Enzymes for urea synthesis are present in:
**Core Concept**
The question is testing the knowledge of the urea cycle, also known as the ornithine cycle, which is a metabolic pathway that converts ammonia into urea. This process occurs primarily in the liver and is essential for the excretion of nitrogenous waste.
**Why the Correct Answer is Right**
The enzymes for urea synthesis are present in the mitochondria of the liver cells. The urea cycle involves a series of enzyme-catalyzed reactions that convert ammonia into urea, using ornithine as a substrate. The key enzymes involved in this process are carbamoyl phosphate synthetase I (CPS I), ornithine transcarbamylase (OTC), and argininosuccinate synthetase (ASS). These enzymes work together to convert ammonia into urea, which is then excreted into the bloodstream.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the enzymes for urea synthesis are not present in the kidneys. While the kidneys do play a role in the excretion of urea, the actual synthesis of urea occurs in the liver.
* **Option B:** This option is incorrect because the enzymes for urea synthesis are not present in the muscles. While muscles do contain some enzymes involved in nitrogen metabolism, they are not responsible for the synthesis of urea.
* **Option C:** This option is incorrect because the enzymes for urea synthesis are not present in the lungs. The lungs are primarily involved in the exchange of gases, such as oxygen and carbon dioxide, and are not directly involved in the synthesis of urea.
**Clinical Pearl / High-Yield Fact**
A deficiency in any of the enzymes involved in the urea cycle can lead to hyperammonemia, a condition characterized by elevated levels of ammonia in the blood. This can be life-threatening if left untreated, and is a key consideration in the diagnosis and management of patients with urea cycle disorders.
**Correct Answer: C. Liver**