This refers to how enzymes in the body work. Enzymes are catalysts ie they speed up a reaction that would otherwise take months to occur without depleting themselves. They have an area called the active site that brings the reactive parts of the substrate molecules together - thus "clicking" them together or breaking them apart. They temporarily form an enzyme substrate complex then release the product of the reaction. This is called the lock and key theory of enzymes !
One of the early biochemist, Professor Fischer, illustrates an example of lock and key. It is only possible that unlock the lock when the wards of key fit exactly into the keyhole. The enzyme is a lock with a very specific keyhole, the substrate is the key. In addition the unlocking process can only be carried out in one particular way, similarly key must either turn to be left or right so that a bolt can open or a faucet can be turned on end off. Likewise, the enzyme produces one specific action in order that so me other useful function can occur.
The logical question which now has to be faced is "since there are so many different substrates and so many different reactions are requiring their own specific enzymes, how many different types of enzymes do our bodies require?"
This is the question that which enzyme researchers are still addressing themselves. Only one enzyme was known in 1831. in 1930, the number had risen to a total of 80. By 1984, approximately 2500 enzymes had been classified, sub classified and sub classified. In 1993, approximately 3000 enzymes are recognized. The end of the search is now where in the sight, even though some scientists think they see light at the end of the tunnel.
