Question

If the DNA analyses of the gene shows 20% Adenine bases, what would be the percentage of Thymine, Cytosine, Guanine and Uracil?

Answer 1

Hint: Erwin Chargaff proposed two rules which are termed as Chargaff’s rules. This rule played an important role in the discovery of the double helix structure of DNA.

Complete answer:
DNA is composed of nucleotides, each of which contains a nitrogen-containing base, a five-carbon sugar (deoxyribose), and a phosphate group. There are four types of nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T). Adenine and guanine are purine bases, and cytosine and thymine are pyrimidine bases. Instead of thymine there is uracil in RNA.

Chargaff's rule:
In any double stranded DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units.
The composition of DNA varies from one species to another.

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%. Uracil is not found in DNA but it will have the same percentage as thymine, i.e the RNA will have 30% uracil.
1)Adenine= 20%
2)Thymine=20%
3)Guanine=30%
4)Cytosine=30%
5)Uracil=30%

Note: In double stranded DNA
1)The molar ratio of A to T equals to 1. Similarly the molar ratio of G to C equals to 1
2)The sum of purines (A and G) equals that of the pyrimidines (C and T)
3)The percentage of C+G does not necessarily equal the percentage of A+T.