In the DNA molecule:
Correct answer: B. There are two strands which run antiparallel; one in the 5' ➡ 3' direction and the other in 3' ➡ 5' direction
- A. The proportion of adenine in relation to thymine varies with the organism
- B. There are two strands which run antiparallel; one in the 5' ➡ 3' direction and the other in 3' ➡ 5' direction
- 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' ➡ 3' direction
Explanation
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 directions. One chain has the polarity 5' ➡ 3', whereas the 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 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 amounts (A + G = T + C), but A + T is not necessarily equal to G+C.
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