Cell wall constituents synthesis

Park and Strominger noticed the accumulation of a C3didine derivative in cultures of Staphylococcus aureus which had been inhibited by chloramphenicol, penicillin, or Crystal Violet. This cytidine derivative has been identified by Baddiley s group as cytidine ribitol pyrophosphate. Since these inhibitors affect the cell-wall synthesis, the data lend support to the belief that the cytidine compound is involved in the biosynthesis of a cell-wall constituent, and a likely candidate would be ribitol teichoic acid. 

The C2 pool, which is also part of glycolytic breakdown, is the starting point for lipid synthesis. In contrast, amino acids have several precursors and they are connected to a range of pools and metabolic pathways. To understand the structural and chemical similarity and possible differences between organisms, the following biochemical groups are described more in detail carbohydrates, phenylpropanes and their associated derivatives, amino acids, lipids, and the major cell wall constituents. 

A large number of cellular processes and biosythetic pathways of eukaryotic cells are compartmentalized and restricted to specific membranes. Mitochondria and chloroplasts are two cases in point. In prokaryotic cells, many of the same functions are performed by a single membrane. The transport of metabolites and ions, oxidative phosphorylation, photosynthesis, phospholipid biosynthesis, and the synthesis of cell-wall constituents are a few examples of processes carried out by enzyme systems localized in the bacterial plasma membrane (Chapters... 

The primary cell walls of the meristematic cells have their microfibrils orientated predominantly in a direction transverse to the axis of the root or shoot. When cell expansion occurs there is an increase in cell wall material, a synthesis of cellulose and other cell wall constituents. Expansion at the outer surface of the cell wall causes stretching in the direction of most active cell extension and as this happens the microfibrils become re-orientated more and more along the longitudinal axis of growth. At the same time new layers of wall... 

It should be emphasised that we do not yet fully understand the mechanism whereby cellulose, or hemicelluloses or pectins are synthesised nor do we yet know whether the plant hormones (auxins) promote cell expansion by some direct action on the association together or primary synthesis of cell wall constituents. Furthermore, we do not understand fully what factors determine the regular orientation of microfibrils as laid down in each wall layer. Particularly, during wall thickening in fully expanded cells, the orientation may differ from layer to layer (Fig. 2.23). The pattern for each layer seems to be determined by some pattern established at the cytoplasm-wall interface and which can be revealed prior to the actual development of the new layer of cellulose (Fig. 2.24). 

Cell walls are biochemically rather inert with reduced digestibility to many organisms because of their complex cellulose, pectin, and lignin molecules. Callose and lignin are often accumulated at the site of infection or wounding (6,7) and form a penetration barrier. Synthesis of inhibitory proteins (e.g., lectins, protease inhibitors) or enzymes (e.g., chitinase, lysozyme, hydrolases, nucleases) that could degrade microbial cell walls or other microbial constituents would be protective, as well as synthesis of peroxidase and phe-nolase, which could help inactivate phytotoxins produced by many bacteria and fungi. These proteins are either stored in the vacuole... 

Another interesting antibiotic constmct is a peptide-conjugated form of j8-KDO. jS-KDO is an inhibitor of the CMP-KDO synthetase that is involved in lipopolysaccharide (LPS) synthesis, a major constituent of the bacterial cell wall. Antibacterial activity is thus accomplished by interference with cell wall construction. /3-KDO is incapable of membrane permeation, and therefore is not useful as an antibiotic in its native form. Hammond et al. have shown that conjugation of a /3-KDO analog to certain dipeptides resolves this problem [184] (O Fig. 14). Attachment of the /3-KDO analog to a dipeptide allows the glycopeptide constmct to permeate the bacterial membrane. Inside the cell, proteases hydrolyze the peptide and release the inhibitor, resulting ultimately in bacterial cell death. 

The bacitracins are a mixed group of polypeptide antibiotics. The major constituent is bacitracin A. Bacitracin inhibits cell wall synthesis. A variety of gram-positive cocci and bacilli, Neisseria, H. influenzae, and Treponema pallidum are sensitive to the drug. A unit of the antibiotic is equivalent to 26 pg of the USP standard. 

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