Question

A double-stranded DNA molecule of 175 base pairs long had (A+T/(G+C) = 0.75. How many adenine nucleotides are there in this DNA? 75 37.5 150

Answer 1

A+T/G+C= 0.75

A+T= 0.75 (G+C)

G+C= (A+T)/0.75

total number of basepairs= 175

there are two bases in a basepair, total number of bases= 2$\times$175

A+T+G+C= 2$\times$175

A+T+ (A+T)/0.75=2$\times$175

(0.75 (A+T)+ (A+T))/0.75= 2$\times$175

0.75 (A+T)+ (A+T)= 2$\times$175$\times$0.75

1.75 (A+T)=2$\times$175$\times$0.75

A+T= 2$\times$175$\times$​​​​​​​0.75/1.75

= 150

A basepairs with T so number of A`s = number of T`s

so number of A`s= 150/2=75

so the answer is a) 75