Class 12th Biology 2015 Set3 Delhi Board Paper Solution
Question 15
(a) A DNA segment has a total of 2,000 nucleotides, out of which 520 are adenine containing nucleotides. How many purine bases this DNA segment possesses ?
(b) Draw a diagrammatic sketch of a portion of DNA segment to support your answer.
Answer
(a)
Adenosine (A) and guanine (G) are purines, while thymine (T) and cytosine (C) are pyrimidines. According to the Chargaff's rule, purine will pair with pyrimidines; therefore, 'A pairs with T' and 'C pairs with G'.
We have 520 adenine bases;therefore, there should be 520 thymine bases.
A + T = 520 + 520 = 1040
Total number of nucleotides are 2000.
G + C = 2000 − 1040 = 960
G = 960/2 = 480
Therefore, total number of purine bases are 1000 (A + G = 520 + 480).
(b) Diagram Showing DNA Segment
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