BIO Lecture Notes - Lecture 1: Carbamoyl Phosphate, Urera, Ornithine
2 Nov 2022
Department
Course
Professor
Document Summary
The cycle is known as krebs-henseleit urea cycle. As ornithine is the first member of the reaction sequences, it is also called as ornithine cycle. The two nitrogen atoms of urea are derived from two different sources, one from ammonia and the other directly from aspartic acid. One molecule of ammonia condenses with co2 in the presence of two molecules of atp to form carbamoyl phosphate. The reaction is catalyzed by the mitochondrial enzyme carbamoyl phosphate synthetase-i (cps-i) Cps-i reaction is the rate-limiting step in urea formation. The carbamoyl group is transferred to the nh2 group of ornithine. Citrulline is neither present in tissue proteins nor in blood; but it is present in milk. One molecule of aspartic acid is added, which provides the 2nd nitrogen atom of urea. This needs hydrolysis of atp to amp level, so two high energy phosphate bonds are utilized. 4th steps taken together may be summarized as: citrulline + aspartate arginine + fumarate.
