Glycine is present in
**Core Concept**
Glycine is a non-essential, non-polar amino acid that plays a crucial role in various physiological processes, including neurotransmission, collagen synthesis, and as a precursor to purines and glutathione. It is the simplest amino acid, with a single hydrogen atom as its side chain.
**Why the Correct Answer is Right**
Glycine is an inhibitory neurotransmitter in the central nervous system, acting on glycine receptors to produce an inhibitory postsynaptic potential (IPSP). It is also a precursor to glutathione, a tripeptide composed of glycine, glutamic acid, and cysteine, which is essential for antioxidant defenses and detoxification processes. Glycine is also involved in the synthesis of creatine, a high-energy compound found in muscle tissue.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because glycine is not primarily involved in the regulation of blood pressure.
**Option B:** Incorrect because glycine is not a precursor to serotonin.
**Option C:** Incorrect because glycine is not a stimulatory neurotransmitter.
**Clinical Pearl / High-Yield Fact**
Glycine is often used as an intravenous agent to reduce the risk of seizures during surgical procedures, particularly in patients with a history of seizure disorders.
**Correct Answer: D. Glycine is a neurotransmitter and a precursor to glutathione and creatine.**