Enzymes are biological catalysts that increase the rate of biochemical reactions by lowering the energy of activation. They are typically proteins that bind specifically to substrates and induce a shape change that facilitates the chemical reaction. This induced fit allows the enzyme to reduce the energy needed for the reaction to occur and be used repeatedly without being consumed in the process. Changing conditions like temperature, pH, substrate concentration, or adding inhibitors can impact the reaction rate by altering how well the enzyme and substrate interact.