Question

If a DNA molecule is found to be composed of 40% thymine, what percentage of guanine would be expected.

Answer 1

Answer:

10%

Explanation:

Chargaff postulated the complementary base pairing rule, where he stated that in the DNA molecule, Adenine (A) will always pair with Thymine (T) and Guanine (G) with Cytosine (C) i.e. A-T, G-C

Chargaff stated that the concentration of purines (Adenine and Guanine) is always equal to that of pyrimidines (Thymine and Cytosine) i.e. {A} + {G} = {C} + {T}

These equal concentration equals 100% in totality i.e. A+G+C+T= 100%

Thymine pairs with Adenine, if there is 40% of Thymine in the DNA molecule, it means there will be 40% of Adenine also. 40 + 40 = 80%. This leaves us with 100-80 = 20% for Guanine and Cytosine.

Since there will be an equal amount of Guanine and Cytosine too, Guanine will therefore, be 20/2 = 10%.

That is, 10% Guanine, 10% Cytosine.