ENZYMES
Enzymes Enzymes are protein catalysts A catalyst is a substance that speeds up a chemical reaction without being used up in the process Rates of chemical reactions could be increased with the addition of heat, however heat may denature proteins A catalyst can speed up the rate of chemical reactions at moderate temperature decreasing risk of denaturation
Enzymes The substrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction Enzymes are very specific for the substrate to which they bind Name of enzymes ally end in –ase (ex. lactase, polymerase, maltase, etc.)
How Do Enzymes Work? In an enzyme-catalyzed reaction, the substrate binds to a very small portion of the enzyme The location where the substrate binds is called the active site The substrate must fit into a pocket or groove of the 3D structure of the protein Once the substrate binds to the enzyme, the structure is called the enzyme/substrate complex
Induced-Fit Model As the substrate enters the active site, its functional groups come close to the functional groups of a number of amino acids in the enzyme This causes the enzyme to change shape slightly to accommodate the substrate This slight change in shape causes the substrate to become “stressed” (distorting a particular bond) and, therefore, lowers the activation energy needed to break the bonds
When the bonds are broken the conformation of the substrate changes and the enzyme loses its affinity for the products releasing them back into the environment The active site now becomes available for another substrate to attach The recycling of enzyme molecules causes cells to catalyze many reactions with relatively small numbers of enzymes
Co-factors & Co-enzymes Some enzymes require additional assistance to function These co-factors and co-enzymes are not proteins Co-factors: Inorganic metal ions such as Zn2+ and Mn2+ They help draw out electrons from the substrate where bonds need to be broken
Co-enzymes Organic Shuttle molecules from one enzyme to another Examples: NAD+ and FAD+ These usually get reduced to harvest energy Act as electron carriers