Enzyme Inhibition: Videos & Practice Problems

Enzyme inhibition is crucial for regulating chemical reactions in cells. There are two main types of inhibitors: competitive and noncompetitive. Competitive inhibitors bind to the active site of an enzyme, blocking substrate access, while noncompetitive inhibitors attach to an allosteric site, altering the enzyme's shape and preventing substrate binding. This regulation is essential for maintaining metabolic balance and can be influenced by factors like substrate concentration and enzyme affinity. Understanding these mechanisms is vital for applications in biochemistry and pharmacology.

Enzyme Inhibition

In this video, we're going to introduce enzyme inhibition. Recall that enzymes are all about speeding up chemical reactions. But sometimes, the reactions might be going too fast, and the cell might need to stop the enzyme from going so fast. In that case, enzyme inhibition can be useful. Enzyme inhibitors are defined as compounds that interfere with and selectively inhibit the catalysis of specific enzymes. Enzyme inhibitors can be used to slow down enzymes if they're going too fast. Now really, there are two types of inhibitors that we're going to introduce here in this video, and those two types are listed down below.

The first type is competitive inhibitors, and the second type that we're going to introduce are non-competitive inhibitors. Competitive inhibitors, as their name implies with the competitive part, are going to compete with the substrate for a position in the free enzyme's active site. Competitive inhibitors can only bind to the enzyme and compete with each other for a binding spot in the active site of the enzyme. Let's take a look at our image down below over here on the left-hand side at competitive inhibition. Notice that the enzyme once again is shown in red, and in blue what we're showing you is the competitive inhibitor. It's called a competitive inhibitor because it's going to compete with the substrate, which is in black, for a position in the enzyme's active site. If the competitive inhibitor binds to the enzyme's active site before the substrate does, then the competitive inhibitor is going to block the substrate from binding to the active site as we can see over here. Notice that the competitive inhibitor is binding to the active site of the enzyme and it binds to the active side of the enzyme, it is preventing the normal substrate from binding and if the normal substrate cannot bind, then that means that catalysis is going to be prevented, and the enzyme's reaction is going to essentially slow down and be inhibited.

The second type of inhibitor that we're going to talk about are non-competitive inhibitors. As their name implies, they are non-competitive, so they do not compete with the substrate for a position in the active site. Instead, the non-competitive inhibitor is going to bind to what's known as an allosteric site. The allosteric site on an enzyme is defined as an alternative site for an inhibitor binding that is not going to be the active site. Let's take a look at our image down below over here on the right-hand side to get a better understanding of non-competitive inhibition. Notice that the non-competitive inhibitor is shown here in purple, so we can go ahead and label it as the non-competitive inhibitor. The non-competitive inhibitor, notice, is not going to compete with the substrate over here for a binding position in the active site. Instead, the non-competitive inhibitor is going to bind to a completely different site over here that we have in blue, and this site is referred to as the allosteric site. When an inhibitor binds to the allosteric site of an enzyme, it can cause the enzyme to change its shape, to alter its shape. When it alters its shape, it's going to also alter the shape of the active site. Notice that the active site here is taking on a different shape than what it used to have before the non-competitive inhibitor bound. The active site will change in such a way that it will prevent the substrate from binding to the enzyme. If the substrate cannot bind to the enzyme, then that is going to prevent or inhibit catalysis and slow down the enzyme. These inhibitors can be used to slow down and inhibit enzymes.

This here concludes our introduction to enzyme inhibition as well as competitive and non-competitive inhibitors, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Which of the following statements correctly describes competitive inhibition?

• A. A competitive inhibitor binds to the substrate and inhibits it from binding to the active site of the enzyme.
• B. A competitive inhibitor binds to a site other than the active site and inhibits the substrate from binding.
• C. A competitive inhibitor binds to the active site and degrades the enzyme.
• D. A competitive inhibitor binds to the active site of an enzyme and inhibits the substrate to bind.

Answer: (D)

How does a noncompetitive inhibitor decrease the rate of an enzyme-catalyzed reaction?

• A. By binding to the active site of the enzyme, thus preventing binding of the normal substrate.
• B. By binding to an allosteric site, thus changing the shape of the active site of the enzyme.
• C. By decreasing the free-energy change of the reaction catalyzed by the enzyme.
• D. By binding to the substrate, thus changing its shape so that it no longer binds to the active site of the enzyme.

Answer: (B)

Which of the following types of enzyme inhibition is overcome by increasing the substrate concentration?

• A. The need for a coenzyme.
• B. Noncompetitive inhibition.
• C. Competitive inhibition.
• D. None of the above.

Answer: (C)

Here’s what students ask on this topic:

What is enzyme inhibition and why is it important?

Enzyme inhibition refers to the process by which the activity of an enzyme is decreased or stopped by a specific compound known as an inhibitor. This regulation is crucial for maintaining metabolic balance within cells. Enzyme inhibitors can slow down or halt reactions that are proceeding too quickly, ensuring that cellular processes occur at appropriate rates. This is essential for various biological functions, including metabolic pathways, signal transduction, and homeostasis. Additionally, enzyme inhibition has significant applications in medicine, such as in the design of drugs that target specific enzymes to treat diseases.

What are the differences between competitive and noncompetitive inhibitors?

Competitive inhibitors bind to the active site of an enzyme, directly competing with the substrate for access. This prevents the substrate from binding, thereby inhibiting the enzyme's activity. In contrast, noncompetitive inhibitors bind to an allosteric site, which is a different location on the enzyme. This binding causes a conformational change in the enzyme's structure, altering the shape of the active site and preventing the substrate from binding. While competitive inhibition can be overcome by increasing substrate concentration, noncompetitive inhibition cannot be reversed in this manner.

How do competitive inhibitors affect enzyme activity?

Competitive inhibitors affect enzyme activity by binding to the enzyme's active site, where the substrate would normally bind. This competition prevents the substrate from accessing the active site, thereby inhibiting the enzyme's catalytic function. As a result, the rate of the enzyme-catalyzed reaction decreases. However, this type of inhibition can be overcome by increasing the concentration of the substrate, which can outcompete the inhibitor for the active site.

What is an allosteric site and how does it relate to noncompetitive inhibition?

An allosteric site is a specific location on an enzyme that is distinct from the active site. Noncompetitive inhibitors bind to this allosteric site, causing a conformational change in the enzyme's structure. This change alters the shape of the active site, making it less effective or completely ineffective at binding the substrate. As a result, the enzyme's catalytic activity is inhibited. Unlike competitive inhibition, noncompetitive inhibition cannot be overcome by simply increasing the substrate concentration.

Why can't noncompetitive inhibition be overcome by increasing substrate concentration?

Noncompetitive inhibition cannot be overcome by increasing substrate concentration because the inhibitor binds to an allosteric site, not the active site. This binding induces a conformational change in the enzyme, altering the shape of the active site and preventing substrate binding. Since the inhibitor does not compete with the substrate for the same site, increasing the substrate concentration does not affect the inhibitor's ability to bind to the allosteric site and inhibit the enzyme's activity.