Question

the analysis of a dna molecule reveals that 30% of its nucleotides are adenine. what percentage of the same dna molecule would be expected to be guanine nucleotides?
○ 20%
○ 30%
○ 40%
○ 60%

Explanation:

Step1: Apply Chargaff's base pairing rule

In DNA, adenine (A) pairs with thymine (T), so %A = %T. Given %A = 30%, so %T = 30%.

Step2: Calculate total of A+T

$\%A + \%T = 30\% + 30\% = 60\%$

Step3: Calculate total of G+C

Total nucleotides = 100%, so $\%G + \%C = 100\% - 60\% = 40\%$

Step4: Find %G (guanine)

Guanine (G) pairs with cytosine (C), so %G = %C. $\%G = \frac{40\%}{2} = 20\%$

Answer:

20%