What Are R-Groups and Why Do They Matter? (AHL)

R-groups are the variable side chains attached to the central alpha carbon of amino acids. They matter because their different chemical properties determine how a polypeptide folds into a precise three-dimensional shape and, therefore, how the protein functions.

This is additional higher level (AHL) content in IB Biology subtopic B1.2 Proteins. Every amino acid has the same generalized framework: an amino group, carboxyl group, hydrogen atom and R-group attached to an alpha carbon. It can be represented as $\text{H}_2\text{N}-\text{CH}(R)-\text{COOH}$ .

What Are R-Groups and Why Do They Matter? (AHL)

R-group property	Effect on protein structure
Polar	Can form hydrogen bonds with other polar groups or water
Charged	Can form ionic bonds with oppositely charged R-groups
Non-polar	Forms hydrophobic interactions and tends to avoid water
Cysteine R-group	Can form covalent disulfide bonds with another cysteine

What Are R-Groups and Why Do They Matter? (AHL)

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What Are R-Groups and Why Do They Matter? (AHL)