Question

If 30% of the bases in a particular DNA molecule are guanine(G), what percentage of the bases would be thymine(T)? Explain your reasoning.​

Answer 1

Since 30% of the bases are guanine, we know that 30% must also be cytosine (because it pairs with guanine in DNA).

Knowing this, we have figured out 60% out of 100%, leaving us with 40%.

Thymine pairs with Adenine, so Thymine and Adenine each make up 20% of the remaining 40% of the DNA in this example.

In total:

Guanine: 30%

Thymine: 20%

Cytosine: 30%

Adenine: 20%

Answer 2

Percentage of thymine will be 20%

• Deoxyribonucleic acid (DNA) is a double stranded molecule and one of the two types of nucleic acids. It is made up of nucleotides subunit namely: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T).

• Adenine (A) pairs with Thymine (T) while Guanine (G) pairs with Cytosine (C) in the DNA molecule. According to Chargaff in his rule, the amount of all four bases equals to 1 i.e.

A + G + C + T = 100% or 1

• In a DNA molecule, Adenine = Thymine and Guanine = Cytosine. This means that the amount of adenine and thymine is equal and the same goes for cytosine and guanine.

• According to this question, If 30% of the bases in a particular DNA molecule are guanine(G). This means that the percentage of its pair (Cytosine) will also be 30%.

That is;

A = T + G = C = 100%

A + T + (30 + 30) = 100

A + T + 60 = 100

A + T = 40

T = 40/2 = 20%

Hence, the percentage of thymine and adenine will be 20% each.