JEE Main 2022 · 29 June · morning · Single correct · +4 / −1
Sugar moiety in DNA and RNA molecules respectively are
- (a) β-D-2-deoxyribose, β-D-deoxyribose.
- (b) β-D-2-deoxyribose, β-D-ribose
- (c) β-D-ribose, β-D-2-deoxyribose.
- (d) β-D-deoxyribose, β-D-2-deoxyribose.
Answer and solution
Answer (b) β-D-2-deoxyribose, β-D-ribose
Solution
Chemistry ma’am · 3 steps
DNA is literally deoxyribonucleic acid: its sugar has lost the OH at C2. RNA keeps it.
- The sugar in RNA. RNA is ribonucleic acid. Its sugar is β-D-ribose, a five-carbon furanose sugar with an -OH group on every ring carbon from C1 to C3 and a -CH₂OH at C4.
- The sugar in DNA. DNA is deoxyribonucleic acid. Its sugar is the same ring, but the -OH at C2 is replaced by -H. That is why it is called β-D-2-deoxyribose.
Nucleic acid Group at C2 Sugar DNA -H β-D-2-deoxyribose RNA -OH β-D-ribose - So. In the order DNA, then RNA, the sugars are β-D-2-deoxyribose and β-D-ribose, which is option (b).
The idea to keep. Both nucleic acids use a β-D pentose. The only difference is at C2: -OH in RNA's ribose, just -H in DNA's 2-deoxyribose. The 'deoxy' belongs only to DNA.
Answer from the NTA final answer key. Solution by PrepWiser.