Glycine is used in the synthesis of all EXCEPT-
**Core Concept**
Glycine is a non-essential amino acid that serves as a precursor for various biomolecules, playing a crucial role in the synthesis of proteins, nucleotides, and other compounds.
**Why the Correct Answer is Right**
Glycine is involved in the synthesis of glutathione, porphyrins, creatine, and purines. However, it is not directly involved in the synthesis of glutamine. Glutamine is synthesized from glutamate via the action of the enzyme glutamine synthetase, which catalyzes the condensation of glutamate and ammonia to form glutamine.
**Why Each Wrong Option is Incorrect**
**Option A:** Glycine is indeed a precursor for glutathione, a tripeptide composed of cysteine, glycine, and glutamate.
**Option B:** Glycine is involved in the synthesis of porphyrins, which are the building blocks of heme.
**Option C:** Glycine is a precursor for creatine, a high-energy compound found in muscles.
**Option D:** Glycine is involved in the synthesis of purines, the nitrogenous bases found in DNA and RNA.
**Clinical Pearl / High-Yield Fact**
Glycine is the simplest amino acid and serves as a precursor for various biomolecules, making it an essential component of various biochemical pathways.
**Correct Answer:** D.