Peptidoglykanu

Peptidoglykanu is the structural polymer that forms the cell wall of most bacteria. It consists of long glycan chains made of repeating disaccharide units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Each NAM residue bears a short, cross-linking peptide stem that varies among species. These glycan strands are connected by peptide cross-links, which give the wall its rigidity and resilience.

In Gram-positive bacteria, peptidoglykanu forms a thick, multilayered layer outside the cytoplasmic membrane, often accompanied by teichoic acids. In Gram-negative bacteria, a thinner peptidoglykanu layer resides in the periplasm between the inner and outer membranes, with cross-linking typically less dense and the outer membrane contributing to barrier function.

Biosynthesis occurs in stages: cytoplasmic synthesis of NAM-pentapeptide, linkage to a lipid carrier (undecaprenyl phosphate) to form lipid II, transport across the cytoplasmic membrane by flippases, extracellular polymerization by glycosyltransferases (transglycosylation), and cross-linking by penicillin-binding proteins (transpeptidation). Remodeling enzymes such as autolysins balance synthesis and degradation to allow growth and division.

Functionally, the peptidoglykanu mesh provides cell shape and rigidity, protects against osmotic lysis, and serves as a scaffold for other wall components. It is a major target for antibiotics: beta-lactams inhibit transpeptidases, while glycopeptides bind the D-Ala-D-Ala terminus to block elongation. Resistance can involve altered targets, reduced permeability, or enzymes that modify precursors or detach inhibitors.

Peptidoglykanu is absent in many archaea and some intracellular bacteria, while its basic architecture is conserved across most bacterial lineages, underscoring its essential role in bacterial physiology.