Which of the following statements about deamination is true?
A. Deamination of cytosine causes a transversion mutation.
B. Deamination of cytosine results in uracil.
C. Deamination of cytosine results in thymine.
D. Deamination of thymine results in uracil.
The Correct Answer and Explanation is:
The correct answer is B. Deamination of cytosine results in uracil.
Explanation
Deamination is a biochemical process that involves the removal of an amino group (–NH2) from an amino acid or nucleotide, converting it into a corresponding keto acid or in the case of nucleotides, a different base. In the context of nucleotides, deamination can significantly affect the integrity of DNA.
1. Deamination of Cytosine:
Cytosine (C) is a nitrogenous base found in DNA and RNA. When cytosine undergoes deamination, the amino group is removed, transforming cytosine into uracil (U). This reaction is facilitated by specific enzymes and can lead to errors during DNA replication if not corrected. In DNA, uracil is not a standard base, so its presence can lead to base-pair mismatches. If the uracil is not repaired before DNA replication, it can pair with adenine instead of guanine, resulting in a G:C to A:T transition mutation in subsequent cell divisions.
2. Implications of Deamination:
Deamination is a common form of DNA damage and occurs spontaneously, especially under physiological conditions. The accumulation of such mutations can lead to genetic instability, contributing to various diseases, including cancer.
3. Other Statements:
- A. Deamination of cytosine causes a transversion mutation: This is incorrect because deamination of cytosine leads to uracil, which results in a transition mutation, not a transversion.
- C. Deamination of cytosine results in thymine: This is incorrect because deamination of cytosine does not produce thymine; it produces uracil instead.
- D. Deamination of thymine results in uracil: This statement is misleading. Thymine can undergo deamination to form a different compound, but it is not commonly referred to in standard mutation processes.
In summary, deamination is a critical process in molecular biology, and recognizing its implications helps us understand mutation mechanisms and the importance of DNA repair mechanisms in maintaining genomic integrity.