In mammalian tissue, glycine is synthesized from the following precursors:
**Core Concept**
The synthesis of glycine in mammalian tissue involves the conversion of a precursor molecule through a series of enzymatic reactions. Glycine is a non-essential amino acid that plays a crucial role in various biological processes, including protein synthesis, DNA synthesis, and neurotransmission.
**Why the Correct Answer is Right**
Glycine is synthesized from serine via the enzyme serine hydroxymethyltransferase (SHMT). This enzyme catalyzes the conversion of serine to glycine, releasing a molecule of 5,10-methylenetetrahydrofolate (5,10-CH2-THF) in the process. This reaction is an important step in the metabolism of serine and glycine, and it also provides a link between these two amino acids.
**Why Each Wrong Option is Incorrect**
* **Option A:** There is no known direct precursor for glycine synthesis in mammalian tissue.
* **Option B:** Threonine is an amino acid that is synthesized from glycine and acetyl-CoA, but it is not a precursor for glycine synthesis.
* **Option D:** Alanine is a non-essential amino acid that can be synthesized from pyruvate, but it is not a precursor for glycine synthesis.
**Clinical Pearl / High-Yield Fact**
Glycine is an inhibitory neurotransmitter that plays a crucial role in the regulation of motor neurons in the spinal cord. Its synthesis from serine is an important step in the metabolism of this neurotransmitter.
**Correct Answer:** C.