If thymine makes up 21% of the DNA nucleotides in the genome of a plant species, what are the percentages of the other nucleotides in the genome?

Verified step by step guidance

1. span>Step 1: Understand Chargaff's rules, which 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).
2. span>Step 2: Given that thymine (T) makes up 21% of the DNA, according to Chargaff's rules, adenine (A) will also make up 21% of the DNA.
3. span>Step 3: Calculate the combined percentage of adenine (A) and thymine (T) in the DNA, which is 21% + 21% = 42%.
4. span>Step 4: Since the total percentage of all nucleotides must equal 100%, calculate the remaining percentage for cytosine (C) and guanine (G) by subtracting the combined percentage of adenine and thymine from 100%: 100% - 42% = 58%.
5. span>Step 5: Divide the remaining percentage equally between cytosine (C) and guanine (G), since they are present in equal amounts according to Chargaff's rules: 58% / 2 = 29% for each.

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 percentage of adenine in the DNA will be equal to the percentage of thymine. Therefore, if thymine constitutes 21% of the nucleotides, adenine will also make up 21%.

Chargaff's Rules

Chargaff's rules state that in any given DNA molecule, the amount of adenine equals thymine, and the amount of cytosine equals guanine. This principle is crucial for calculating the percentages of the other nucleotides when one nucleotide's percentage is known, as it establishes a predictable relationship between the bases.

Total Percentage of Nucleotides

The total percentage of all four nucleotides (adenine, thymine, cytosine, and guanine) in a DNA molecule must equal 100%. By knowing the percentages of adenine and thymine, one can deduce the percentages of cytosine and guanine by subtracting the known percentages from 100%, ensuring that the total adds up correctly.