A double-stranded DNA of 1000 base pairs contains 30% adenine (percentages are of all 2000 bases). Count two hydrogen bonds per A-T pair and three per G-C pair. The total number of hydrogen bonds is

A2000
B2400
C2200
D2600

Answer: B

A = 30% of 2000 = 600, so T = 600 and A-T pairs = 600. G = C = (2000 - 1200)/2 = 400, giving 400 G-C pairs. H bonds = 600 x 2 + 400 x 3 = 1200 + 1200 = 2400.

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