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The structure of proteins

The primary structure

The amino acid sequence is called the primary structure of a protein.

gly-his-lys is the primary structure of a tripeptide used in cosmetics ("anti-aging")

The secondary structure

The local folding of the peptide chain to an α helix, β sheet or random coil is called secondary structure.

 

The secondary structure is due to the attraction between polar carbonyl $C=O$ and amine groups $-NH-$

The tertiary structure

The shape due to the folding of the polypeptide chain in space is called tertiary structure of a protein.

 

The tertiary structure is due to - the disulfide bridges formed by oxidation between remote cysteines: - the elbow angles of the rigid amino acid proline - the dipole-dipole attractions between distant parts of the chain: The three-dimensional tertiary structure of a protein determines its function: When this structure is disturbed by the use of a denaturant, the protein loses its function: it is denatured.