Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A): Peptidoglycan-containing bacterial cell wall is resistant to hydrolytic action of many proteases.
Reason (R): The presence of D-amino amino acids in the peptidoglycan structure of bacterial cell wall makes it resistant to most proteases.

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

While bacterial cell walls resist proteases due to D-amino acids, they remain susceptible to the enzyme lysozyme, which hydrolyzes the \(\beta\)-(1,4) glycosidic bonds between NAG and NAM sugars rather than peptide bonds.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bacterial cell walls consist of peptidoglycan (murein), which provides structural rigidity and protection against environmental stresses and enzymatic attack.

Step 2: Detailed Explanation:
Assertion (A) is correct because the peptidoglycan layer of bacterial cell walls is highly resistant to degradation by many host proteases, which helps the bacteria survive inside host tissues.
Reason (R) is correct because standard ribosomal proteins consist exclusively of L-amino acids, and most eukaryotic proteases are stereospecific, cleaving peptide bonds only between L-isomers.
Peptidoglycan contains unique D-amino acids (such as D-alanine and D-glutamic acid) in its cross-linking oligopeptide chains.
Because proteases cannot recognize these D-amino acid stereoisomers, they are unable to cleave the peptidoglycan backbone.
Thus, the presence of D-amino acids directly explains the cell wall's resistance to protease enzymes.

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).