Creatinine, NO & urea are synthesized from which amino acid?
**Core Concept**
The question tests the student's knowledge of nitrogenous waste metabolism, specifically the biosynthesis of creatinine, nitric oxide (NO), and urea. These compounds are crucial in understanding renal function and nitrogen balance in the body.
**Why the Correct Answer is Right**
The correct answer is related to the amino acid that serves as a precursor for these nitrogenous wastes. Creatinine is a breakdown product of creatine, which is synthesized from **arginine** and glycine. Nitric oxide (NO) is produced from **arginine** via the action of nitric oxide synthase. Urea, on the other hand, is synthesized in the liver through the urea cycle, which also involves **arginine** as a key intermediate.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because, although involved in various metabolic pathways, it is not directly related to the synthesis of creatinine, NO, and urea.
**Option B:** Incorrect as it is not the primary amino acid from which these compounds are synthesized.
**Option C:** Incorrect because, despite being an amino acid, it is not directly involved in the synthesis of these nitrogenous wastes.
**Clinical Pearl / High-Yield Fact**
Remember that **arginine** plays a central role in the metabolism of nitrogenous wastes, including the synthesis of creatinine, NO, and urea. This knowledge is essential for understanding renal function and various clinical conditions related to nitrogen balance.
**Correct Answer:** D. Arginine