Page "Biochemistry" Paragraph 37

Like carbohydrates, some proteins perform largely structural roles.

For instance, movements of the proteins actin and myosin ultimately are responsible for the contraction of skeletal muscle.

One property many proteins have is that they specifically bind to a certain molecule or class of molecules — they may be extremely selective in what they bind.

Antibodies are an example of proteins that attach to one specific type of molecule.

In fact, the enzyme-linked immunosorbent assay ( ELISA ), which uses antibodies, is currently one of the most sensitive tests modern medicine uses to detect various biomolecules.

Probably the most important proteins, however, are the enzymes.

These molecules recognize specific reactant molecules called substrates ; they then catalyze the reaction between them.

By lowering the activation energy, the enzyme speeds up that reaction by a rate of 10 < sup > 11 </ sup > or more: a reaction that would normally take over 3, 000 years to complete spontaneously might take less than a second with an enzyme.

The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates.

Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.