Enzyme Inhibitors
Enzyme inhibitors interact with the enzyme and prevent it from working properly. There are two types of enzyme inhibitors, competitive and non-competitive. The ways in which inhibitors effect enzymes, as you might have guessed, centered around the active site of the enzyme.Inhibitors occur both naturally in the body (and are involved in regulating certain processes) and can be synthetically created too. Inhibitors are commonly used as drugs, as blocking enzyme activity can help remedy certain chemical imbalances or can be used to kill pathogens.
Competitive Inhibitors
These inhibitors compete with the substrate for the enzyme's active site. A competitive inhibitor will bind to a complementary active site of an enzyme, just like the substrate otherwise would, but will not react and will effectively block any substrates from binding to the enzyme. Their effects are usually temporary, after they have bound to the enzyme, they will unbind and the enzyme will be free to bind to the substrate again afterwards.
Non-Competitive Inhibitors
Rather than binding to the active site of an enzyme, non-competitive inhibitors bind to another part of the enzyme (called the allosteric site). This causes the shape of the active site to change, so the substrate shape is no longer complementary. Their effects are usually permanent- the enzyme, even after the inhibitor has left it, will still not function as it is effectively denatured.
Comparisons
Consider this: A scientist is measuring the rate of reaction of a mixture of competitive inhibitors, enzymes, and complementary substrates. What happens when he increases the concentration of substrates?
Now consider the same experiment, but replace the competitive inhibitors with non-competitive ones.
Because competitive inhibitors and substrates compete for the active site, increasing the amount of substrate compared to the amount of competitive inhibitor will mean that substrates are far more likely to bind to the enzyme before the inhibitor can. Imagine you're in a room with 50 other people and some famous guy you want to shake hands with. The problem is the other people want his autograph. Its pretty damn likely those other people are going to get to react with this famous guy before you can bind to him and stop him doing anything useful. But imagine if there were just 5 other people. Your job would be much easier. This is basically simple collision theory stuff from GCSE.
Now imagine there are 10 famous guys, 1,000,000 other people and 10 of you. But what if you happen to have glue all over yourself and want to give him a great big hug rather than a hand shake? You have (conveniently) transformed into the human equivalent of a non-competitive inhibitor. "So what?" I hear you say, "If you increase the concentration of substrates then the rate of reaction will increase until the effect of the inhibitor is negligible, right?". Wrong. When working with non-competitive inhibitors, the rate of reaction will actually level off at a considerably lower rate than it would if there were no inhibitors at all. Why? In order to give the famous guy your hug, you don't have to compete for his active site (his hands I guess), so you can waltz right past everyone and stick to him all you want. You then prevent him signing further autographs, and can move on to the next famous guy you want to cover in glue. Essentially, Non-Comp Inhibs don't compete with the substrate for the active site, and render the enzyme useless, so the overall rate of the reaction will always end up lower than it otherwise would no matter the concentration of substrate.
Here is a graph to make things even clearer! (seriously though, try and explain the shape of each line, why they level off where they do, etc...)
Non-Competitive Inhibitors
Rather than binding to the active site of an enzyme, non-competitive inhibitors bind to another part of the enzyme (called the allosteric site). This causes the shape of the active site to change, so the substrate shape is no longer complementary. Their effects are usually permanent- the enzyme, even after the inhibitor has left it, will still not function as it is effectively denatured.
Comparisons
Consider this: A scientist is measuring the rate of reaction of a mixture of competitive inhibitors, enzymes, and complementary substrates. What happens when he increases the concentration of substrates?
Now consider the same experiment, but replace the competitive inhibitors with non-competitive ones.
Because competitive inhibitors and substrates compete for the active site, increasing the amount of substrate compared to the amount of competitive inhibitor will mean that substrates are far more likely to bind to the enzyme before the inhibitor can. Imagine you're in a room with 50 other people and some famous guy you want to shake hands with. The problem is the other people want his autograph. Its pretty damn likely those other people are going to get to react with this famous guy before you can bind to him and stop him doing anything useful. But imagine if there were just 5 other people. Your job would be much easier. This is basically simple collision theory stuff from GCSE.
Now imagine there are 10 famous guys, 1,000,000 other people and 10 of you. But what if you happen to have glue all over yourself and want to give him a great big hug rather than a hand shake? You have (conveniently) transformed into the human equivalent of a non-competitive inhibitor. "So what?" I hear you say, "If you increase the concentration of substrates then the rate of reaction will increase until the effect of the inhibitor is negligible, right?". Wrong. When working with non-competitive inhibitors, the rate of reaction will actually level off at a considerably lower rate than it would if there were no inhibitors at all. Why? In order to give the famous guy your hug, you don't have to compete for his active site (his hands I guess), so you can waltz right past everyone and stick to him all you want. You then prevent him signing further autographs, and can move on to the next famous guy you want to cover in glue. Essentially, Non-Comp Inhibs don't compete with the substrate for the active site, and render the enzyme useless, so the overall rate of the reaction will always end up lower than it otherwise would no matter the concentration of substrate.
Here is a graph to make things even clearer! (seriously though, try and explain the shape of each line, why they level off where they do, etc...)
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| Source: https://teaching.ncl.ac.uk/bms/wiki/index.php/Enzyme |
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