bacterial cell walls are made rigid by the presence of hydraulic turgor pressure.
bacterial cell walls are made rigid by the presence of?
hydraulic turgor pressure
the cell envelope is composed of the plasma membrane and cell wall. as in other organisms, the bacterial cell wall provides structural integrity to the cell. in prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor pressure caused by the much higher concentrations of proteins and other molecules inside the cell compared to its external environment. the bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan which is located immediately outside of the cytoplasmic membrane. peptidoglycan is made up of a polysaccharide backbone consisting of alternating n-acetylmuramic acid (nam) and n-acetylglucosamine (nag) residues in equal amounts. peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. it is relatively porous and is not considered to be a permeability barrier for small substrates. while all bacterial cell walls (with a few exceptions e.g. extracellular parasites such as "mycoplasma") contain peptidoglycan, not all cell walls have the same overall structures. since the cell wall is required for bacterial survival, but is absent in some eukaryotes, several antibiotics (notably the penicillins and cephalosporins) stop bacterial infections by interfering with cell wall synthesis, while having no effects on human cells which have no cell wall, only a cell membrane. there are two main types of bacterial cell walls, those of gram-positive bacteria and those of gram-negative bacteria, which are differentiated by their gram staining characteristics. for both these types of bacteria, particles of approximately 2 nm can pass through the peptidoglycan. if the bacterial cell wall is entirely removed, it is called a protoplast while if it's partially removed, it is called a spheroplast. "β"-lactam antibiotics such as penicillin inhibit the formation of peptidoglycan cross-links in the bacterial cell wall. the enzyme lysozyme, found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.
bacterial cell structure
"penetration" follows attachment: virions enter the host cell through receptor-mediated endocytosis or membrane fusion. this is often called viral entry. the infection of plant and fungal cells is different from that of animal cells. plants have a rigid cell wall made of cellulose, and fungi one of chitin, so most viruses can get inside these cells only after trauma to the cell wall. nearly all plant viruses (such as tobacco mosaic virus) can also move directly from cell to cell, in the form of single-stranded nucleoprotein complexes, through pores called plasmodesmata. bacteria, like plants, have strong cell walls that a virus must breach to infect the cell. given that bacterial cell walls are much thinner than plant cell walls due to their much smaller size, some viruses have evolved mechanisms that inject their genome into the bacterial cell across the cell wall, while the viral capsid remains outside.
virus