Why are enzymes important to the function of a cell??

Question

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Answer 1

Enzymes are biomolecules (usually proteins) that CATALYZE (i.e. increase the rate of) CHEMICAL REACTIONS. Each of the many enzymes typically works with only one or a small set of chemicals, called SUBSTRATES.  The enzyme converts substrates into different molecules, called the PRODUCTS.  Almost all processes in a biological cell need enzymes in order to occur at significant rates. Since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.

Like all catalysts, enzymes work by lowering the ACTIVATION ENERGY (Ea or ΔG‡) for a reaction, thus dramatically increasing the rate of the reaction.  Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions.  

Enzyme activity can be affected by other molecules. INHIBITORS are molecules that decrease enzyme activity; ACTIVATORS are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g. pH), and the concentration of substrate.