Enzymes

Almost every enzyme is a protein. There is, however, an important exception: certain nucleic acids can also act as enzymes, and these are called ribozymes. So while proteins dominate, catalytic ability is not the exclusive property of proteins.

An enzyme is a protein with all the usual levels of structure

Because a typical enzyme is a protein, it possesses the same structural levels as any other protein. It has a primary structure — its particular amino acid sequence. It also has a secondary structure and a tertiary structure. The tertiary level is where the action lies.

The active site

When the protein chain folds into its three-dimensional tertiary shape, the chain criss-crosses over itself. This folding creates various crevices and pockets on the surface of the molecule. One of these pockets is special and is known as the active site.

• The active site is a crevice or pocket into which the substrate — the molecule the enzyme acts on — fits.
• It is through this active site that an enzyme grips its substrate and catalyses the reaction at a high rate.

How enzymes differ from inorganic catalysts

Enzymes are catalysts, but they are not like the inorganic catalysts of ordinary chemistry, and there are several differences. One of the most important concerns temperature:

• Inorganic catalysts typically work best at high temperatures and high pressures.
• Enzymes are damaged by high temperatures. Most enzymes get spoiled above about 40 degrees Celsius, because heat destroys the delicate protein folding they depend on.

Enzymes from heat-loving organisms …