Question

The first amino group entering into the urea cycle is

• A. Carbomyl phosphate
• B. Ornithine
• C. Citrulline
• D. Argininosuccinate

Hint:

Carbomyl phosphate is synthesized in the mitochondria and plays a critical role in the entry of nitrogen into the urea cycle.

Answer 1

The Correct Option is A

Step 1: Understanding the urea cycle.
The urea cycle is a metabolic pathway that eliminates excess nitrogen by converting ammonia into urea. The first amino group entering the cycle is derived from ammonia and is incorporated into carbomyl phosphate.
Step 2: Analyzing the options.
(1) Carbomyl phosphate: Correct — Carbomyl phosphate is the first intermediate in the urea cycle, where ammonia combines with CO2 to form this compound.
(2) Ornithine: Ornithine is an important intermediate in the cycle but does not carry the first amino group.
(3) Citrulline: Citrulline is formed later in the cycle but is not the first amino group carrier.
(4) Argininosuccinate: Argininosuccinate is formed after citrulline and is not the first intermediate.
Step 3: Conclusion.
The correct answer is (1) Carbomyl phosphate, as it carries the first amino group entering the urea cycle.