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#deamination

2 public questions tagged with this topic.

Mutation and Mutagenesis

Deamination of adenine produces

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.

Ref: Lehninger Principles of Biochemistry, 8th ed., Chapter 8: Adenine Deamination to Hypoxanthine

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Mutation and Mutagenesis

Deamination of cytosine produces

Cytosine undergoes hydrolytic deamination at C4 position removing exocyclic amino group, producing uracil that normally resides exclusively in RNA. In DNA context, uracil pairs preferentially with adenine like thymine, so if replication proceeds before uracil-DNA glycosylase removes uracil via base excision repair, original G:C pair becomes A:U then A:T after second round, yielding C→T transition. Methylated 5-methylcytosine deaminates to thymine creating T:G mismatch that is less efficiently repaired, explaining CpG hypermutability. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 12: Cytosine Deamination to Uracil

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