Base excision repair BER is a crucial DNA repair mechanism that maintains the integrity of DNA during replication and prevents mutations. It is responsible for detecting and repairing small-scale DNA damage, such as damaged or incorrect bases, which can occur due to various factors like oxidation, alkylation, or deamination.The base excision repair mechanism involves several steps:1. Recognition of damaged base: The first step in BER is the recognition of the damaged or incorrect base by a DNA glycosylase enzyme. There are several types of DNA glycosylases, each specialized in recognizing and removing specific types of damaged bases.2. Removal of damaged base: Once the damaged base is recognized, the DNA glycosylase enzyme cleaves the N-glycosidic bond between the damaged base and the sugar-phosphate backbone of the DNA. This results in the removal of the damaged base, leaving behind an abasic site also known as an AP site .3. Cleavage of the DNA backbone: The next step involves the cleavage of the DNA backbone at the abasic site. An enzyme called AP endonuclease recognizes the AP site and cleaves the phosphodiester bond on the 5' side of the abasic site, generating a single-strand break with a 3'-hydroxyl group and a 5'-deoxyribose phosphate 5'-dRP group.4. Repair synthesis: DNA polymerase, a specialized enzyme, then adds the correct nucleotide to the 3'-hydroxyl group at the single-strand break. In some cases, DNA polymerase can also remove the 5'-dRP group, while in other cases, a separate enzyme called dRP lyase is required for its removal.5. Ligation: Finally, the remaining nick in the DNA backbone is sealed by DNA ligase, an enzyme that catalyzes the formation of a phosphodiester bond between the 3'-hydroxyl group and the 5'-phosphate group, thus restoring the integrity of the DNA molecule.By following these steps, the base excision repair mechanism effectively detects and corrects small-scale DNA damage, ensuring the accurate replication of DNA and preventing the accumulation of mutations that could lead to various diseases, including cancer.