Cytoplasmic membrane, bacterial functions

Many kinds of bacterial cells contain integrated protein complexes that take part in the respiratory electron-transport reaction in the cytoplasmic membrane. It is located near the cell surface beneath the cell wall, which is permeable to substances of relatively low molecular weights. Thus, oxidoreductases existing in the periplasmic space or bound to the cytoplasmic membrane may function as catalysts to oxidize or reduce substances outside the cells using externally added artificial electron acceptors or donors. A scheme of the bacterial cell catalysis is illustrated in Fig. 18. The rate (vceii) of the bacterial cell-catalyzed reaction can be written as (47)... 

Saurin, W., Koster, W. and Dassa, E. (1994). Bacterial binding protein-dependent permeases characterization of distinctive signatures for functionally related integral cytoplasmic membrane proteins, Mol. Microbiol., 12, 993-1004. 

Compartmentalization allows cells to retain and organize the vast array of solutes and macromolecules required for life. However, life depends equally on the capacity of the cell for selective movement of molecules between distinct compartments. For example, a significant subset of proteins must be translocated from their site of synthesis in the cytoplasm, across one or more membranes, to reach their final functional destination within a topologically distinct compartment. Irrespective of the target membrane (endoplasmic reticulum, mitochondrial outer membrane, bacterial cytoplasmic membrane, etc.), translocation generally requires that the protein destined for translocation contains a cis-acting targeting element that directs it to the proper membrane. 

The integrity of the cytoplasmic membrane is vital for the normal functioning of all cells. Bacterial membranes do not contain sterols and in this... 

The MCPs fulfill at least three functions in bacterial chemotaxis they bind the ligands (or sense changes in the ambient temperature and pH), they transduce the chemotactic signal across the cytoplasmic membrane, and, as part of their involvement in adaptation, they undergo methylation or demethylation. The focus here will be on Tar, which is the best-characterized MCP. 

The selectivity of the tetracyclines, so much used in treating bacterial infections in mammals, depends on a similarly favourable distribution the bacteria concentrate these antibiotics whereas mammalian cells do not. Concentration of tetracyclines by bacteria (both Gram-positive and -negative types) was found to be a function of the cytoplasmic membrane (Franklin, 1971). Because of this difference, tetracyclines inhibit ribosomal protein synthesis in bacteria at doses which do not affect it in higher organisms (Franklin, 1963b, 1966). This selectivity depends on the intactness of the mammalian cell membrane, because isolated ribosomes (rat liver was used) were found to be as subject to inhibition of protein synthesis as bacterial ones were (Franklin, 1963a Section 11.8). 

Besides the mechanisms described above, some orgartic adds (especially sorbic but also lactic acid) can act by chelating ions from the medium as well as from bacterial cell walls, thus affecting both microbial function and structure (Stratford, 1999). Moreover, the lipophilic nature of acetic and lactic acids can also account for possible damage to the structure of the cytoplasmic membrane of target microorganisms, which interferes with its fluidity and regular functionahty (Hirshfield et al., 2003 Strafford, 1999). 

The cytoplasmic membrane, or plasma membrane is a phospholipid bilayer into which proteins/enzymes are embedded. The function of the cytoplasmic membrane is to act as a selective permeability barrier between the cytoplasm and the exterior environment. A mesosome is an organelle of bacteria that appears as an invagination of the plasma membrane and functions either in DNA replication and cell division, energy production, or excretion of exoenzymes. Flagella (if present) originate in a special structure in the cytoplasmic membrane (see the section on Flagella under Structure of the Bacterial Cell). 

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