Essential Amino Acids in Diet

Amino acids are the building blocks of proteins and play crucial roles in various biological processes. Each amino acid has a specific structure, including an amino group, a carboxyl group, and a side chain (R group) that determines its properties. Understanding the relationship between an amino acid's structure and its role in protein function is key to grasping biochemistry.

Which of the following amino acids is classified as essential for humans, meaning it cannot be synthesized by the body and must be obtained through diet?