Question

A double helical DNA molecule is composed of 32 mol% of adenosine. The mol% of cytosine in this DNA molecule is ______.

Hint:

In double-stranded DNA: A pairs with T, and G pairs with C. So, A = T and G = C; total must always be 100%.

Answer 1

Correct Answer: 18

Step 1: Apply Chargaff’s rule.
In double-stranded DNA: \[ \text{A} = \text{T}, \quad \text{G} = \text{C}, \quad \text{and} \quad (\text{A} + \text{T}) + (\text{G} + \text{C}) = 100% \] Step 2: Given.
A = 32 mol% ⇒ T = 32 mol%. \[ \text{A} + \text{T} = 64% \] Step 3: Find (G + C).
\[ 100 - 64 = 36% \] Since G = C, \[ \text{C} = 18%, \quad \text{G} = 18% \] Step 4: Conclusion.
\[ \boxed{\text{Cytosine (C)} = 18~\text{mol%}} \]