**Question:** Amide-containing amino acid

**Core Concept:** Amide-containing amino acids are a type of amino acids that have an amide group (-CONH2) connecting the alpha-carbon to the side chain. This amide group is formed due to the condensation reaction between an alpha-keto acid and an amino acid, forming an amide bond.

**Why the Correct Answer is Right:** The correct answer, **D-Proline**, is an amide-containing amino acid. D-Proline is an L-amino acid, but it has an L-configuration at the alpha-carbon. The amide group (-CONH2) is present due to the condensation reaction between D-alanine and D-pipecolic acid, forming a proline molecule.

**Why Each Wrong Option is Incorrect:**

A. **L-Proline (Option A)**: This is incorrect because L-proline is a non-amide-containing amino acid. It forms due to the condensation between L-alanine and glycine, resulting in an L-configuration at the alpha-carbon.

B. **Glycine (Option B)**: Glycine is a non-amide-containing amino acid, which forms due to the condensation between α-ketoglutarate and ammonia, resulting in an L-configuration at the alpha-carbon.

C. **L-Alanine (Option C)**: L-alanine is a non-amide-containing amino acid, which forms due to the condensation between pyruvate and ammonia, resulting in an L-configuration at the alpha-carbon.

D. **D-Proline (Option D)**: This is the correct answer, as explained above.

**Clinical Pearl:** Amino acids are essential building blocks for proteins. The stereochemistry of amino acids, specifically the configuration of the alpha-carbon, determines whether they are amide-containing or non-amide-containing. Amino acids with an L-configuration at the alpha-carbon are found in proteins, while D-amino acids, like D-proline, are rare and have specific roles in certain organisms, like bacteria and archaea, where they serve as building blocks for their cell walls.