Enzymes speed up the reaction rate of a substrate by lowering the activation energy of the reaction. This is done by providing an alternative pathway for the reaction to take place, which requires less energy. Enzymes bind to the substrate and form an enzyme-substrate complex, which then undergoes a series of steps to convert the substrate into the product. The enzyme-substrate complex lowers the activation energy of the reaction by stabilizing the transition state, which is the highest energy point along the reaction pathway. This allows the reaction to take place more quickly and efficiently.

Additionally, enzymes can also increase the rate of reaction by increasing the effective concentration of the substrate. This is achieved by binding to the substrate and holding it in close proximity to the active site, which is the part of the enzyme that catalyzes the reaction. By increasing the concentration of the substrate, the enzyme increases the likelihood of the substrate colliding with the active site and undergoing a reaction.

Overall, enzymes speed up the reaction of a substrate by lowering the activation energy and increasing the effective concentration of the substrate. These effects allow the reaction to take place more quickly and efficiently, leading to increased reaction rates.