Final answer:
In base excision repair (BER), three main unique enzymes are DNA glycosylases, which remove damaged bases; AP endonuclease, which cleaves the DNA backbone; and DNA polymerase and DNA ligase, which fill in and seal the gap, restoring the DNA to its correct sequence.
Step-by-step explanation:
Base Excision Repair Enzymes and Their Functions
The base excision repair (BER) pathway involves multiple enzymes that play vital roles in correcting DNA damage. The three main unique enzymes involved in BER are:
- DNA glycosylases: These are a group of repair enzymes that initiate the repair process by recognizing and removing damaged bases from DNA. Each DNA glycosylase has specificity for certain types of damage. For example, some recognize oxidized or deaminated bases and hydrolyze the glycosidic bond between the base and the deoxyribose sugar, thus excising the incorrect base.
- AP (apurinic/apyrimidinic) endonuclease: After the removal of the damaged base by DNA glycosylase, an AP site is left behind. AP endonuclease cleaves the phosphodiester backbone at the AP site, which is necessary for the subsequent repair synthesis steps.
- DNA polymerase: DNA polymerase then synthesizes a new, correct DNA strand by adding nucleotides in place of the excised base and the removed segment.
- DNA ligase: Lastly, DNA ligase seals the remaining gap in the DNA backbone by forming a phosphodiester linkage, ensuring the continuity and integrity of the DNA molecule.
BER is a crucial mechanism for maintaining DNA stability and preventing mutations that may lead to various diseases, including cancer.