Questions: Choose the best description of how a substrate binds to an enzyme active site. A. The substrate bonds covalently to the active site. B. The substrate binds to the active site if its geometry and shape fit the geometry of the active site. C. The substrate binds to the active site if there are strong enough intermolecular forces attracting the substrate to the active site. D. The substrate binds to the active site if the geometry fits and there are sufficient intermolecular forces attracting the substrate to the active site.

The answer is D: The substrate binds to the active site if the geometry fits and there are sufficient intermolecular forces attracting the substrate to the active site.

Explanation for each option:

A. The substrate bonds covalently to the active site.
This is incorrect. Substrates typically bind to enzyme active sites through non-covalent interactions such as hydrogen bonds, ionic interactions, and van der Waals forces, rather than covalent bonds.

B. The substrate binds to the active site if its geometry and shape fit the geometry of the active site.
This is partially correct. While the geometric fit is important (often described by the "lock and key" model or the "induced fit" model), it is not the only factor. Intermolecular forces also play a crucial role in binding.

C. The substrate binds to the active site if there are strong enough intermolecular forces attracting the substrate to the active site.
This is also partially correct. Intermolecular forces are important for binding, but the geometric fit is equally crucial for the substrate to bind effectively.

D. The substrate binds to the active site if the geometry fits and there are sufficient intermolecular forces attracting the substrate to the active site.
This is the most comprehensive and correct description. Both the geometric fit and the presence of sufficient intermolecular forces are necessary for effective binding of the substrate to the enzyme's active site.