Denaturation
The loss of a protein's native three-dimensional structure without breaking its peptide bonds.
Unit
Dimensionless
In depth
Heat, extremes of pH, heavy metal ions, organic solvents and mechanical agitation all disrupt the weak interactions holding a protein folded. The primary structure survives, but function is lost, and for most proteins the change is irreversible.
Examples in the real world
Egg white turning opaque and solid on cooking; milk curdling in acid; alcohol denaturing bacterial proteins.