The primary factor that differentiates one amino acid from another is the structure of their side chains, known as R groups.
Amino acids, the building blocks of proteins, all share a common backbone structure that includes an amino group, a carboxyl group, and a central carbon atom. What makes each of the 20 standard amino acids unique is the specific chemical structure of its side chain, or R group. These side chains can vary significantly in size, shape, charge, and polarity, leading to different chemical properties and behaviors.
For instance, some amino acids have nonpolar side chains, making them hydrophobic and likely to avoid water, while others have polar or charged side chains, which are hydrophilic and can interact favorably with water. This diversity in the side chains is crucial for the structure and function of proteins, as it influences how proteins fold, how they interact with other molecules, and ultimately, their role in biological processes.