Peptidoglycan cell wall

C. trachomatis possesses characteristics resembling both bacteria and viruses. Its major membrane is comparable to that of gram-negative bacteria, although it lacks a peptidoglycan cell wall and requires cellular components from the host for replication. Chlamydia transmission risk is thought to be less than that of gonorrhea. 

In addition to transpeptidases, other penicillin-binding proteins (PBPs) function as transglycosylases and carboxypeptidases. All of the PBPs are involved with assembly, maintenance, or regulation of peptidoglycan cell wall synthesis. When (3-lactam antibiotics inactivate PBPs, the consequence to the bacterium is a structurally weakened cell wall, aberrant morphological form, cell lysis, and death. 

Peptidoglycan (cell wall) (b) Gram-negative bacteria... 

Beta-lactam penicillins prevent the biosynthesis of a dipeptidoglycan which forms the peptidoglycan cell wall in bacteria. This results in cell death and bactericidal activity. Specifically, they acylate a specific bacterial D-transpeptidase, which inactivates this enzyme and it therefore cannot form peptide crosslinks of two linear peptidoglycan strands for cell wall formation. 

A-acetylglucosamine, providing the necessary carboxylate anchor for attachment of the pentapeptide required for bacterial peptidoglycan (cell wall) formation. Bacteria that encode a MurA orthologue where the susceptible Cys is replaced by an Asp (e.g., Mycobacteria) are intrinsically genetically resistant to fosfomycin (Fig. 1) (11, 12). 

Gram-positive bacteria contain a rigid peptidoglycan cell wall surrounding the cytoplasmic membrane. Gram-negative bacteria contain an additional third, outer layer. This wall is a complex structure with lipoproteins and lipopolysaccharides. Synthesis of two outer walls from different bacterial cells is described in this concept screen ... 

Differences between bacteria and human cells. Different species of bacteria have some common structural features that distinguish them from animal cells. They are single-cell organisms that are prokaryotes ( before nucleus ). Their genetic material (DNA) is concentrated in the central region of the cell called a nucleoid, rather than a nucleus, because it is not separated from the rest of the cellular contents by a membrane. Likewise, bacteria contain no cytoplasmic organelles defined by membranes. They do have a plasma membrane that encloses the cytoplasm. External to this membrane is a peptidoglycan cell wall composed of extensively cross-linked polysaccharides that form a protective shield on the surface of the cell. 

Penicillins and cephalosporins specifically inhibit late stages of the enzymatic construction of the bacterial peptidoglycan cell wall component, a network of peptides and polysaccharides. Since mammalian cells do not possess such a cell wall, the jS-lactam antibiotics are very specific and virtually non-toxic. This ideal property is not shared by other bactericidal substances, which impair or prevent growth of microorganisms by other, less specific, reaction mechanisms. This is true, e.g. for compounds affecting ion transport in lipid membranes. 

The archaebacteria differ from eubacteria in that they lack muramic acid and therefore a peptidoglycan cell wall [6,7], their membrane lipids are based on ether linkages, rather than ester linkages [8-11] and they differ in intermediary metabolism and coenzyme complement [12,13]. The differences between archaebacteria and eubacteria imply that the former are a source of unique enzymes, but so far only a few of these have been studied (see below). 

Of the standard a-amino acids, all but glycine can exist in either of two optical isomers, called L or D amino acids, which are mirror images of each other. While L-amino acids represent all of the amino acids found in proteins during translation in the ribosome, D-amino acids are found in some proteins produced by enzyme posttranslational modifications after translation and translocation to the endoplasmic reticulum, as in exotic sea-dwelling organisms such as cone snails. They are also abundant components of the peptidoglycan cell walls of bacteria, and D-serine may act as a neurotransmitter in the brain. The L and D convention for amino acid configuration refers not to the optical... 

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