Protein Denaturation

What is protein denaturation?

Protein denaturation is the loss of a protein’s specific three-dimensional structure (secondary, tertiary, or quaternary) caused by external stress such as heat, pH, or chemicals.
Denatured proteins unfold and lose their biological function, though their primary structure (amino acid sequence) remains intact.

What factors cause protein denaturation, and how do they disrupt bonds?

Heat:

• Increases molecular vibrations → breaks hydrogen bonds and hydrophobic interactions.

• Example: cooking egg white — albumin unfolds and coagulates.

2. pH changes:

• Alters the ionization of R groups, breaking ionic bonds and disrupting electrostatic interactions.

• Example: stomach acid denaturing dietary proteins for digestion.

3. Chemicals:

• Alcohols, urea, detergents, heavy metals bind to side chains, disturbing noncovalent bonds and disulfide bridges.

• Example: mercury (Hg²⁺) or lead (Pb²⁺) denatures proteins by binding to sulfhydryl groups (–SH).

4. Mechanical agitation:

• Vigorous shaking (e.g., whipping egg whites) breaks weak interactions.

What happens to enzyme activity when denaturation occurs?

Enzymes rely on precise 3D structure for active site specificity.
When denatured:

• The active site shape changes or is destroyed.

• Substrates can no longer bind properly.

• Catalytic activity stops.

Can denaturation ever be reversed (renaturation)?

Sometimes — mild denaturation can be reversible if conditions return to normal before aggregation occurs.

How does denaturation relate to biological homeostasis?

Cells must maintain optimal temperature and pH so proteins stay in their functional shape.

• Fever or acidosis (low blood pH) can cause partial protein denaturation, impairing enzymes and hormones.

• Homeostatic mechanisms (like sweating or buffering systems) prevent such structural disruption.