Practice question

Deamination of adenine at C6 position converts adenine to hypoxanthine, purine retaining six-membered ring but bearing O6 carbonyl instead of amino group, resembling guanine pairing behavior. Hypoxanthine forms stable base pair with cytosine through two hydrogen bonds rather than thymine, prompting incorporation of C opposite lesion during replication. Subsequent synthesis places G opposite C, converting original A:T to G:C transition. Nitrous acid and alkaline conditions promote such deamination, and hypoxanthine removal relies on alkyladenine glycosylase in base excision repair. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.