Question

What is the complete base composition of a double-stranded eukaryotic DNA that contains \(22 \%\) guanine?

Short answer

Guanine: 22%, Cytosine: 22%, Adenine: 28%, Thymine: 28%

Step-by-step solution

Understand the Given Data

It is given that guanine (G) makes up 22% of the double-stranded DNA. Remember that in double-stranded DNA, guanine pairs with cytosine (C) and adenine (A) pairs with thymine (T).

Determine the Percentage of Cytosine

Since guanine (G) pairs with cytosine (C), and they are present in equal amounts, the percentage of cytosine (C) in the DNA is also 22%.

Calculate the Combined Percentage of G and C

Add the percentages of guanine (G) and cytosine (C) together: \[ 22\text{\text{%}} + 22\text{\text{%}} = 44\text{\text{%}} \]

Determine the Remaining Percentage

Subtract the combined percentage of G and C from the total 100% to find the combined percentage of adenine (A) and thymine (T): \[ 100\text{\text{%}} - 44\text{\text{%}} = 56\text{\text{%}} \]

Determine the Percentages of Adenine and Thymine

Since adenine (A) pairs with thymine (T) and they are present in equal amounts, divide this remaining percentage by 2 to find the percentage of each: \[ \frac{56\text{\text{%}}}{2} = 28\text{\text{%}} \]

Summarize the Base Composition

The base composition of the double-stranded eukaryotic DNA is: - Guanine (G): 22% - Cytosine (C): 22% - Adenine (A): 28% - Thymine (T): 28%

Key concepts

guanine-cytosine pairing

In the DNA of all living things, guanine (G) always pairs with cytosine (C). This is known as complementary base pairing. Guanine and cytosine have three hydrogen bonds between them, making their bond strong.
Because the DNA has two strands running in opposite directions, when there is a guanine on one strand, there is always a cytosine on the opposite strand. This 1:1 ratio means that the percentage of guanine must equal the percentage of cytosine in any given DNA sequence.
In a eukaryotic cell, the double-stranded DNA follows this rule strictly. If you find that guanine makes up 22% of the DNA, then cytosine must make up another 22%. This is because the strands are complementary and pair perfectly.
The total percentage of G and C together determines a portion of the DNA’s total base composition. One can find the other half of the composition by subtracting this combined percentage from the total (100%).

adenine-thymine pairing

Just as guanine pairs with cytosine, adenine (A) pairs with thymine (T). Adenine and thymine have two hydrogen bonds between them, which is slightly weaker compared to the three hydrogen bonds in a guanine-cytosine pair.
In eukaryotic DNA, the amount of adenine is always equal to the amount of thymine because of their complementary pairing. If we know the percentage of A and T together, we can easily split it to find the proportion of each.
For example, if the combined percentage of adenine and thymine is 56%, this means that half of this percentage is adenine and the other half is thymine. Therefore, each will make up 28% of the DNA.
This equal and precise pairing ensures the double-stranded DNA maintains stability and accurate genetic information encoding.

eukaryotic DNA

Eukaryotic DNA is the genetic material housed within the nucleus of eukaryotic cells, such as plants, animals, and fungi. Unlike prokaryotic DNA, which is typically circular and not enclosed in a nucleus, eukaryotic DNA is linear and organized into chromosomes.
Each chromosome consists of DNA tightly coiled around proteins called histones. This structure allows a large amount of DNA to fit within the nucleus and plays a critical role in regulating gene expression.
Understanding the base composition is essential in eukaryotic DNA studies as it helps decode the genetic blueprint of an organism. For instance, knowing that the DNA contains 22% guanine allows us to compute that the total content of guanine and cytosine together is 44%, and thus, adenine and thymine together must account for the remaining 56%.
The precise pairing of bases, such as guanine with cytosine and adenine with thymine, ensures that DNA replication is accurate and faithful across generations of cells.