Amino Acids, Proteins and Porphyrins
Which one of the following statements about the urea cycle is correct?
|A||The two nitrogen atoms that are incorporated into urea enter the cycle as ammonia and alanine.|
|B||Urea is produced directly by the hydrolysis of ornithine.|
|C||ATP is required for the reaction in which argininosuccinate is cleaved to form arginine.|
|D||Urinary urea is increased by a diet rich in protein.|
a. The amino nitrogen of dietary protein is excreted as urea. The two nitrogens enter the urea cycle as ammonia and aspartate.
b. Urea is produced by the hydrolysis of arginine. The cleavage of argininosuccinate does not require ATP. The urea cycle occurs partly in the mitochondria.