Question

The deamination of cytosine generates a uracil base. This is a naturally occurring nucleic acid base, and so does not represent a DNA lesion caused by damage due to chemicals or irradiation. Why is this base recognized as "foreign" and why is it important for cells to have a mechanism to recognize and remove uracil when it is found in the DNA duplex?

Answer 1

The removal of uracil from DNA is vital because uracil is not normally present in DNA and its presence due to deamination can lead to base substitution mutations, which the cell's repair mechanisms, such as uracil-DNA glycosylase, work to correct.

Step-by-step explanation:

The recognition and removal of uracil from DNA is crucial because uracil is normally found in RNA, not DNA. In DNA, uracil is recognized as a foreign base because deamination of cytosine can mistakenly lead to uracil incorporation, which can then pair with adenine instead of guanine during DNA replication. This leads to a base substitution mutation, specifically a G-C to A-T transition, which alters the genetic information. To prevent this, cells have repair mechanisms, including the enzyme uracil-DNA glycosylase, that recognize uracil and facilitate its removal and replacement with cytosine, restoring the DNA's correct sequence.

Deamination is a natural process, happening approximately 100 times per day per cell, leading to the potential for mutations if not corrected. The uracil-DNA glycosylase enzyme is vital for maintaining genomic stability by correcting such errors, preventing a raft of potential downstream problems resulting from incorrect protein synthesis.