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' $\to$ 3' direction and other in 3' $\to$ 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' $\to$ 3' direction

Answer 1

The correct option is B there are two strands which run antiparallel one in 5' $\to$ 3' direction and other in 3' $\to$ 5'

The double stranded DNA molecule has 2 strands. One runs in the 5' → 3' direction and the other strand runs in the 3' → 5' direction. The pyrimidine A always bonds with purine T in the complementary strand. And the pyrimidine G always binds with the purine C. Therefore, the total number of purines is always equal to the total number of pyrimidines in the DNA molecule. Thus, the proportion of adenine to thymine is always the same in all organisms.