JEE Main 2025 Apr 4 Shift 1, Chemistry Q25: Nucleic Acids

JEE Main2025Apr 4, Shift 1Chemistry

The total number of hydrogen bonds of a DNA-double Helix strand whose one strand has the following sequence of bases is ______.

5' $-$ G $-$ G $-$ C $-$ A $-$ A $-$ A $-$ T $-$ C $-$ G $-$ G $-$ C $-$ T $-$ A $-$ 3'

Your answer

Solution

In double-stranded DNA, the base pairs are A=T (joined by 2 H-bonds) and G $\equiv$ C (joined by 3 H-bonds).

Count the bases in the given strand: G, G, C, A, A, A, T, C, G, G, C, T, A.

G $+$ C $= 4 + 3 = 7$ bases (each contributes 3 H-bonds to its partner) $\Rightarrow 7 \times 3 = 21$ H-bonds.

A $+$ T $= 4 + 2 = 6$ bases (each contributes 2 H-bonds) $\Rightarrow 6 \times 2 = 12$ H-bonds.

Total H-bonds $= 21 + 12 =$ 33.

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