apyrimidinic
adj.adj. Describing a spot in a DNA molecule where a pyrimidine base — cytosine or thymine — has gone missing, leaving an empty gap in the strand while the sugar-phosphate backbone stays intact. Together with apurinic spots these are called AP (apurinic/apyrimidinic) or abasic sites, and cells keep repair tools that hunt them down and patch them.
adj. Of a position in DNA: lacking a pyrimidine base (cytosine or thymine) while the sugar–phosphate backbone remains intact, producing an apyrimidinic (AP) or abasic site. Like apurinic lesions, these arise spontaneously or through DNA damage and, left unrepaired, can cause mutations or strand breaks; AP endonucleases recognise them and initiate base-excision repair.
An apyrimidinic site is a gap in DNA where a cytosine or thymine base has gone missing.
When a pyrimidine is lost from the strand, the apyrimidinic site left behind must be repaired before the cell copies its DNA.
AP endonucleases treat apyrimidinic sites like apurinic ones — nicking the backbone to launch the base-excision repair pathway that restores the missing base.
From a- (“without”) + pyrimidine + -ic — literally “without a pyrimidine.” Paired with apurinic to name DNA positions stripped of their base (together, AP sites).