Question

Thirty percent of the bases in a sample of DNA extracted from eukaryotic cells is adenine. What percentage of cytosine is present in this DNA?
A. 10%
B. 20%
C. 30%
D. 40%

Answer 1

Hint: Nucleobases, also referred to as nitrogenous bases or frequently just bases, are biological substances containing nitrogen that combine to produce nucleosides, which are the parts of nucleotides, all of which serve as the fundamental building blocks of nucleic acids.

Complete step by step solution:
Nitrogenous base: A nitrogen-containing molecule with base-like chemical characteristics. Adenine (A), guanine (G), thymine (T), and cytosine (C) are the nitrogenous bases found in DNA (C). With one exception, the nitrogenous bases found in RNA—adenine (A), guanine (G), uracil (U), and cytosine—are all the same (C). An organic molecule called a nitrogenous base functions as a base in chemical processes and contains the element nitrogen. The nitrogen atom's single electron pair is the source of the fundamental characteristic.
The two types of nitrogenous bases found in DNA are purines (Adenine (A) and Guanine (G)) and pyrimidines (Cytosine (C) and Thymine (T)). A glycosidic link connects these nitrogenous bases to the C1' of deoxyribose. A nucleoside is made up of deoxyribose and a nitrogenous base. DNA is composed of the four nitrogen bases adenine, guanine, cytosine, and thymine. Thymine is swapped out for the nucleotide uracil when the genetic code is copied to RNA, a related molecule that is used to make proteins. The bases of the genetic code are denoted by the letters A, G, C, T, and U.
According to Chargaff's rule, if adenine makes up 30% of DNA, then thymine will make up 30%. Cytosine and guanine make up the remaining 40% of DNA. Each makes up 20% of the bases since the ratio of cytosine to guanine must be equal.
So, the correct answer is option B, 20%.

Note:
Pyrimidines and purines are the two categories of nitrogenous bases found in DNA and RNA. One carbon-nitrogen ring with two nitrogen atoms makes up a pyrimidine. A pyrimidine and an imidazole ring are joined to form a purine. Purines include adenine and guanine.