Enzymes, which are usually proteins, are biological catalysts--agents that change the rate of a reaction but are unchanged by the reaction. The molecules, which an enzyme reacts with, are called substrate. Enzymes reduce the activation energy needed for a reaction. An active site is the specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds. Active sites can lower the activation energy of the reactants by providing suitable microenvironment, by binding to the substrate in such a way that the critical bond between the substrate are strained and by providing template for a substrate to come to a proper orientation.
When a substrate molecule enters the active site, the enzyme changes shape slightly, creating an induced fit between the substrate and active site. Enzymes catalyze a reaction by lowering the activation energy in a reaction.
The velocity of an enzyme-catalyzed reaction may be controlled by several factors as follows: Enzyme catalyzing rate increase with rising temperature up to a certain point, very high temperature denatures an enzyme.
An enzyme requires an optimum temperature for its activity, change in pH may denature an enzyme. Cofactors are small molecules that bind with enzymes and are necessary for enzyme catalytic function. They may be organic or inorganic. Vitamins are coenzymes. Enzymes by have competitive inhibitors or noncompetitive inhibitors, which change the conformation of the enzyme, thus impeding its functions. Competitive inhibitors battle for the active site of the enzyme. (O in photosynthesis). Non-competitive inhibitors bind to a part of the enzyme away from the active site and may also regulate an enzyme activity. Molecules that inhibit or activate enzyme activity may bind to an allosteric site, a receptor site separate from the active site. Allosteric enzymes may be critical regulators of metabolic pathways. Metabolic pathways are commonly...