The sample of a virus was tested and it was found to contain 20% adenine, 20% thymine, 20 % guanine…………

Question 27:The sample of a virus was tested and it was found to contain 20% adenine, 20% thymine, 20 % guanine and the rest cytosine. Is the genetic material
of this virus (a) DNA- double helix (b) DNA-single helix (c) RNA? What do you infer from this data? How can Chargaff’s rule be used to infer that the genetic material of an organism is double- helix or single- helix?

The correct answer is – The genetic material of the virus cannot be DNA double-helix or RNA because the amounts of adenine, thymine, and guanine are equal, which violates Chargaff’s rule. In DNA, the amount of adenine always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. This suggests that the genetic material of this virus is DNA single-helix. In DNA single-helix, the amount of adenine and thymine does not necessarily have to be equal to the amount of guanine and cytosine. Chargaff’s rule can be used to infer that the genetic material of an organism is double-helix. In a double-helix DNA molecule, the amount of adenine always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. This is because adenine and thymine form two hydrogen bonds between them, while guanine and cytosine form three hydrogen bonds. This complementary base pairing allows the two strands of DNA to form a stable double helix.