Question

(a) A DNA segment has a total of 1,500 nucleotides, out of which 410 are guanine containing nucleotides. How many pyrimidine bases this segment possesses?
(b) Draw a diagrammatic sketch of a portion of DNA segment to support your answer.

Answer 1

Adenine an Guanine are purines while cytosine and thymine are pyrimidines.

According to Chargaff's rule, the ratio of purines to pyrimidines is equal.

Thus, the number of cytosine (C) will be equal to the number of guanine (G).

As it is given that the number of guanine-containing nucleotides = 410

Thus, G = C = 410

Now, G + C = 410 + 410 = 820

The number of adenine (A) will be equal to the number of thymine (T).

Thus, A + T = Total number of nucleotides – Nucleotides containing G and C nitrogenous bases

= 1500 – 820 = 680

Therefore, A = 340 and T = 340

The number of adenine will be equal to number of thymine, which is 340.

Therefore, Number of pyrimidines that the segment possess = C + T

= 410 + 340 = 750