An enzyme is a biochemical catalyst. A catalyst is a chemical which is involved in a chemical reaction, and changes its rate – usually making it faster – without being chemically altered in the process. So, enzymes get involved in biochemical reactions, in many instances allowing reactions to occur which never would have occurred otherwise.
Specifically-shaped Proteins
Enzymes are proteins – very large polymer molecules made from monomers called amino acids. The sequence of amino acids in each protein is absolutely crucial, because it determines what is called the secondary and tertiary structure of the protein, or how it folds up. Each amino acid has a group of atoms which have certain properties. Some are very small, while others are larger and more bulky. Some are more hydrophilic (attracting to water) and some are hydrophobic (hate water). Some have an electrical charge which allows the formation of hydrogen bonds.
Thus, the order of amino acids in a protein molecule determines both the way it can fold up, and the properties of the resulting shape. This is especially important for enzymes, which have to have very specific properties in order to facilitate very specific biochemical reactions.
Enzyme Active Sites
The key to understanding how an enzyme works is found in the idea of an active site. In order to catalyse a biochemical reaction, the enzyme must bind to one or more of the substrates involved in the reaction. It does this by having a very specifically-shaped active site, where the substrates attach.
Lock and Key
The active site of an enzyme can be explained using the example of a lock and key. In order to operate a lock, a specifically shaped key must be used. Any key that is too big, two small or with the wrong pattern of teeth will not operate the lock. The active site of an enzyme is the same. It has a specific shape and size, with a particular electronic orientation. This means that only one molecule, or a small number of molecules, will fit the active site of each enzyme
Induced Fit Theory
Some interactions of substrates with enzyme are not fully explained by the lock and key analogy, so a further theory has been developed called the induced fit theory. In this theory, the idea that the substrate actually affects the final shape of the active site is proposed. An enzyme is flexible, so when a substrate binds, other parts of the enzyme may be altered. This explains why some compounds are bound to enzymes but do not react – they distort the shape of the enzyme too much.
A lot of research goes into determining the mechanisms involved in enzyme-catalysed reactions. Each enzyme is very specific in the reaction it is involved with, so each reaction mechanism is very different. Many reactions have, however, been determined, allowing biochemists to understand a lot of the reactions which occur in living organisms.
Sources:
Charles E Ophardt, Mechanism of Enzyme Action, Virtual Chembook, Elmhurst College, elmhurst.edu
Simon Davies - Simon Davies has lived a varied life so far After completing a BSc in Chemistry at the University of Bristol, UK, he worked as a ...
Join the Conversation