What is the term for the change in shape of the active site of an enzyme when the substrate enters?

The term that describes the change in shape of an enzyme's active site upon substrate binding is known as "induced fit." This concept suggests that the active site of the enzyme is not a rigid structure but rather flexible, allowing it to adapt to the shape of the substrate when it binds. This change enhances the enzyme's ability to catalyze the reaction, making it more effective at converting substrates into products.

When the substrate enters the active site, that slight change in shape increases the interactions between the enzyme and the substrate, lowering the activation energy required for the reaction to proceed. The induced fit model emphasizes the dynamic nature of enzyme-substrate interactions, contrasting with earlier models that depicted a more static lock-and-key fit between the enzyme and substrate.

The other terms, such as substrate binding and enzyme activation, describe different aspects of enzyme functionality but do not specifically refer to the conformational change that occurs during substrate binding. Competitive inhibition involves an inhibitor competing with the substrate for the active site, which is unrelated to the conformational changes discussed in the context of induced fit. Thus, "induced fit" is the most accurate term for this specific process.