Which of the following amino acid is used in biosynthesis of purines?
**Core Concept**
The biosynthesis of purines involves a complex pathway that requires specific amino acids as precursors. **Glycine**, **glutamine**, **aspartate**, and **carbon dioxide** are among the key molecules used in this process. The purine ring is constructed step by step, with each step requiring specific enzymes and substrates.
**Why the Correct Answer is Right**
Glycine is directly involved in the initiation of purine biosynthesis, providing two carbon atoms and one nitrogen atom to the purine ring. The process begins with the formation of **5-phosphoribosyl-1-pyrophosphate (PRPP)**, which then reacts with **glycine** to form **5-phosphoribosylglycinamide**. This step is crucial for the subsequent addition of other carbon and nitrogen atoms to form the purine ring.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is not directly related to the primary biosynthetic pathway of purines.
**Option B:** While important in other metabolic pathways, it is not the correct answer for purine biosynthesis.
**Option D:** Similar to option A, it does not directly contribute to the purine ring structure in the context provided.
**Clinical Pearl / High-Yield Fact**
Remembering that **glycine** is a critical starting material for purine biosynthesis is key. Disorders affecting purine metabolism can lead to significant clinical issues, such as **gout**, which is caused by excess **uric acid** production.
**Correct Answer:** D. Glycine