Enzymes Essay, Research Paper

Enzymes are proteins, composed of polypeptide chains and non-protein

groups. Their function is to help with the reactions of many cells and

molecules by serving as catalysts. A catalyst is a substance that allows the

activation energy required for a reaction by forming a temporary association

with the molecules that are reacting. During this process, the catalyst itself is

not permanently altered in the process, and so it can be used over and over

again. Because of catalysts, cells are able to carry out chemical reactions at a

great speed and at comparative low temperatures.

Almost 2,000 different enzymes are now known, each of them capable

of catalyzing a specific chemical reaction. The molecule (s) on which an

enzyme acts is known as its substrate. For example, sucrose is the substrate

for the enzyme sucrase. Enzymes have specific structures that only its

specific substrate will fit into. The polypeptide chains of an enzyme are

folded in such way that they form a grove or pocket on the surface. The

substrate fits in to this grove, which is the site of reactions catalyzed by the

enzyme, or active site. Recent studies of enzyme structure have suggested

that the active site is flexible. The binding between enzymes and substrate

appears to alter the shape of the enzyme. This induces a close fit between the

active site and the substrate. It is also believed that this may put some strain

on the substrate molecule facilitating the reaction.

Another characteristics of enzymes are competitive inhibition and

non-competitive inhibition. Competitive inhibition is the binding of a

competitive molecule to the active site of the enzyme. This prevents the

proper substrate from reacting with the enzyme. In non-competitive

inhibition the binding of a non-competitive inhibitor to another site on the

enzyme induces an allosteric change, or conformational change, that prevents

the active site from binding to the proper substrate. An allosteric change

could be either a negative modulator or a positive effector. There?s also

cooperativity. This is the binding at an active site that makes the others more

reactive. An example to this is hemoglobin. Co-enzymes are also factors of

enzymes. These are heme-groups or prosthetic groups that bind to the

enzymes loosely as part of the reactions, such as vitamins.