: uniport, symport, and antiport. things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell. one example of a uniport mediated transport protein is glut1. glut1 is a transmembrane protein, which means it spans the entire width of the cell membrane, connecting the extracellular and intracellular region. it is a uniport system because it specifically transports glucose in only one direction, down its concentration gradient across the cell membrane. an example of a symport mediated transport protein is sglt1, a sodium/glucose co-transporter protein that is mainly found in the intestinal tract. the sglt1 protein is a symport system because it passes both glucose and sodium in the same direction, from the lumen of the intestine to inside the intestinal cells. an example of an antiport mediated transport protein is the sodium-calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. this transport protein is an antiport system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which is transported in the opposite direction.
mediated transport