Tertiary Structure

When a proteins chain is folded in a three dimensional arrangement, a compact and tightly folded structure is formed and designated as tertiary structure. Most native proteins occur in this state and the shape is stabilized by intermolecular bonds of the following types so that the distant regions of the chain are brought closer. The folded proteins may be spherical, globular or ellipsoidal. The intermolecular bonds are :

1. Interpeptide hydrogen bonds
2. Sidechain hydrogen bonds
3. lonic bonds
4. Hydrophobic interactions NH₂

The tertiary structure describes the conformation of the entire protein. Myoglobin is the first protein whose tertiary structure was established by Kendrew using x-ray diffraction technique. It is an iron containing protein acting as storehouse of oxygen in the muscle which has 153 amino acid residues(MW­­­­­~ 17500). There are no SH group, hence disulphide bonds are absent. The myoglobin chain is folded back on itself in a complex arrangement without any symmetry within the molecule.

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