A drug that binds to the active site of an enzyme and prevents substrate binding is known as a ________.

A drug that binds to the active site of an enzyme and prevents substrate binding is identified as a competitive inhibitor. Competitive inhibitors directly compete with the substrate for binding to the active site of the enzyme. When a competitive inhibitor occupies the active site, it effectively blocks the substrate from binding, thereby inhibiting the enzyme's activity.

The key feature of competitive inhibition is that the inhibitor resembles the substrate in structure, allowing it to fit into the active site of the enzyme. This process can be overcome by increasing the concentration of the substrate, which allows more substrate molecules to bind to the enzyme instead of the inhibitor, thus restoring enzyme activity.

Other options, such as non-competitive inhibitors and allosteric inhibitors, act through different mechanisms. Non-competitive inhibitors bind to an enzyme at a site other than the active site and can inhibit the enzyme regardless of whether the substrate is bound. Allosteric inhibitors similarly bind to sites other than the active site but can induce a conformational change in the enzyme that reduces its activity. Meanwhile, a substrate mimic would resemble the substrate but does not necessarily imply inhibition. This specificity in action defines competitive inhibitors clearly in relation to substrate binding.