USMLE 2 Question 21

An enzyme found in tears and saliva is known to damage bacterial cell walls.

It does this by:

a) dissolving the cytoplasmic membrane
b) breaking the covalent links between teichoic acid and muramic acid
c) hydrolyzing the link between N-acetyl glucosamine and N-acetyl muramic acid
d) inhibiting cell wall protein synthesis
e) converting D-alanine to L-alanine








ANSWER
The correct answer is C



Explanation
The correct answer is c) hydrolyzing the link between N-acetyl glucosamine and N-acetyl muramic acid.

Lysozyme is a small 14 kDa protein found in tears. It contains 4 disulfide bonds and its secondary structure is both helical and sheet.

It hydrolyzes the bond between NAG subunits in bacterial cell walls and therefore serves as a defence mechanism.

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