Question

A viral genome is studied. It is composed of 33% Adenine, 28% Thymine, 22% Cytosine and 17% Guanine. Predict whether this genome is single or double stranded and whether it is DNA or RNA based.

A) The genome is DNA based and single stranded.

B) The genome is DNA based and double stranded.

C) The genome is RNA based and single stranded.

D) The genome is RNA based and double stranded.

Answer 1

B

Explanation: RNA contains the nucleotide “Uracil” therefore this could not be RNA and the percentages closely match up therefore we can assume that the DNA is double stranded I.e. Double helix

Answer 2

Answer:

A) The genome is DNA based and single stranded.

Explanation:

The reason why it is DNA based is because DNA contains thymine base (T). It is not RNA based because RNA contains uracil base (U) instead of thymine and in the given question there is not uracil mentioned.

It is single stranded because according to Chargaff's rule a double stranded nucleic acid must have the ratio of purine bases to pyrimidine ratio as 1:1.

Adenine (A) & Guanine (G) are purine bases while Thymine (T) & Cytosine (C) are pyrimidine bases so according to Chargaff's rule AG/CT = ~ 1. It means [A+G] = [C+T]

Also, A makes interaction with T while C makes interaction G. It means,

[A] = [T]

[C] = [G]

By this we can easily infer that a double stranded DNA will have as much A as much it has T & same goes with C & G.

But, in the given question, A = 33% while Thymine = 28% which are not equal so this means that this molecule is single stranded.