List-II (I) (see structure) (II) (see structure) (III) (see structure) (IV) (see structure)
Choose the correct answer from the options given below :
Answer: A → III, B → IV, C → II, D → I
Solution
The nitrogenous bases fall into two structural classes. Adenine is a purine — a fused bicyclic ring system bearing an −NH2 group — distinguishing it from the pyrimidines. Cytosine, thymine and uracil are all single six-membered pyrimidine rings that differ in their substituents: cytosine carries one amino group and one carbonyl (4-amino, 2-oxo), thymine carries two carbonyls (2,4-dioxo) plus a 5-methyl group, and uracil carries the same two carbonyls without the methyl group.
Matching each base to its structure: Adenine is the bicyclic purine bearing −NH2; Cytosine is the pyrimidine with one amino and one carbonyl group; Thymine is the pyrimidine with two carbonyls and a methyl substituent; Uracil is the pyrimidine with two carbonyls and no methyl group.
JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Match the columns
