Enzyme Regulation: Feedback Control - Online Tutor, Practice Problems & Exam Prep

A metabolic pathway consists of a series of biochemical reactions within a cell, regulated by feedback control. The end product acts as a negative allosteric regulator, binding to the allosteric site of the enzyme, rendering it inactive. This prevents further production of the end product when sufficient levels are reached. The process involves the enzyme's active site binding to a substrate, forming an enzyme-substrate complex, and ultimately producing the final product. Once the end product decreases, it detaches, allowing the pathway to reactivate, illustrating the dynamic nature of enzyme regulation.

Feedback Control Concept 1

Now, a metabolic pathway is a series of biochemical reactions taking place within a cell. We're going to say that under feedback control, the end product of a pathway acts as an on-off switch for the enzyme in the first step. The end product is a negative allosteric regulator of the enzyme in the first step. So let's take a look at this image, and let's just ignore this first one for right now. We'll come back to it. Now, let's say we're starting out with this first portion here. This enzyme has an active site, and here, 'a' represents our substrate. It also has this allosteric site here. Right now, there's no regulator in sight to attach to it, so the active site is going to be unaffected. The substrate is free to come and attach to this enzyme, so we’d say that this is an active enzyme. Once the substrate attaches to the enzyme, we get our enzyme-substrate complex, which is here. This helps to create our intermediates. So it would help to create structure 'b,' which would eventually create intermediate 'c,' so that we can finally get to our product 'd.' So we've reached our product 'd' here. The whole point of this reaction is to help to make this product 'd.' And once we’ve reached an efficient number or a suitable amount of it, we no longer need to continue making it. So what happens is that this product 'd' here, this end product will come back and attach to the allosteric site of our enzyme. By attaching to the allosteric site of our enzyme, it's going to act as a negative allosteric regulator. It is going to basically change the active site enough that the substrate can no longer bind to it. So, we have, in essence, created an inactive enzyme. The substrate no longer fits in the active site, so the enzyme cannot be utilized. This will help us from continuing to make more of our end product 'd.' Now, once that amount deteriorates and goes down again, we could have this end product 'd' unattach itself from the allosteric site and begin the whole process again, right? So, this is what we talk about in our feedback control. We have our enzyme binding to the substrate to make our final product, our end product 'd.' Once we've made enough of it, some of it will come and attach to the enzyme, deactivating it or making that enzyme inactive. So, we stop making it. So this is the whole idea of enzyme regulation in terms of feedback control.

Feedback Control Example 1

Which of the following statements cannot be true about feedback control?

Regulation is achieved by negative allosteric control of an enzyme in the first step. This is true. The end product that we make at the end, some of it will come and attach to the enzyme. It'll attach to the allosteric site, thereby altering the size of the active site so that the substrate can no longer attach. This is negative allosteric regulation, so this is true. The end product affects its own production. Yes, if you're making more than enough of the product and you no longer want to make more, then it could come and attach to the allosteric side of the enzyme and basically deactivate or make that enzyme inactive. So in that way, it is controlling how much of it is being made.

The end product binds irreversibly to the enzyme in the first step. No, it's not irreversible. It is reversible. The end product will attach to the allosteric site and make that enzyme inactive, so it will no longer continue making the product. But, eventually, let’s say you consume all of that product and you want to start making it again. The end product will detach from the allosteric side of the enzyme, and thereby reactivate it so that it can continue to make more product. It's a way of controlling the amount of your end product being formed. When you have too much of it, an overabundance of it, you turn off the enzyme. When you have a low amount of it, you turn the enzyme back on. And this has to do with attaching and detaching to the allosteric side of the enzyme. So here, this is not true. It's not irreversible.

Feedback control can help to save the energy of the cell by shutting down an entire pathway. Yes, it costs a lot of energy to help to make these products. And if you have a ton of a product, what's the point of continuing this series of reactions? You already have enough, so it's good to shut it down until you need some more. So, yes, this would help to save the energy.

So, the only statement here that is not true about feedback control will be option c.

Is the following diagram a correct illustration of feedback control?

• A. Yes
• B. No

Here’s what students ask on this topic:

What is feedback control in enzyme regulation?

Feedback control in enzyme regulation is a mechanism where the end product of a metabolic pathway acts as a regulator for the pathway. Specifically, the end product binds to the allosteric site of the enzyme involved in the first step of the pathway, acting as a negative allosteric regulator. This binding changes the enzyme's active site, preventing the substrate from binding and thus rendering the enzyme inactive. This stops further production of the end product when sufficient levels are reached. Once the end product levels decrease, it detaches from the enzyme, allowing the pathway to reactivate.

How does the end product act as a negative allosteric regulator in feedback control?

In feedback control, the end product of a metabolic pathway acts as a negative allosteric regulator by binding to the allosteric site of the enzyme involved in the first step of the pathway. This binding induces a conformational change in the enzyme, altering its active site so that the substrate can no longer bind to it. As a result, the enzyme becomes inactive, preventing further production of the end product. This regulation ensures that the cell does not produce an excess of the end product, maintaining metabolic balance.

What happens to the enzyme when the end product binds to its allosteric site?

When the end product binds to the allosteric site of the enzyme, it induces a conformational change in the enzyme's structure. This change alters the shape of the enzyme's active site, making it unable to bind to its substrate. As a result, the enzyme becomes inactive, and the metabolic pathway is halted. This prevents the overproduction of the end product. Once the levels of the end product decrease, it detaches from the allosteric site, allowing the enzyme to return to its active form and the pathway to resume.

Why is feedback control important in metabolic pathways?

Feedback control is crucial in metabolic pathways because it helps maintain homeostasis within the cell. By regulating the activity of enzymes through the end product acting as a negative allosteric regulator, the cell can prevent the overproduction of certain compounds. This ensures that resources are not wasted and that the cell's metabolic balance is maintained. Feedback control allows the cell to respond dynamically to changes in the concentration of end products, ensuring efficient and balanced metabolic processes.

What is the role of the allosteric site in enzyme regulation?

The allosteric site is a specific region on an enzyme where regulatory molecules, such as the end product of a metabolic pathway, can bind. When a molecule binds to the allosteric site, it induces a conformational change in the enzyme's structure. This change can either activate or inhibit the enzyme's activity. In the context of feedback control, the binding of the end product to the allosteric site acts as a negative allosteric regulator, altering the active site and rendering the enzyme inactive. This prevents further production of the end product, maintaining metabolic balance.