# apurinic

/ˌeɪpjʊˈrɪnɪk/ (US) · CEFR C2 · Adjective

Source: https://englishreference.com/word/apurinic
Updated: 2026-07-27

## Definition

Describing a spot in a DNA molecule where a purine base — adenine or guanine — has gone missing, leaving an empty gap in the strand while the sugar-phosphate backbone stays intact. Such spots are also called AP sites or abasic sites, and cells keep repair tools that hunt them down and patch them.

For teachers: Of a position in DNA: lacking a purine base (adenine or guanine) while the sugar–phosphate backbone remains intact, producing an apurinic (AP) or abasic site. These lesions arise spontaneously or through DNA damage and, left unrepaired, can cause mutations or strand breaks; AP endonucleases recognise them and initiate base-excision repair.

## Examples

- An apurinic site is a gap in DNA where a base has gone missing.
- When a purine drops out of the strand, the apurinic site left behind has to be repaired before the cell divides.
- AP endonucleases recognise apurinic sites and nick the backbone, launching the base-excision repair pathway that restores the missing nucleotide.

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