Denaturation and enzymes

A native protein is one in its natural three-dimensional shape with its biological activity. A physical change (temperature) or chemical change (pH) disturbs its hydrogen bonds, globules unfold, helices uncoil, and the activity is lost: denaturation.

In denaturation the secondary and tertiary structures are destroyed but the primary structure, the sequence held by peptide bonds, survives.

Everyday cases: egg white setting on boiling, and milk curdling when its bacteria make lactic acid.

Enzymes are biocatalysts that let the body's reactions run under mild conditions. Almost all are globular proteins, and each is highly specific to one reaction and one substrate.

Names usually come from the substrate plus -ase: maltase hydrolyses maltose, C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆ (glucose). Some come from the reaction: oxidoreductases catalyse oxidation of one substrate with reduction of another.

Enzymes are needed only in small amounts and, like chemical catalysts, lower the activation energy. NCERT's example: acid hydrolysis of sucrose has Ea 6.22 kJ mol⁻¹, hydrolysis by sucrase only 2.15 kJ mol⁻¹.