Urea Cycle & Pyrimidine Synthesis Flashcards

Urea Cycle & Pyrimidine Synthesis Flashcards

What molecule connects the urea cycle and pyrimidine synthesis?

Carbamoyl phosphate

Which enzyme makes carbamoyl phosphate in the urea cycle?

Carbamoyl phosphate synthetase I (CPS I)

Which enzyme makes carbamoyl phosphate in pyrimidine synthesis?

Carbamoyl phosphate synthetase II (CPS II)

Where is CPS I located?

Mitochondria

Where is CPS II located?

Cytoplasm

What nitrogen source does CPS I use?

Free ammonia (NH₃)

What nitrogen source does CPS II use?

Glutamine

Main function of CPS I?

Ammonia detoxification through the urea cycle

Main function of CPS II?

Pyrimidine nucleotide synthesis

Which CPS enzyme is activated by N-acetylglutamate?

CPS I

What happens in Ornithine transcarbamylase deficiency?

Carbamoyl phosphate accumulates and enters pyrimidine synthesis → increased orotic acid

Hyperammonemia + high orotic acid suggests what disease?

OTC deficiency

Why is orotic acid elevated in OTC deficiency?

Excess carbamoyl phosphate is diverted into pyrimidine synthesis

Which pathway removes toxic ammonia?

Urea cycle

Which pathway produces UMP, UDP, and UTP?

Pyrimidine synthesis