A sample of double-stranded DNA is found to contain 20% cytosine. Determine the percentage of the three other DNA nucleotides in the sample.

Key Concepts

Base Pairing Rules

In DNA, the base pairing rules dictate that adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This means that the amount of adenine will equal the amount of thymine, and the amount of cytosine will equal the amount of guanine in a double-stranded DNA molecule. Understanding these rules is essential for calculating the percentages of the nucleotides based on the given information.

Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases in DNA. Since the sample contains 20% cytosine, it must also contain 20% guanine due to their complementary nature. This relationship allows us to deduce the percentages of the other nucleotides by knowing the total percentage must equal 100%.

Percentage Composition of DNA

The percentage composition of DNA nucleotides is calculated based on the total amount of each base present. Given that the total must equal 100%, if cytosine and guanine each account for 20%, the remaining percentage (60%) must be divided equally between adenine and thymine, leading to 30% for each. This concept is crucial for solving the problem presented.