Enzymes: Catalysts For Chemical Reactions

Enzymes Enzymes are catalysts for chemical reactions. They speed up these chemical reactions by lowering activation energy (energy required to start a chemical reaction.) Enzymes do not undergo permanent changes, so they are unchanged at the end of the reaction; they can only alter the rate of the reaction. Enzymes usually only catalyze specific reactions because of the shapes of the enzyme molecules. Many enzymes consist of a protein and the cofactor, which is a non-protein. The intramolecular and intermolecular bonds in the secondary and tertiary structures are disrupted by changes in temperature and pH. Changes in temperature and pH affect the shapes of enzymes, so the activity of the enzyme is pH and temperature sensitive. Some cofactors of enzymes are prosthetic groups (organic groups that are permanently bound to the enzyme,)

These molecules must collide with enough energy to overcome the energy barrier to reaction (activation energy.) The activation energy is the minimum amount of energy required for two molecules to undergo a reaction. The active site of an enzyme has the right shape and functional groups to bind to the reacting molecule called the substrate. A simple model to represent how an enzyme works is the lock and key analogy. In this example, the enzyme is the lock, and the key is the substrate. Locks and keys are specific to each other, in the same way that enzymes and substrates are specific to each other. A theory proposed by Daniel Koshland in 1958, the induced-fit model, says that the active site and substrate are not originally perfect matches for each other. He said that when the active site of the enzymes makes contact with the correct substrate, the enzyme molds itself to the shape of the molecule. After the reactions, enzymes are not changed, therefore making them reusable. The only reason that an enzyme would not be reusable would be if it goes through