Non-Competitive Inhibition: Examples & Graph

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  • 0:00 Enzymes And Enzyme Function
  • 1:18 Non-Competitive Inhibition
  • 2:07 Graphing Enzyme Activity
  • 3:28 Non-Competitive Graphing
  • 4:37 Non-Competitive…
  • 6:16 Lesson Summary
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Lesson Transcript
Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

This lesson will give a quick review of enzymes and enzyme function. The lesson will then briefly discuss non-competitive inhibition. It will explain how enzyme activity can be graphed with a focus on how the graph changes with non competitive inhibition. The lesson will also give examples of non-competitive inhibition.

Enzymes And Enzyme Function

A piece of bread left alone outside will, after a while, degrade and become part of the soil. If you eat the piece of bread, it will be broken down faster than if left alone. In eating the bread, you are acting as an enzyme. An enzyme speeds up chemical reactions that take place in a cell. Enzymes take substrates, like bread, and turn them into products, like the soil.

The area that enzymes bind substrates to is called the active site. When you eat a piece of bread, you chew it up in your mouth. Your mouth is akin to the active site where the chemical changes are taking place.

Many cellular functions rely on enzymatic activity. Therefore, it is important to regulate enzyme function. An out-of-control enzyme might form too many products that can adversely affect cellular function. If you continuously make brownies you will be left with no ingredients in your house for other desserts, and will have too many brownies to eat alone.

One way the cell can regulate enzyme function is through inhibition. By preventing the enzyme from turning substrate into product, cells can prevent a situation where there are too many products.

Non-Competitive Inhibition

There are three main types of cellular inhibition: competitive, uncompetitive, and non-competitive. Since this lesson focuses on non-competitive inhibition, only non-competitive inhibition will be discussed.

Non-competitive inhibition is where an inhibitor binds an area other than the active site and changes the active site so that it can't bind substrates. Let's say you, substrate, were trapped with a hungry lion, an enzyme. If a lion tamer jumps on the lion's back and muzzles the lion to prevent it from eating you, the lion-tamer would be acting as a non-competitive inhibitor. The muzzle represents a change in the active site; the lion can't open its mouth to eat you. The enzyme's active site is altered so it can't bind substrate anymore.

Graphing Enzyme Activity

Enzyme function can be measured by looking at the substrate concentration, or the amount of substrate available, and how fast it is being changed into product. A Michaelis-Menten Plot can be made by plotting substrate concentration on the x-axis verses rate of product formation on the y-axis.

For example, a fisherman uses his hands, the enzyme, to bait a hook and can use 1 piece of bait, the substrate, to catch 1 fish, the product, in 4 minutes. The rate of product formation is 1 fish every 4 minutes. If 10 fishermen are on the docks, the number of fish caught will depend on the amount of bait available. If there are only 3 pieces of bait and 10 fishermen, the rate is only 3 fish every 4 minutes. By increasing the substrate concentration, we can increase the amount of product. With 10 pieces of bait we can catch 10 fish every 4 minutes.

Since there are only 10 fishermen the max amount of fish in 4 minutes is 10. At this point the enzymes are saturated. That is, all binding sites are full, all hands have bait. The maximum rate of fish production, represented by letter V, then is 10 fish every 4 minutes. This is known as Vmax, or maximum velocity.

Non-Competitive Graphing

Now, suppose we start handcuffing the fishermen. The hands themselves are not changed, but now the position, or conformation, of the hands is different, making them unable to pick up the bait. This is non-competitive inhibition. If 2 of the 10 fishermen are handcuffed, the maximum rate of fish production changes from 10 fish every 4 minutes to 8 fish every 4 minutes, even if you add more bait. Non-competitive inhibition then, decreases, or lowers, the Vmax and is unaffected by an increase in substrate concentration.

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