Explanation

Refer to answer (A DNA molecule has two unbranched complementary strands which are spirally coiled. The two chains are antiparallel, i.e., they run parallel but in opposite direction. One chain has the polarity 5′ → 3′ whereas, other has 3′ → 5′. Both are held together by hydrogen bonds between their bases, i.e., A = T and G ≡ C and the amount of adenine is equal to thymine and guanine equals to cytosine. The base ratio A + T / G + C may vary from one species to another but is constant for a given species. The purine and pyrimidines are always in equal amount (A + G = T + C) but A + T is not necessarily equal to G + C).