Question

How was ATP utilized in urea cycle?
A. 3 ATP$\to$ 2 ADP + 1 AMP
B. 2 ATP + 1 AMP$\to$ 1 ATP + 2 ADP
C. 2 ATP$\to$ 1 ADP + 1 AMP
D. 1ATP$\to$ 1 ADP

Answer 1

Urea cycle is the cycle of biochemical reactions that helps in producing urea from ammonia. The urea cycle helps in conversion of highly toxic ammonia into urea for excretion and occurs in ureotelic organisms. This cycle was the first ever metabolic cycle to be discovered, even five years before the discovery of the TCA cycle.

Complete answer:
Urea synthesis involves a five step cyclic process with five distinctive enzymes. The entire process converts two amino groups in which one from $N{H_4}$ and another from Aspartate, and a carbon atom from $HC{O_3}$ to relatively non-toxic product which is urea by consumption of four high energy phosphate bonds as 3 ATP hydrolyzed to 2 ADP and one AMP. Urea cycle utilizes 2ATP which is converted to 2 ADP + 2PPi for the formation of carbamoyl phosphate and third step utilizes 1 ATP which is changed into AMP + PPi for the production of argininosuccinate. Thus, the urea cycle utilizes 3 ATP$\to$ 2 ADP + 1 AMP. Amino acid catabolism results in waste material and all animals need to excrete this product out of the body. Organisms cannot easily remove the nitrogen as ammonia converts it to less toxic substances such as urea through the urea cycle in our body.

Hence, the correct option is A. 3 ATP$\to$ 2 ADP + 1 AMP.

Note: Urea cycle mainly in the liver of our body where urea is produced by the liver is released to the bloodstream where it travels into the kidney and urine is excreted. In insects and birds the ammonia is converted to uric acid which is excreted in solid form.