Based on the map above, if one of the bases in a strand of DNA is damaged and needs to be replaced, what mechanism will the cell use to repair the DNA?

• A. Mismatch repair.
• B. Nucleotide excision repair.
• C. Base excision repair.
• D. Photoreactivation.

Answer: (C)

Verified step by step guidance

1. Understand the types of DNA damage: DNA can be damaged in various ways, such as mismatches, bulky adducts, or single base alterations. Each type of damage has a specific repair mechanism.
2. Identify the type of damage: In this problem, the damage involves a single base in the DNA strand. This suggests that the repair mechanism should specifically target small, non-helix-distorting base lesions.
3. Learn about base excision repair (BER): BER is a cellular mechanism that repairs damaged DNA throughout the cell cycle. It is responsible for fixing small, non-helix-distorting base lesions, such as those caused by oxidation, deamination, and alkylation.
4. Explore the steps of base excision repair: BER involves several steps, including recognition and removal of the damaged base by a DNA glycosylase, cutting of the DNA backbone by an AP endonuclease, and filling in the gap with the correct nucleotide by DNA polymerase and ligase.
5. Compare with other repair mechanisms: Mismatch repair fixes errors that occur during DNA replication, nucleotide excision repair deals with bulky helix-distorting lesions, and photoreactivation specifically repairs UV-induced damage. Base excision repair is the most suitable mechanism for single base damage.