Question

Study the following list: I. Lys, II. Gln, III. Ser, IV. Cys, V. Tyr, VI. Asn. X is the set of amino acids containing -OH group and Y is the set of amino acids containing -CONH$_2$ group. What are X and Y respectively?

• A. III, IV; II, V
• B. III, IV; I, II
• C. III, V; I, VI
• D. III, V; II, VI

Hint:

Serine/Tyrosine contain -OH; Glutamine/Asparagine contain -CONH$_2$.

Answer 1

The Correct Option is D

Step 1: We need two groups of amino acids.
Set X must have an alcohol type -OH group on the side chain. Set Y must have an amide type -CONH$_2$ group on the side chain. Let us scan the list.

Step 2: Find the -OH side chains.
Serine (III) has a -CH$_2$OH side chain. Tyrosine (V) has a phenol -OH on its ring. Both carry the -OH group, so X = III, V.

Step 3: Note what cysteine has.
Cysteine (IV) carries an -SH (thiol) group, not -OH, so it does not belong in X. This rules out the options that put IV in X.

Step 4: Find the -CONH$_2$ side chains.
Glutamine (II) and asparagine (VI) both have an amide -CONH$_2$ group in their side chains. So Y = II, VI.

Step 5: Note what lysine has.
Lysine (I) has a plain amine -NH$_2$ group, not an amide, so it is not in Y.

Step 6: Conclusion.
So the answer is X = III, V and Y = II, VI. \[ \boxed{\text{III, V; II, VI}} \]