Question:
Peptidoglycan is a complex polymer of sugars and amino acids; the substance from which bacterial cell walls are made. Choose set of correct statements below with respect to peptidoglycan:
(A) A rigid layer of peptidoglycan consist of NAG and NAM which is crosslinked by short peptides
(B) Antibiotics including penicillin does not inhibit peptidoglycan synthesis
(C) Gram positive bacteria contain thick layer of peptidoglycan
(D) Gram negative bacteria have less peptidoglycan
Choose the correct answer from the options given below:
Peptidoglycan is a complex polymer of sugars and amino acids; the substance from which bacterial cell walls are made. Choose set of correct statements below with respect to peptidoglycan:
(A) A rigid layer of peptidoglycan consist of NAG and NAM which is crosslinked by short peptides
(B) Antibiotics including penicillin does not inhibit peptidoglycan synthesis
(C) Gram positive bacteria contain thick layer of peptidoglycan
(D) Gram negative bacteria have less peptidoglycan
Choose the correct answer from the options given below:
(A) A rigid layer of peptidoglycan consist of NAG and NAM which is crosslinked by short peptides
(B) Antibiotics including penicillin does not inhibit peptidoglycan synthesis
(C) Gram positive bacteria contain thick layer of peptidoglycan
(D) Gram negative bacteria have less peptidoglycan
Choose the correct answer from the options given below:
Show Hint
Peptidoglycan = NAG + NAM + Peptide cross-links.
- Thick in Gram-Positive bacteria (retains crystal violet).
- Thin in Gram-Negative bacteria (loses crystal violet).
- Targeted and inhibited by penicillin.
- Thick in Gram-Positive bacteria (retains crystal violet).
- Thin in Gram-Negative bacteria (loses crystal violet).
- Targeted and inhibited by penicillin.
Updated On: Jul 23, 2026
- (A), (B) and (D) only.
- (A), (B) and (C) only.
- (B), (C) and (D) only.
- (A), (C) and (D) only.
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Peptidoglycan (murein) is a unique, essential structural component of the cell wall of most bacteria.
It provides structural strength and maintains osmotic stability.
The structural differences in peptidoglycan between Gram-positive and Gram-negative bacteria are the basis for the Gram-staining technique and influence antibiotic susceptibility.
Step 2: Detailed Explanation:
Let us evaluate each of the given statements:
- Statement (A) is correct. Peptidoglycan is a polymer consisting of alternating residues of \(\beta\)-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
These glycan chains are cross-linked by short tetrapeptide chains attached to NAM, providing a rigid, mesh-like structure.
- Statement (B) is incorrect. Beta-lactam antibiotics, including penicillin, specifically target and inhibit the transpeptidase enzymes (penicillin-binding proteins) that catalyze the cross-linking of these short peptide chains.
By blocking this step, penicillin prevents stable peptidoglycan synthesis, leading to cell wall weakening and osmotic lysis of dividing bacteria.
- Statement (C) is correct. Gram-positive bacteria possess a thick, multi-layered peptidoglycan cell wall (ranging from 20 to 80 nm in thickness), which constitutes up to 90% of the dry weight of their cell wall.
- Statement (D) is correct. Gram-negative bacteria have a much thinner, single-layered peptidoglycan wall (about 7 to 8 nm thick), which makes up only about 10% of their total cell wall structure, sandwiched between the inner and outer membranes.
Therefore, statements (A), (C), and (D) are correct, and Statement (B) is incorrect.
Step 3: Final Answer:
The correct option is (D).
Peptidoglycan (murein) is a unique, essential structural component of the cell wall of most bacteria.
It provides structural strength and maintains osmotic stability.
The structural differences in peptidoglycan between Gram-positive and Gram-negative bacteria are the basis for the Gram-staining technique and influence antibiotic susceptibility.
Step 2: Detailed Explanation:
Let us evaluate each of the given statements:
- Statement (A) is correct. Peptidoglycan is a polymer consisting of alternating residues of \(\beta\)-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
These glycan chains are cross-linked by short tetrapeptide chains attached to NAM, providing a rigid, mesh-like structure.
- Statement (B) is incorrect. Beta-lactam antibiotics, including penicillin, specifically target and inhibit the transpeptidase enzymes (penicillin-binding proteins) that catalyze the cross-linking of these short peptide chains.
By blocking this step, penicillin prevents stable peptidoglycan synthesis, leading to cell wall weakening and osmotic lysis of dividing bacteria.
- Statement (C) is correct. Gram-positive bacteria possess a thick, multi-layered peptidoglycan cell wall (ranging from 20 to 80 nm in thickness), which constitutes up to 90% of the dry weight of their cell wall.
- Statement (D) is correct. Gram-negative bacteria have a much thinner, single-layered peptidoglycan wall (about 7 to 8 nm thick), which makes up only about 10% of their total cell wall structure, sandwiched between the inner and outer membranes.
Therefore, statements (A), (C), and (D) are correct, and Statement (B) is incorrect.
Step 3: Final Answer:
The correct option is (D).
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