How do enzymes lower the activation energy of a reaction?

Enzymes facilitate chemical reactions by lowering the activation energy required for the reaction to proceed. They accomplish this by providing an alternative reaction pathway that requires less energy than the uncatalyzed reaction. This alternative pathway usually involves the formation of a transient enzyme-substrate complex, which stabilizes the transition state and makes it easier for the reactants to convert into products.

When enzymes bind to their substrates, they can induce strain in the substrate or bring reactive groups into closer proximity, thereby lowering the energy barrier that must be overcome for the reaction to occur. This effect not only accelerates the rate of the reaction but also allows physiological reactions to occur under the mild conditions typically found within living organisms.

In contrast, the other options, such as altering temperature, increasing reactant concentration, or changing pressure, pertain to different factors that can influence reaction rates but do not describe the mechanism by which enzymes lower activation energy.