A linear double-stranded DNA is $12$ base pairs long, with one strand $5^{'}$ -GCGAATTCGCGC- $3^{'}$ . Count each phosphodiester bond in both strands (A-T = 2 and G-C = 3 hydrogen bonds). The sum of the number of hydrogen bonds and the number of phosphodiester bonds is

Answer: C

GC pairs: 8, AT pairs: 4, so hydrogen bonds =

8 \times 3 + 4 \times 2 = 32

. Each strand of 12 nucleotides has 11 phosphodiester bonds, so 22 in all. Sum =

32 + 22 = 54