Question

What is the difference between a competitive and a non-competitive inhibitor of an enzyme? Which type of inhibition can be overcome by increasing the substrate concentration? Why?

Answer 1

Competitive inhibitors bind to the active site of the enzyme and compete with the substrate, while noncompetitive inhibitors bind to a different site and do not directly compete with the substrate. Competitive inhibition can be overcome by increasing the substrate concentration.

Step-by-step explanation:

Competitive inhibition is when an inhibitor reversibly binds to an enzyme at the enzyme active site; competing with the substrate for binding. A competitive inhibitor must be a molecule that is structurally similar to the substrate molecule, allowing it to interact with the enzyme active site through similar non-covalent interactions, but it does not, or cannot, undergo the same chemical reaction. When the inhibitor is bound to the active site, it blocks the correct substrate from binding and catalysis from occurring. However, as a reversible inhibitor, it can disassociate from the enzyme eventually allowing for the correct substrate to bind and the catalysis to occur. Because the inhibitor and substrate are in competition for the same active site, inhibition is concentration-dependent. As shown in the below plot of rate of reaction vs. substrate concentration (Figure 19.6.1), the competitive inhibitor slows the rate of reaction, but at higher substrate concentrations, the normal maximum rate can be reached.

A noncompetitive inhibitor can bind to either the free enzyme or the enzyme-substrate complex because its binding site on the enzyme is distinct from the active site. Binding of this kind of inhibitor alters the three-dimensional conformation of the enzyme, changing the configuration of the active site with one of two results. Either the enzyme-substrate complex does not form at its normal rate, or, once formed, it does not yield products at the normal rate (see Figure 19.6.1). Because the inhibitor does not structurally resemble the substrate, nor is it competing with the substrate for the active site, the addition of excess substrate does not reverse the inhibitory effect.

So, in summary, the difference between competitive and noncompetitive inhibitors is that competitive inhibitors bind to the active site of the enzyme and compete with the substrate, while noncompetitive inhibitors bind to a different site and do not compete directly with the substrate. Competitive inhibition can be overcome by increasing the substrate concentration because the higher concentration of substrate allows for more substrate molecules to outcompete the inhibitor and bind to the active site, leading to the normal maximum rate of enzymatic reaction.

Answer 2

Competitive inhibitors compete with the substrate to enter the active site of the enzymes thanks to their chemical affinity with them, thus blocking the enzyme's action with the original substrate.

Non-competitive inhibitors do not interact directly with the active site of the enzymes, but adhere to them by other sites, changing their structure and thus decreasing their affinity for the original substrate, blocking their functioning.

Competitive inhibition can be overcome by increasing the substrate concentration because the probability that the enzyme interacts with the inhibitor molecules will be lower, and the expected reaction will take place.

Step-by-step explanation:

Non-competitive inhibition cannot be overcome by increasing the concentration of the substrate because the inhibitor, by interacting with the enzyme and changing its structural configuration, will prevent the enzyme from succeeding in inserting the substrate into its active site, also preventing the chemical reaction.