**Core Concept**
Glycine is an amino acid with a crucial role in various biochemical pathways, particularly in purine and heme synthesis. It serves as a precursor for the synthesis of creatine, which is essential for muscle contraction and energy storage.

**Why the Correct Answer is Right**
Glycine is directly involved in the synthesis of purines, which are essential for DNA and RNA formation. It is also a key component in the synthesis of heme, a vital molecule for hemoglobin and other hemoproteins. However, glycine is not directly involved in the synthesis of spermine, a polyamine that plays a role in cell growth and proliferation. Spermine is synthesized from putrescine through the action of the enzyme spermidine synthase.

**Why Each Wrong Option is Incorrect**
**Option A:** Purine synthesis is indeed a pathway in which glycine plays a crucial role, serving as a precursor for the formation of purine nucleotides.
**Option B:** Creatine synthesis also involves glycine, which is converted into creatine through a series of reactions involving the enzyme arginine-glycine amidinotransferase.
**Option D:** Heme synthesis, like purine synthesis, involves glycine as a precursor molecule, which is incorporated into the heme ring through the action of the enzyme aminolevulinic acid synthase.

**Clinical Pearl / High-Yield Fact**
Glycine is also involved in the synthesis of glutathione, a tripeptide that serves as an antioxidant and plays a crucial role in cellular detoxification processes.

✓ Correct Answer: C. Spermine synthesis