Question

If 24% of an organism's DNA is thymine, what percent is cytosine?

a. 24%
b. 26%
c. 48%
d. 52%

Answer 1

B. 26%

Step-by-step explanation:

According to the Chargaff rule, we know that the quantity of thymine and adenine, and the quantity of cytosine and guanine are exactly the same in the DNA.

We can conclude that if there is 24% of thymine, there is also 24% of Adenine. Because those bases pair with each other and there is going to be the same percentage of them both in the DNA.

The sum of the 4 bases is going to be 100% in the DNA

`A+T+C+G=100%`

Since 24% of the organism is thymine 24% is going to be adenine

`24+24+C+G=100`

To know how much is missing from the equation we would have to subtract the total 48%

`C+G=100-48\\C+G=52\\`

This means that the remaining 52% is composed by the cytosine-guanine pairs. Since the pairs are equal in quantity in the DNA, we have to divide this number by 2 to have the amount of each one

`C=(52)/(2) \\C=26`

The answer is: B.26% is going to be the percent of cytosine and also guanine in the DNA