Protein Structure

An enzyme is a protein molecule that functions as an organic catalyst to speed a chemical reaction. The structure of a protein has at least three levels of an organization, and can even have four. Each level can be thought of as a different phase. A polypeptide is a single chain of amino acids. A peptide is a bond that joins two amino acids.

First Level- Primary Structure

A linear sequence of the amino acids joined by peptide bonds (think of the structure like a necklace and the amino acids are the different beads).

Second Level- Secondary Structure

The second structure comes about when the polypeptide takes on a certain orientation in space, the structure is an alpha helix. Hydrogen bonding between peptide bongs holds the shape in place.

Third Level- Tertiary Structure

The structure is now finally a three-dimensional shape in this structure. The helix folds into a

characteristic globular shape due in part to covalent bonding between 'R' groups. ('R' groups are alanine, valine, cysteine, and phenylalnine.) The shape is maintained by various types of bonding; covalent, ionic, and hydrogen.

Fourth Level- Quaternary Structure

This level occurs when two or more polypeptides join to form a single protein.

Proteins, which have levels of organization, are important in the structure and the function of cells. Some proteins are enzymes, which speed chemical reactions.

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