Question

Denaturation of DNA after heating can be studied by comparing

• A. Number of nucleotides
• B. A : T ratio
• C. C : G ratio
• D. Sugar phosphate ratio

Answer 1

Answer: (A)

Number of nucleotides

Denaturation is disruption of the hydrogen bonds between bases pairs and disturbed base stacking which in turn causes unwinding of the double helix to form two single strands. As no covalent bonds in the DNA are broken during denaturation, sugar phosphate ratio cannot be used to detect it; option D is wrong. As there are two hydrogen bonds between adenine and thymine, DNA strands rich in A-T bases have low melting temperature as compared to G-C rich DNA segments. But their ratio is not a measure to detect denaturation; options B and C are wrong. Denaturation of a double-stranded DNA causes an increase in absorption, the hyperchromic effect, due to increased number of nucleotides caused by disturbed base pairing and base stacking. Thus, DNA denaturation can be detected by measuring the absorption of UV light.