JEE Main 2022 · 30 June · morning · Single correct · +4 / −1
The sugar produced after complete hydrolysis of DNA is
- (a) a pentose sugar.
- (b) a hexose sugar.
- (c) a polysaccharide.
- (d) a disaccharide.
Answer and solution
Answer (a) a pentose sugar.
Solution
Chemistry ma’am · 4 steps
Break DNA into its smallest pieces and see which sugar is left: it has five carbons, not six.
- Parts of DNA. DNA is a long chain of nucleotides. Each nucleotide has three parts: a phosphate group, a nitrogenous base and a sugar.
- Complete hydrolysis. Complete hydrolysis breaks every link in the chain. What comes out is phosphoric acid, the four bases (A, G, C, T) and one sugar, 2-deoxy-D-ribose.
- Count the carbons. 2-Deoxyribose, C₅H₁₀O₄, has five carbon atoms, so it is a pentose. It is ribose with the OH group on C-2 replaced by H. That is where the "deoxy" in DNA comes from.
- So. The sugar from complete hydrolysis of DNA is a single five-carbon monosaccharide, a pentose. The answer is (a).
The idea to keep. Both nucleic acids carry pentoses: RNA has ribose and DNA has 2-deoxyribose. Hydrolysis always ends at single monosaccharides, never at di- or polysaccharides.
Answer from the NTA final answer key. Solution by PrepWiser.