Practice question

Depurination is hydrolytic cleavage of N-glycosidic linkage between purine base and deoxyribose sugar, leaving apurinic AP site where backbone remains continuous but coding information absent. Spontaneous depurination occurs thousands of times daily per cell due to intrinsic lability of purine glycosidic bond, enhanced by acidic pH or alkylation. AP sites block replicative polymerases or follow A-rule where adenine preferentially inserted opposite non-instructional site, leading to transversion if opposite nucleotide not repaired by AP endonuclease initiated base excision. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.