Question

If Adenine makes $30 \%$ of the DNA molecule, what will be the percentage of Thymine, Guanine and Cytosine in it?

• A. $T : 20 ; G : 30 ; C : 20$
• B. $T : 20 ; G : 20 ; C : 30$
• C. $T : 30 ; G : 20 ; C : 20$
• D. $T : 20 ; G : 25 ; C : 25$

Answer 1

The Correct Option is C

To determine the percentage of Thymine (T), Guanine (G), and Cytosine (C) in a DNA molecule where Adenine (A) makes up 30%, we need to understand the base pairing rules of DNA. 

1. In DNA, Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). This is known as Chargaff's Rule.
2. This means the amount of Adenine (A) is equal to the amount of Thymine (T), and the amount of Guanine (G) is equal to the amount of Cytosine (C).
3. Given that Adenine (A) makes up \(30 \%\) of the DNA, the percentage of Thymine (T) must also be \(30 \%\).
4. Since the total percentage of all the bases must equal \(100 \%\), the remaining percentage for Guanine (G) and Cytosine (C) combined is \(100 \% - (30 \% + 30 \%) = 40 \%.\)
5. Assuming the DNA is double-stranded and the percentages of G and C are equal, the percentage for Guanine (G) is \(20 \%\), and for Cytosine (C) is also \(20 \%.\)

Therefore, the percentage composition of Thymine, Guanine, and Cytosine in the DNA is:

• Thymine (T): \(30 \%\)
• Guanine (G): \(20 \%\)
• Cytosine (C): \(20 \%\)

The correct answer is \(T : 30 ; G : 20 ; C : 20\).