Question

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

Short answer

22% G, 22% C, 28% A, 28% T

Step-by-step solution

- Understand DNA Base Pairing

In a double-stranded DNA molecule, the bases pair as follows: adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). Thus, the percentage of A equals the percentage of T, and the percentage of G equals the percentage of C.

- Identify Known Percentages

Given that the DNA contains 22% guanine (G), it also contains 22% cytosine (C) because G pairs with C.

- Calculate Remaining Percentages

Since G and C together make up 44% of the DNA (22% G + 22% C), the remaining 56% is divided equally between adenine (A) and thymine (T), as A pairs with T. Therefore, A constitutes 28% and T also constitutes 28%.

- Summarize the Composition

The complete base composition of the DNA is 22% G, 22% C, 28% A, and 28% T.

Key concepts

double-stranded DNA

Double-stranded DNA is a molecule composed of two strands that wind around each other to form a double helix. Each strand is made up of nucleotides, which are the basic building blocks of DNA.
Nucleotides consist of three components: a phosphate group, a sugar molecule (deoxyribose), and one of four nitrogenous bases.
The nitrogenous bases include adenine (A), thymine (T), guanine (G), and cytosine (C). The strands are held together by hydrogen bonds between complementary bases.
This structure is essential for the storage and transmission of genetic information in eukaryotic cells.

base pairing rules

The base pairing rules, also known as Chargaff's rules, are pivotal in understanding DNA structure. According to these rules:

• Adenine (A) always pairs with thymine (T)
• Guanine (G) always pairs with cytosine (C)

Each pairing is due to the specific number of hydrogen bonds they can form. Adenine and thymine form two hydrogen bonds, while guanine and cytosine form three.
This consistency is critical for DNA replication and transcription.

nucleotide percentage calculation

To calculate the nucleotide percentages in a double-stranded DNA, you can use the base pairing rules:

• If a DNA sample has 22% guanine (G), it must have 22% cytosine (C) because of the G-C pairing.
• The combined percentage of G and C is 44% (22% + 22%).
• The remaining 56% of the DNA must be adenine (A) and thymine (T). Since A pairs with T equally, 56% is divided by 2, giving 28% A and 28% T.

Thus, the complete DNA composition would be 22% G, 22% C, 28% A, and 28% T.

eukaryotic DNA

Eukaryotic DNA refers to the DNA found within the nucleus of eukaryotic cells. Unlike prokaryotes, which have a single circular DNA molecule, eukaryotic cells contain multiple linear chromosomes.
Each chromosome is made of DNA tightly coiled around histone proteins to form a structure called chromatin. This organization allows the extensive DNA to fit within the nucleus and is essential for gene regulation.
Eukaryotic DNA undergoes more complex processes for replication and transcription, and it contains non-coding regions known as introns, which are not present in prokaryotic DNA.
This complex structure and regulation make eukaryotic DNA unique and vital for the sophisticated functioning of eukaryotic organisms.