July 31, 2012

Concerning physiological defence mechanisms

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.

See more of the cell wall on Wikipedia or Todar's Online Textbook of Bacteriology.

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