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Allosteric Regulation & Feedback Inhibition of Enzymes

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  • 0:00 Enzyme Regulation
  • 1:20 Allosteric Regulation
  • 2:49 Feedback Inhibition
  • 5:17 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Like miniature factories, our cells are always working, and they want to avoid producing too much or too little. The solution is in enzyme regulation. In this lesson we will explore one type of enzyme regulation, and see exactly how this works.

Enzyme Regulation

Imagine you are running a factory. What sort of things do you have to consider? You've got to make sure your machines work and create a product. You also want to make sure that you are producing the right amount. If you make too much, you're wasting resources. If you make too little, well that's just poor business skills.

Our cells are a lot like little factories. Resources come in, cells grow and divide, genetic material is reproduced—it's truly an industrial process. Now, to create a product, a factory needs machinery and so does the cell. This is an enzyme, a protein responsible for speeding up chemical reactions. Basically, complex molecules called substrates enter the cell, and enzymes break substrates down into smaller products that can be processed into energy or something else. But, like any other factory, the cell needs to make sure that production stays high enough to meet demand but low enough so as to avoid wasting resources. So, it has its own systems of enzyme regulation to control the productivity of enzymes and keep the cell running like a well-oiled machine.

Allosteric Regulation

So, we've got our enzyme, our little factory machine here that's speeding up chemical reactions and pumping out products. But, what if we need to change its pace? Say that the cell needs to save some energy and cut down production; how do we do that?

Well, you may notice that there are a few parts to this machine. This big opening here, that's called the active site, it's where the substrate binds with the enzyme to be processed. That's where enzyme function really occurs. But over here on this other side, we've got another slot. This is the allosteric site, where molecules can bind with the enzyme to change its shape and function. We call the control of enzyme productivity by binding a molecule to the allosteric site allosteric regulation.

Here's how it works. This specific enzyme can only process substrates that are a certain shape. The substrate comes in, binds to the active site, is turned into smaller products…bing bang boom. But, what happens when we bind another molecule with the allosteric site. The shape of the active site changes, and now the substrate won't fit. In this case, we used allosteric regulation to stop production, although this process can also be used to simply slow down enzyme function, or even to speed it up.

Feedback Inhibition

There are different ways that allosteric regulation can occur, but one of the most common involves the process of feedback inhibition, in which the final product of a series of reactions binds with the first enzyme to stop production. Here's how this works. Look at this assembly line. We've got a series of enzymes performing different chemical reactions to break apart a large substrate, and at the very end we have our basic products.

Now, the cell only needs so much product, and once we've accumulated too much, an alarm goes off, prompting the allosteric reaction of feedback inhibition. After all, there's no need to keeping wasting energy if we have enough product. So, how do we shut down the system? The very first enzyme in this chain has an allosteric site that is shaped to only bind with the final product. This means that this enzyme won't stop until there is enough surplus for an extra product to make its way over and bind with the allosteric site, but once it does, the entire assembly line shuts down, and the cell conserves energy.

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