Question

1. What fraction of the nucleotides in a double-stranded DNA molecule are adenine and guanine (% A and % G added together)?

1. 25 %
2. 50 %
3. 75 %
4. 100%
5. It depends on the DNA sequence

Answer 1

Answer :- B ( 50 %)

Explanation :-

The complementary base pairing of DNA helix proves chargaff's rule. The contant of adenine equals to thymine and guanine equals to that of cytosine. According to chargaff's rule, molar equivalence between the purines ( A and G) and pyrimidines ( T and C ) in DNA structure.

Example :-

In a DNA total base pair are 30, and in the DNA sequence adenine are 16 and cytosine are 14, so find out percentage of purine ?

Answer :-

Adenine are 16 so number of thymine are also 16

Cytosine are 14 so number of guanine are also 14

Then,

purine ( A + G) = pyrimidines ( C + T)

16 + 14 = 14 + 16

30 = 30

50 % = 50 %

So the percentage of purine is 50 %