The part of an enzyme that has a specific shape to fit with the substrate is called the active site.

Here's why this is important:

* Lock and Key Model: The active site acts like a lock, and the substrate acts like a key. The specific shape of the active site allows only the correct substrate to bind to it.

* Specificity: This specificity is what makes enzymes so efficient. They can catalyze a particular reaction without affecting other molecules in the cell.

* Induced Fit: While the lock and key model is a good starting point, the active site can actually change shape slightly to better fit the substrate once it binds. This is called induced fit.

Let me know if you have any other questions about enzymes!