Question

Urea formation takes place through
a. Nitrogen cycle
b. Ornithine cycle
c. Cori cycle
d. Kreb's cycle

Answer 1

Urea formation through cycle occurs in ureotelic animals. The cycle converts highly toxic ammonia into urea and excretes it from the body. Urea formation cycle is the first metabolic cycle which was discovered five years before the discovery of the tricarboxylic acid cycle.

Complete answer:
Nitrogen cycle:
The nitrogen cycle, that is, the cycle of nitrogen in various forms in nature. Nitrogen, a component of proteins and nucleic acids, is essential for life on Earth. Although seventy-eight per cent of the atmosphere is nitrogen gas, this rich reservoir exists in a form that most organisms cannot use. However, as a result of a series of microbial transformations, the plants received nitrogen, which again supported the life of animals. Completely incompatible levels have been classified such as nitrogen fixation, nitrogen assimilation, ammonia, nitrification and denitrification.

Ornithine cycle:
Ornithine cycle is a metabolic pathway that converts nitrogen into urea, which is excreted by the body. Excretion takes place from the body in the form of urine. Ammonia, which is very toxic to humans, turns into urea, which is non-toxic, readily soluble and easily excreted by the kidneys.

Cori cycle:
The Cori Cycle (also known as the Lactic Acid Cycle), named after pioneers Carl Ferdinand Corey and Gertie Corey, is a metabolic pathway by which lactic acid produced during anaerobic muscle glycolysis is transported to the liver and converted to glucose. It then returns to the muscles and is cyclically metabolized back to lactic acid.

Kreb's cycle:
The TCA cycle or Krebs cycle is a series of cyclic reactions in which pyruvic acid produced by EMP and EDP is oxidized. The cycle acts on aerobic organisms, including animals, plants and microorganisms. The main function of this cycle is to generate energy through the oxidation of acetic acid. Acetic acid is obtained by decarboxylation of pyruvate and introduced into the TCA cycle as acetyl-CoA.

Hence, the correct answer is option (B).

Note: This period occurs mainly in the liver. The daily production of urea in the urine is twenty to thirty gram. Small amounts are excreted through sweat. The amount of urea excreted is proportional to total protein metabolism. Urea excretion is reduced in some liver diseases. In severe acidosis, urea production is reduced. In nephritis, blood urea levels increase when the kidneys' ability to excrete urea is severely impaired (uremic).