Final answer:
Statement c is true: if the percentage of one base is known, the percentage of its corresponding base can be inferred due to the A-T and G-C pairing in DNA's complementary base pairing.
Step-by-step explanation:
Based on the Watson-Crick model of DNA structure, the correct statement among those provided is c. if the percentage of one nitrogenous base is known, the percentage of the other nitrogenous bases are known. This is because, in the double helix model of DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). Therefore, if the percentage of adenine is known, for example, the percentage of thymine will be the same, due to the complementary base pairing rule.
Contrary to the options presented:
- The two strands of DNA are anti-parallel, not parallel; the 3' end of one strand is opposite to the 5' end of the other.
- It is not accurate to say that the double helix contains 40% purines and 60% pyrimidines because there is always an equal proportion of purines (adenine and guanine) and pyrimidines (cytosine and thymine).
- For every adenine there is a corresponding thymine, not guanine, and vice versa for cytosine and guanine.