Enzyme Regulation: Allosteric Control - Video Tutorials & Practice Problems
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concept
Allosteric Control Concept 1
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Enzyme regulation is a mechanism. Cells used to turn on or off enzymes as needed. And we're gonna say there's three types we have what's called allosteric control. We have feedback control. And then finally, we have what's called covalent modification. Now, let's look, take a look at allosteric control. Now, with allosteric control, it's achieved by allosteric enzymes that have two types of binding sites. Now, the active site, we know that's the spot for our substrate to come and attach to the enzyme. But now we have what's called an allosteric site. This is for what we call the regulator. Now, our regulator also called our factor. This binds to the Alistair site and it either opens or closes an active site. So here we take a look here at these two images. In both of them, we have our substrate which we abbreviate as s in the first image. Here we have this triangular green block and it's attaching to this portion right here. When it attaches there, it actually opens up and creates an active site on the enzyme for a substrate to attach. Now, we're gonna say a positive regulator, it helps to increase it increases the rate of reaction by making an active site available to the substrate. So this first image represents a positive allosteric regulator. By attaching to this allosteric site. It helps to open up an active site somewhere else on the enzyme for substrate to then come and attach to that site. In the other image, we have this regulator and it attaches to this allosteric site. Before it does this, we have an active site available for our substrate to attach. But after the regulator has attached, the active site disappears, there's no longer a place for the substrate to attach. This would represent a negative allosteric regulator. So a positive one increases the rate of reaction. So a negative one would decrease the rate of reaction. So here it decreases the rate of reaction by making an active site unavailable to substrate. So just remember, we have our active site which is where the substrate wants to attach. But then we have our regulator or e factor that can attach to the allosteric site somewhere else on the enzyme. And this will either help to free up, open up an active site or close it. This can help to either increase the rate of reaction by opening up an active site or decreasing the rate of reaction by closing up an active site. So keep this in mind that this represents allosteric control.
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example
Allosteric Control Example 1
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Which of the following statements is incorrect about allosteric enzymes. A the activity of an allosteric enzyme can be controlled by regulatory molecule. This is true. Remember, the regulatory molecule or a factor molecule can either help to increase or decrease the rate of the reaction by affecting the active site of the enzyme. So this is true. Allosteric enzymes have two types of binding sites. So this is also true. Remember, there's two ways in which we can affect the overall uh binding sites. We can have positive or negative. The binding of allosteric regulator to an enzyme can change the availability of an active site. Yes, a positive regulator can in um can increase the rate of reaction by opening up an active site. Whereas a negative one can close up on already present active site. As soon as it binds to the allosteric site, the overall shape of an allosteric enzyme always remains the same. No, once a regulatory molecule, a factor molecule attaches to the allosteric site, this can open up or close an active site. This would cause a change in the overall shape of the enzyme. So here option D is a statement that's incorrect about allosteric enzymes.
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Problem
Problem
Isoleucine can attach to the enzyme threonine deaminase and can decrease its activity. Isoleucine can be classified as:
A
Positive allosteric regulator
B
Negative allosteric regulator
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