Purines, Pyrimidines and Nucleic Acid Metabolism
While studying the structure of a small gene that was recently sequenced during the Human Genome Project, an investigator notices that one strand of the DNA molecule contains 20 As, 25 Gs, 30 Cs, and 22 Ts. How many of each base is found in the complete double-stranded molecule?
|A||A = 42, G = 55, C = 55, T = 42.|
|B||A = 44, G = 60, C = 50, T = 40.|
|C||A = 45, G = 45, C = 52, T = 52.|
|D||A = 50, G = 47, C = 50, T = 47.|
a. The two DNA strands are complementary to each other, with A base-paired with T, and G base-paired with C. So, for example, the 20 As on the first strand would be paired with 20 Ts on the second strand, the 25 Gs on the first strand would be paired with 25 Cs on the second strand, and so forth.
b. When these are all added together, the correct numbers of each base are indicated in choice E. Notice that, in the correct answer, A = T and G = C.