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The Protein Helix
By Harold McGee
Published 2004
One effect of the peptide bond is a certain kind of regularity that causes the molecule as a whole to twist and form a spiral, or helix. Very few proteins exist as a simple regular helix, but those that do tend to join together in strong fibers. These include connective-tissue collagen in meat, an important factor in its tenderness, and the source of gelatin.
Amino acids and proteins, denaturation and coagulation. Top: Three of the 20-odd amino acids important in food. Each amino acid has a common end including an amino (NH2) group, by which amino acids bond to each other into long chains called proteins, and a variable end or “side group” that can form different kinds of bonds with other amino acids. Center: A chain of amino acids shown schematically, with some of the side groups projecting from the chain. The amino acid chain can fold back on itself, and some of the side groups form bonds with each other to hold the chain in a folded shape. Bottom: Heating and other cooking processes can break the fold-stabilizing bonds and cause the long chains to unfold, or denature (left, center). Eventually the exposed side groups form new bonds between different protein chains, and the proteins coagulate, or form a permanently bonded solid mass (right).