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#peptidoglycan

9 public questions tagged with this topic.

Microbial Physiology

Which type of bond in peptidoglycan is hydrolyzed by lysozyme?

Peptidoglycan glycan backbone consists of repeating beta-linked disaccharide where N-acetylglucosamine and N-acetylmuramic acid are joined via beta-1,4 glycosidic bonds between C1 of one sugar and C4 of other, creating long linear strands that run roughly perpendicular to cell long axis. This beta-1,4 linkage creates specific geometry recognized by lysozyme, a muramidase ubiquitous in innate immunity found in tears, saliva, egg white, and macrophage granules. Lysozyme's active site cleft accommodates hexasaccharide, distorts MurNAc residue into half-chair conformation, and catalyzes hydrolysis

Ref: Vollmer et al., FEMS Microbiol Rev 2008, Lysozyme Specificity; Callewaert & Michiels, J Biosci 2010, Muramidases.

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Microbial Physiology

The pentapeptide bridge in Gram-positive bacteria consists mainly of:

Crosslinking between glycan strands in many Gram-positive pathogens involves pentaglycine bridge characteristic of Staphylococcus aureus, intensively studied because it influences vancomycin sensitivity. After polymerization, tetrapeptide side chains protrude from MurNAc. In S. aureus, FemXAB family nonribosomal peptidyl transferases add glycine residues one by one to epsilon amino group of L-lysine at position three, using glycyl-tRNA as donor, generating pentaglycine. This flexible extension then becomes substrate for transpeptidase that links glycine terminal to D-alanine of neighboring ste

Ref: Schneider et al., Mol Microbiol 2004, FemABX Pentaglycine; Pinho et al., Nature Rev Microbiol 2013, Staphylococcal Cell Wall.

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Microbial Physiology

Which enzyme is involved in the cross-linking of peptidoglycan?

After glycan polymerization by transglycosylases elongating alternating N-acetylglucosamine and N-acetylmuramic acid strands, final strength requires crosslinking of stem peptides attached to MurNAc. Stem typically comprises L-alanine, D-glutamate, meso-diaminopimelic acid or L-lysine, and terminal D-alanyl-D-alanine dipeptide. DD-transpeptidases, members of penicillin-binding protein family including PBP1a, PBP1b, PBP2a, and PBP3, perform nucleophilic attack where serine in active site forms bond with penultimate D-alanine, releasing terminal D-alanine, then transfers acyl-intermediate to ami

Ref: Vollmer et al., FEMS Microbiol Rev 2008, Peptidoglycan Crosslinking; Lovering et al., Ann Rev Biochem 2012, PBPs.

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Microbial Physiology

Which of the following bacterial cell wall components is absent in Archaea?

Bacterial cell wall architecture includes several hallmark polymers absent in Archaea, reflecting fundamentally different envelope synthesis pathways. Peptidoglycan, composed of alternating N-acetylglucosamine and N-acetylmuramic acid crosslinked by D-amino acid containing peptides, is universal among bacteria but never found in archaea, where pseudomurein or S-layers substitute. Outer membrane containing lipopolysaccharide, characterized by Lipid A endotoxin, core oligosaccharide, and O-antigen, is diagnostic of Gram-negative bacteria and relies on Lpx biosynthetic enzymes absent in archaea.

Ref: Kandler & Konig, Archaea 1998, Bacterial vs Archaeal Walls; Albers & Meyer, Nature Rev Microbiol 2011, Comparative Envelope.

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Microbial Physiology

Which polysaccharide is found in the archaeal cell wall instead of peptidoglycan?

Bacterial cell walls are built on peptidoglycan, a heteropolymer of N-acetylglucosamine and N-acetylmuramic acid crosslinked by peptide bridges sensitive to lysozyme and penicillin. Archaea do not synthesize peptidoglycan; instead, methanogenic euryarchaeota that possess a rigid wall produce pseudomurein, also called pseudopeptidoglycan, which superficially resembles peptidoglycan but differs chemically enough to confer resistance to classical wall antibiotics. Pseudomurein consists of N-acetylglucosamine linked to N-acetyltalosaminuronic acid rather than N-acetylmuramic acid, bearing L-amino

Ref: Albers & Meyer, Nature Rev Microbiol 2011, Pseudomurein; Kandler & Konig, Archaea 1998, Cell Walls.

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Carbohydrates

Which of the following is not a component of bacterial cell walls?

Chitin is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Carbohydrates, the other options (Peptidoglycan, N-acetylglucosamine, and N-acetylmuramic acid) are all valid and well-established concepts. Chitin is either unrelated to the topic, describes a different biological process, or represents a common misconception. Questions framed as 'which is NOT' require students to identify the exception among otherwise correct statements, demanding comprehensive knowledge of the topic rather than recognition of a single

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 7

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Carbohydrates

Which sugar derivative is a component of bacterial peptidoglycan?

N-acetylmuramic acid is the correct answer as it accurately identifies the biological location, composition, or distribution described in this question. In Carbohydrates, the spatial organization and localization of molecules are critical to their function. N-acetylmuramic acid is specifically associated with the structure or compartment mentioned because of its unique biochemical properties and physiological role. The other options (Dihydroxyacetone, Trehalose, and Amylopectin) are primarily associated with different cellular compartments, tissues, or structural contexts.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 7

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Carbohydrates

Which polysaccharide is the main component of bacterial cell walls?

Peptidoglycan is the correct answer as it accurately identifies the biological location, composition, or distribution described in this question. In Carbohydrates, the spatial organization and localization of molecules are critical to their function. Peptidoglycan is specifically associated with the structure or compartment mentioned because of its unique biochemical properties and physiological role. The other options (Chitin, Glycogen, and Dextran) are primarily associated with different cellular compartments, tissues, or structural contexts.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 7

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