[Campbell Biology P.369] A double-stranded DNA molecule is analyzed, and it is found that 22... | Practice Question

A double-stranded DNA molecule is analyzed, and it is found that 22% of its nitrogenous bases are Cytosine C . Based on Chargaff's rules as described in the text, what percentage of the bases in this DNA molecule would be Adenine A ?

  • A: 22%
  • B: 28%
  • C: 44%
  • D: 56%

Explanation

Chargaff's rules state that in DNA, the amount of adenine equals the amount of thymine A=T , and the amount of guanine equals the amount of cytosine G=C . If C = 22%, then G must also be 22%. The total percentage of G and C is 22% + 22% = 44%. The remaining percentage must be for A and T: 100% - 44% = 56%. Since A = T, Adenine would be 56% / 2 = 28%.