Proteins and folding
Amino acids share amino and carboxyl groups but differ in their side chains. Peptide bonds create the primary sequence. Hydrogen bonding between backbone groups stabilizes common secondary structures, while interactions involving side chains help stabilize tertiary structure. Multiple polypeptides can assemble into a quaternary structure. Hydrophobic side chains often become buried inside soluble proteins; charged and polar side chains can interact with water. Changes in temperature, pH, or sequence can alter folding and binding. Denaturation commonly disrupts higher-order structure without cleaving the entire peptide backbone.
Replacing a charged amino acid on an enzyme’s binding surface with a nonpolar amino acid can alter attraction to the substrate. The effect depends on location; not every substitution destroys a protein.
Denaturation does not automatically mean the amino acid sequence was changed. A protein can lose its functional shape while keeping its peptide bonds intact.