Question

Which one is a component of ornithine cycle?
A) Ornithine, citrulline and alanine
B) Ornithine, citrulline and arginine
C) Amino acids are not used
D) Ornithine, citrulline and fumaric acid

Answer 1

Ornithine cycle which is also known as the urea cycle is a biochemical process that involves formation of urea from ammonia. Ammonia is highly toxic for the living system and hence it is converted to urea for excretion. Ornithine cycle takes place in the liver and to some less extent in the kidney.

Complete answer:
The ornithine cycle comprises four enzymatic reactions- one of them occurs in the mitochondria and the rest three in the cytosol. Before the cycle begins ammonia is converted to carbamoyl phosphate which enters into the cycle. The carbamoyl phosphate is then converted into citrulline followed by it’s conversion to argininosuccinate. Arginosuccinate then converts into arginine and fumarate and finally the arginine is cleaved to form urea and ornithine. This urea is then excreted out of the system. Many disorders are associated with the malfunctioning of the urea cycle like delirium, lethargy and also in some cases liver cirrhosis. Thus the regulation of the urea cycle should be carried out properly. The regulators of the urea cycle are mostly N-acetylglutamic acid and the different substrate concentrations.

Hence the correct answer is options (B).

Note: Urea cycle takes place mainly in ureotelic organisms and is a very important process to maintain the physiological conditions of the living system. Concentrations of all the substrates should be properly maintained so that the cycle can occur without any disturbance.