A dipeptide, “x”, on complete hydrolysis gives “y” and “z”; “y” on treatment with aqueous HNO2, produces lactic acid. On

Question

A dipeptide, “x”, on complete hydrolysis gives “y” and “z”; “y” on treatment with aqueous $\text{HNO}_2$ , produces lactic acid. On the other hand, “z” on heating gives the following cyclic molecule.

Six-membered cyclic diketopiperazine-like ring with two carbonyl groups opposite each other and two NH groups, containing two CH2 units in the ring.

Based on the information given, the dipeptide X is:

Accepted Answer

Given: A dipeptide x on complete hydrolysis gives amino acids y and z.

Find: The identity of the dipeptide x.

From the solution:

y gives lactic acid on treatment with aqueous $\text{HNO}_2$ , so y is identified as alanine.
z on heating gives the shown cyclic molecule, which is taken as the cyclic product characteristic of glycine.
Therefore, the dipeptide obtained from alanine and glycine is alanine-glycine.

Hence, the correct option is B.

Given: Complete hydrolysis of dipeptide x gives y and z.

Find: Which option matches x.

The provided working states that treatment of y with aqueous $\text{HNO}_2$ producing lactic acid suggests alanine.

It further states that the cyclic molecule formed by heating z corresponds to a condensation product characteristic of glycine.

So the hydrolysis products are:

y = alanine
z = glycine

Therefore, the dipeptide x is alanine-glycine.

The correct option is B.

Note: The second provided approach contains internally inconsistent chemistry, but the first approach and the declared correct option both support alanine-glycine.

Answer

Step-by-step solution

Common mistakes

Practice more Proteins (Amino Acids, Structure, Denaturation) questions

Related questions