An enzyme is a type of protein that acts as a biological catalyst, facilitating and accelerating chemical reactions within living organisms. Enzymes are essential for virtually all biochemical processes that occur in cells, as they enable these processes to occur at biologically relevant speeds and conditions.
Enzymes work by lowering the activation energy required for a chemical reaction to take place. Activation energy is the energy barrier that must be overcome for reactant molecules to transform into products. Enzymes achieve this by providing a specific microenvironment that promotes the interaction of reactant molecules and the formation of transition states, which are intermediate stages during a reaction.
Enzymes are highly specific in their actions. Each enzyme is designed to catalyze a particular chemical reaction or a group of closely related reactions. This specificity arises from the enzyme's unique three-dimensional structure, which includes an active site—a region where the reactant molecules, called substrates, bind and undergo the catalytic process.
Enzymes are not consumed or changed during the reactions they catalyze. Instead, they facilitate reactions by temporarily forming enzyme-substrate complexes. Once the reaction is complete, the products are released from the active site, and the enzyme is free to catalyze additional reactions.
Enzymes are crucial for life because they enable biochemical processes to occur efficiently within the narrow range of conditions found in living organisms. Without enzymes, many of these reactions would be too slow to sustain life or would require conditions that are incompatible with the delicate balance of a living system.