Chemistry · Ch 10 — Biomolecules
Denaturation of Proteins
Denaturation of Proteins
A protein that exists in a biological system with its own unique three-dimensional structure and full biological activity is called a native protein. This native shape is not arbitrary — it is the specific folded conformation (secondary + tertiary, and where relevant quaternary, structure) in which the protein performs its biological role.
What Happens During Denaturation
When a native protein is subjected to a physical change, such as a change in temperature, or a chemical change, such as a change in pH, the hydrogen bonds that hold its folded conformation together are disturbed. As a direct consequence:
- globular proteins unfold — the compact spherical globule opens up, and
- helical regions uncoil — the α-helix loses its regular coiled arrangement.
As these structural bonds are broken, the protein loses its biological activity. This overall process — the disruption of a native protein's shape and function through disturbance of its stabilising hydrogen bonds — is called denaturation of the protein.
Only the Higher-Order Structure Is Lost
During denaturation, it is specifically the secondary and tertiary structures of the protein that are destroyed. The primary structure — the actual sequence in which the amino acids are linked to one another along the chain — remains intact. Denaturation rearranges and disrupts the folding of the chain; it does not break the peptide bonds joining one amino acid to the next, so the underlying amino-acid sequence is unaffected even though the protein's shape and function are destroyed.
What denaturation destroys — and what it does not
- Destroyed: secondary structure (α-helix/β-pleated sheet folding pattern) and tertiary structure (overall 3-D folding) — along with these, the protein's biological activity.
- Left intact: the primary structure — the amino-acid sequence itself is unchanged; only how the chain is folded/coiled is affected, not what it is made of or the order of its links.