Question

Which of these statements are true regarding the urea cycle?
1.Fumarate acts as a connecting link between the urea cycle and the Krebs cycle.
2.Urea cycle solely occurs in mitochondria only.
3.Citrulline and arginine react to form argininosuccinate.
4.Ornithine formed in the last reaction is directly excreted along with urea.
5.Arginase promotes cleavage of arginine to urea and ornithine.
(a)1,2,5
(b)1,2
(c)3,4
(d)1,5

Answer 1

The cycle of biochemical reactions which results in the production of Urea from ammonia is known as the urea cycle or the ornithine cycle. It helps in the conversion of highly toxic ammonia to urea for excretion.

Complete answer:
The side product formed during the cleavage of argininosuccinate is Fumarate along with arginine. The condensation reaction of Citrulline and aspartate forms argininosuccinate by the consumption of adenosine triphosphate. The urea cycle takes place in ureotelic organisms which convert highly toxic ammonia to urea for excretion. The urea cycle is performed in the liver and Kidney to a lesser extent. Ammonia is released as waste during amino acid catabolism and all animals excrete this product. Organisms that are unable to remove nitrogen as ammonia safely and easily they convert it into urea which is a less toxic substance by performing the urea cycle which occurs in the liver.

Additional Information: The urea is excreted by the organism in the bloodstream which travels through the Kidneys and is excreted out as urine. It is essential to perform a urea cycle for this organism as if the nitrogen or ammonia cannot be eliminated they can be detrimental to the organism. About 35000 people are affected by the urea cycle disorders which involves the genetic defect in enzymes and gets manifested within a few days after birth. It can result in coma or brain damage and have a higher risk of complications or death in newborns. Lethargy and delirium are symptoms that can result in urea cycle disorders and are similar to those of a stroke. The symptoms include malfunctioning in the liver of the patient which can obtain cirrhosis and can lead to sarcopenia which is the loss of muscle mass.

So, the correct answer is '1,5'.

Note: The urea cycle is performed to eliminate toxic ammonia from the body. A healthy adult removes 10 to 20 grams of ammonia every day. One in 3000 newborns is affected by urea cycle disorder which is genetic. It causes itching redness or irritation and can be worsened if not treated.