AP BIOLOGY

THE MOLECULAR BASIS OF INHERITANCE

DNA MAKES RNA MAKES PROTEIN

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
If Chargaff found that a sample of DNA has 20% ADENINE, how much GUANINE would he have determined to be there?
A
30%
B
20%
C
80%
D
60%
Explanation: 

Detailed explanation-1: -Since adenine is 20%, then thymine is 20% as well. The total of both is 40%. From 100 remains 60% which is divided equally between guanine and cytosine, so each is 30%.

Detailed explanation-2: -Since cytosine and guanine are always present in equal numbers, the percentage of guanine molecule is 30%.

Detailed explanation-3: -The percentage of guanine is 20%.

Detailed explanation-4: -Hence, the sum of the purine residues equals the sum of the pyrimidine residues; i.e. A + G = T + C. Here, [A] = 30%, therefore, % of [T] is also 30%. Thus, [G]+[C] = 100-60 = 40%.

Detailed explanation-5: -It means the amount of guanine will be equal to cytosine and the amount of adenine will be equal to thymine. In the given problem, adenine is 20%. Hence, thymine will be 20%. So the percentage of cytosine and guanine will be 30% each.

There is 1 question to complete.