(a) A DNA segment has a total of 1000 nucleotides, out of which 240 of them are adenine containing nucleotides. How many pyrimidine bases this DNA segment possesses?
(b) Draw a diagrammatic sketch of a portion of DNA segment to support your answer.

Explanation

Cytosine and thymine are priymidines ,According to Chargaff's rule of purine to pyrimidines is equal .
Number of adenine (A) will be equal to the number of thymine (T) A=T=240
`rArr A+T= 240 + 240 `
= 480 Number of cytocine ( c) will to equal to the number of guanine (G)
G=C
`rArr G+C `= total number of nucleotides - Nucleotids containing A and T nitrogenous base
`=1000 -(A+T) rArr 1000-480`
= 520
G+C = 520
`G= 520//2= 260 `
`G= 260 & C=2`
Number of Pyrimidines in the segment processes = C+T= 260 +240 = 500
(b) Diarammatic sketch of a portion of DNA segment .