Tertiary Structure
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Tertiary Structure

On this page we'll take a look at the tertiary structure of proteins. You will find that it involves the interaction between the side groups of amino acid residues from different parts of the same chain.

A telephone cord, specifically the coil of a telephone cord, can be used as an analogy to the alpha helix secondary structure of a protein.

Telephone cord used as a model for alpha helix secondary structure. [68043.jpg]
You know as well as I do, that telephone cords also have a tertiary structure. The tertiary structure of a protein refers to the way the secondary structure folds back upon itself or twists around to form a three-dimensional structure. The secondary coil structure is still there, but the tertiary tangle has been superimposed on it.

Telephone cord used as model for tertiary structure. [68044.jpg]

Myoglobin

The tertiary structure for myoglobin is fairly well understood and is shown here. Myoglobin has an alpha helix which then can be viewed as being enclosed in this blue sheath, the sheath doesn't exist but we can draw it that way. That helix folds back upon itself into what's referred to as the tertiary structure of myoglobin. Bonds between the side groups of the amino acid residues are responsible for holding together the tertiary structure of this protein.

Diagram of myoglobin. [myog.jpg]

Bond Types Stabilizing Tertiary Structure

The kinds of bonds that can exist between the side groups include:

Van der Waals bonds if the side groups are nonpolar.
Hydrogen bonds if the side groups contain hydroxyl or amino groups.
Ionic bonds if the side groups are acids and bases that can transfer protons from one to another making a carboxylate ion, which is negative, and essentially an ammonium or quaternary ammonium ion which is positive.
Covalent bonds if the side groups are cysteine residues in which the sulfur atoms are bonded together by the removal of two hydrogen atoms.

In summary, the tertiary structure of a protein is held together by the bonds formed by the side groups, and there is quite a variety of different bonds that can cause the tertiary structure to form.

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E-mail instructor: Sue Eggling

Clackamas Community College
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