If a DNA double helix were composed of 10% thymine nucleotides, what would be the percentage of guanine nucleotides?

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BlackTom AI · Accepted Answer

Consider base-pairing rules in DNA: adenine pairs with thymine (A=T) and guanine pairs with cytosine (G=C). If the DNA double helix has 10% thymine, it must also have 10% adenine, leaving 80% of the nucleotides to be distributed between guanine and cytosine. Since G and C pair with each other and are present in equal amounts, each must constitute half of the remaining 80%. Half of 80% is 40%.

Option 10: This would imply A and T together are only 20%, which contradicts the given 10% T and the equal A. So this underestimates the remaining G+C portion.
Option 20: This would leave 60% for G and C combined, but G and C must be equal, so each would be 30%, not 20%.
Option 40: Correct. With A=10% and T=10%, the remaining 80% is split equally between G and C, giving G=40% and C=40%.
Option 80: This would require G or C to be 80%, which would exceed the total remaining after accounting for A and T and violate the 1:1 pairing of G with C.
Option Zero. Guanine is not present in DNA.: In reality, guanine is one of the four canonical nucleotides in DNA, so this statement is false.

2025 T3 DP DPST1051 BLSC1342 Molecules, Cells and Genes

If a DNA double helix were composed of 10% thymine nucleotides, what would be the percentage of guanine nucleotides?

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