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Questions and Answers
What is a unique feature of almost all prokaryotic cells related to their cell structure?
What is a unique feature of almost all prokaryotic cells related to their cell structure?
- Cell wall peptidoglycan (correct)
- Chloroplasts for photosynthesis
- Mitochondria for energy production
- Presence of nuclear membrane
Which component is involved in the cross-linking of peptidoglycan in bacterial cell walls?
Which component is involved in the cross-linking of peptidoglycan in bacterial cell walls?
- L-isoglutamic acid
- Muramic acid
- D-alanine
- L-lysine (correct)
What distinguishes the peptidoglycan structure of S. aureus from that of E. coli?
What distinguishes the peptidoglycan structure of S. aureus from that of E. coli?
- Higher cross-linking (correct)
- Less open mesh structure
- Absence of disaccharides
- The presence of teichoic acids
Which amino acid is uniformly present in Gram-negative peptidoglycans for cross-linking?
Which amino acid is uniformly present in Gram-negative peptidoglycans for cross-linking?
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The glycan backbone of peptidoglycans consists of repeating groups of which disaccharide?
The glycan backbone of peptidoglycans consists of repeating groups of which disaccharide?
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Study Notes
Prokaryotic Cell Walls
- Peptidoglycan is a defining feature of most prokaryotic cell walls, with exceptions being Halobacterium halobium and mycoplasmas.
- Peptidoglycan biosynthesis enzymes serve as targets for antibiotics, inhibiting peptidoglycan synthesis.
- Peptidoglycan consists of a repeating disaccharide backbone of N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) linked by β1,4 glycosidic bonds.
- Tetrapeptides are attached to MurNAc residues, consisting of L-alanine-D-isoglutamic acid-L-lysine (or diaminopimelic acid)-D-alanine.
- Cross-linking occurs between tetrapeptides, either directly or via a peptide bridge.
- In Staphylococcus aureus, a glycine pentapeptide bridge links adjacent peptide structures, resulting in high cross-linking.
- Escherichia coli has a less cross-linked peptidoglycan structure, leading to a more open mesh.
- Diaminopimelic acid or lysine serves as the ε-amino group for cross-linking, consistently found in Gram-negative bacteria.
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