Read the Assertion (X) and Reason (Y) statements carefully and select the correct option. Assertion (X) : DNA glycosylases play a central role in base excision repair. Reason (Y) : DNA glycosylases remove the entire damaged nucleotide along with its phosphate group from the DNA backbone.
X is true, but Y is false
Base excision repair begins when a lesion-specific DNA glycosylase (e.g. uracil-DNA glycosylase, OGG1) recognises a damaged base, so the assertion is true.
The glycosylase cleaves only the N-glycosidic bond between the base and deoxyribose, leaving an abasic (AP) site with the sugar–phosphate backbone intact; AP endonuclease then nicks the backbone and DNA polymerase β and ligase complete repair.
Removal of a whole nucleotide stretch with its phosphates is the work of nucleases in nucleotide excision repair, not of glycosylases, so the reason is false.
Therefore the assertion is true but the reason is false.
Hence, X is true, but Y is false.
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