Match List-I (Name of the Base) with List-II (Structure)
|
List-I Name of the Base |
List-II Structure |
|
(A) Adenine (A) |
(I) |
|
(B) Cytosine (C) |
(II) |
|
(C) Thymine (T) |
(III) |
|
(D) Guanine (G) |
(IV) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A)-(II), (B)-(IV), (C)-(I), (D)-(III)
The nitrogen bases of nucleic acids are of two kinds. Purines (adenine and guanine) have two fused rings, a six-membered and a five-membered one. Pyrimidines (cytosine, thymine and uracil) have a single six-membered ring. Within each kind, the groups on the ring (\( \ce{NH2} \), C=O, \( \ce{CH3} \)) tell the bases apart.
(A) Adenine (A) — This matches structure (II). A purine (two rings) with an \( \ce{NH2} \) group and no C=O group.
(B) Cytosine (C) — This matches structure (IV). A pyrimidine (one ring) with one \( \ce{NH2} \) group and one C=O group.
(C) Thymine (T) — This matches structure (I). A pyrimidine with two C=O groups and a \( \ce{CH3} \) group (5-methyluracil); it occurs in DNA, where RNA has uracil.
(D) Guanine (G) — This matches structure (III). A purine with both a C=O group and an \( \ce{NH2} \) group.
Shortcut: Structure (II) is the only two-ring base without a C=O group, so (A)-(II); only Option (3) has this pair.