b If the DNA chromosomes of humans contain 20% cytosine, what is the percent of guanine, adenine, and thymine?

Verified step by step guidance

1. Understand that DNA is composed of four nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).
2. Recall Chargaff's rules, which state that in DNA, the amount of cytosine (C) is equal to the amount of guanine (G), and the amount of adenine (A) is equal to the amount of thymine (T).
3. Given that cytosine (C) is 20%, according to Chargaff's rules, guanine (G) must also be 20%.
4. Since the total percentage of all nucleotides must equal 100%, calculate the combined percentage of adenine (A) and thymine (T) by subtracting the percentage of cytosine (C) and guanine (G) from 100%.
5. Divide the remaining percentage equally between adenine (A) and thymine (T), as they are present in equal amounts according to Chargaff's rules.

Key Concepts

Chargaff's Rules

Chargaff's Rules state that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of cytosine (C) is equal to guanine (G). This means that if you know the percentage of one base, you can determine the percentage of its complementary base. For example, if cytosine is 20%, then guanine must also be 20%.

Base Pairing in DNA

Base pairing in DNA refers to the specific pairing of nitrogenous bases: adenine pairs with thymine, and cytosine pairs with guanine. This complementary base pairing is crucial for the structure of the DNA double helix and ensures accurate replication and transcription of genetic information. Understanding this concept is essential for calculating the percentages of the other bases when one is known.

Percentage Composition of DNA Bases

The percentage composition of DNA bases refers to the relative amounts of adenine, thymine, cytosine, and guanine in a DNA molecule. Since the total percentage of all four bases must equal 100%, knowing the percentage of one base allows for the calculation of the others. In this case, if cytosine is 20%, then guanine is also 20%, leaving 60% to be divided equally between adenine and thymine.