Question

Which one of the following peptides lacks a chiral center at the first position, is devoid of a hydrogen in the backbone amide at the second position and the side-chain of the third residue has a pk, close to the physiological pH?
a. Gly-Pro-Tyr
b. Pro-Gly-Tyr
C. Pro-Gly-His
d. Gly-Pro-His
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Answer 1

Answer:

YOUR ANSWER IS (D)

Explanation:

first of all using the first statement we eliminate all others except (a) and (d) SINCE ONLY GLYCINE IS AMINO ACID WHICH HAS NO CHIRAL CARBON which has structure as in fig. AND SINCE PROLINE IS COMMON IN BOTH OPTION (a) and (d) so we need not to check it and the according to last statement the physiologucal ph is 7.4 so nearest to it is histidine with ph=6

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