Question

A DNA molecule consists of 1300 hydrogen bonds between base pairs
with 20% adenine. Total number of C - N rings present in the molecule is?

Please answer this question with EXPLAINATION.. ​

Answer 1

Answer:

1500

Explanation:

Since Adenine pairs with Thymine and Guanine pairs with cytosine. Hence the quantity of Thymine, Cytosine and Guanine is 20%, 30% and 30% respectively.

Therefore, in a given DNA molecule, the ratio of amount of Adenine to Cytosine is 2:3.

Since, Adenine pairs with Thymine (A=T) with two hydrogen bonds. Guanine pairs with Cytosine (G≡C) with three hydrogen bonds. Hence the ratio of their bonds is 2:3.

Therefore, ratio of total number of bonds formed by Adenine to the total number of bonds formed by Cytosine in a given DNA molecule = ratio of quantity × ratio of bonds = (2/3) x (2/3) =4/9.

Therefore, the number of bonds formed by Adenine = 4 x [ 1300/(4+9) ] = 400.

Therefore, the number of Adenine and Thymine = 400/number of bonds between Adenine and Thymine = 400/2 = 200.

Similarly, the number of bonds formed by Cytosine = 9 x [ 1300/(4+9) ] = 900.

Therefore, the number of Cytosine and Guanine = 900/number of bonds between Guanine and Cytosine = 900/3 = 300.

Since, Purine (Adenine and Guanine) contains double carbon-nitrogen (c-n) ring.

Therefore, the total number of c-n ring in purine = (A+G) x 2 = (200+300) x 2 = 1000.

Similarly, Pyrimidine (Thymine and cytosine) contains single carbon-nitrogen (c-n) ring.

Therefore, the total number of c-n ring in pyrimidine = (T+C) x 1 = (200+300) x 1 = 500.

Therefore, the total number of c-n rings in a given DNA molecule = total number of c-n rings in purines + total number of c-n rings in pyrimidine = 1000 + 500 = 1500.