Question

If the G-C content of a DNA molecule is 60 percent, what are the molar percentages of the four bases (G,C,T,A)?

a) 30%, 30%, 20%, 20%
b) 30%, 30%, 25%, 15%
c) 60%, 40%, 0%, 0%
d) 20%, 20%, 30%, 30%

Answer 1

The G-C content of 60 percent in a DNA molecule means that guanine and cytosine each make up 30 percent, and the remaining 40 percent is equally divided between adenine and thymine (20 percent each).

Step-by-step explanation:

If the G-C content of a DNA molecule is 60 percent, then according to Chargaff's rules, the amounts of guanine (G) and cytosine (C) are equal, each accounting for 30 percent of the total bases in the DNA. Because DNA is a double helix where adenine (A) always pairs with thymine (T), the remaining 40 percent of the DNA must be composed equally of A and T. Thus, each of these bases would account for 20 percent of the total bases. Therefore, the correct molar percentages of the four bases G, C, T, and A would be 30%, 30%, 20%, and 20% respectively, which corresponds to option (a).