Question

In the DNA molecule

• A. the proportion of adenine in relation to thymine varies with the organism
• B. there are two strands which run antiparallel- one in 5' >> 3' direction and other in 3' '> 5'
• C. the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
• D. there are two strands which run parallel in the 5' '> 2' direction.

Answer 1

Answer: (B)

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.