Final answer:
Amino acids differ from one another based on their R groups or side chains. These groups determine the amino acid's properties, such as polarity and charge, which influence how amino acids interact and their role in protein structures.
Step-by-step explanation:
The Distinction of Amino Acids
There are 20 different amino acids that are used by living organisms to form proteins. What makes each of the amino acids distinct is the variability of their side chains, also known as the R groups or side chains. While the core structure of amino acids—a central carbon bonded to an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and the R group—is the same, the R group differentiates them by varying in size, polarity, and electrical charge. For example, valine, methionine, and alanine are characterized by nonpolar or hydrophobic R groups, whereas serine, threonine, and cysteine have polar, hydrophilic side chains. The side chains of lysine and arginine, which are positively charged, further illustrate the diversity among amino acids.
The chemical nature of each amino acid's R group affects how it interacts with other molecules and thus determines its role in proteins and its overall function within an organism. Due to the importance of R groups, understanding these variations is crucial for studying protein structure and function.