What Is the Mechanism of Enzyme Activity?

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  • 0:04 What Is an Enzyme?
  • 1:13 How Do Enzymes Work?
  • 2:14 Lock & Key Model
  • 3:22 Metal Ion Catalysis
  • 4:51 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Have you ever wondered what an enzyme is and what it does? In this lesson, we'll learn what an enzyme is and how it does its job in the cell - the mechanism of enzyme activity. We'll also look at an example of an enzyme mechanism.

What Is an Enzyme?

Think of baking a delicious batch of cookies. Cookies can be a lot of work. You have to measure the flour and spend time rapidly mixing the butter and sugar with a wooden spoon. In fact, trying to beat together butter and sugar with a wooden spoon can take quite a bit of energy. However, most people have electric egg beaters or a fancy stand mixer to get the job done faster. These mixers act kind of like a tiny molecule called an enzyme inside our cells.

Enzymes are protein catalysts that speed up chemical reactions. Like the mixer sped up our beating of the butter and sugar, enzymes speed up things that have to happen inside the cell. And just like the cookies are still good if you use a mixer to make them more easily, the end product in a chemical reaction with an enzyme is still the same, we just got there more efficiently.

Instead of butter and sugar, enzymes work on starting materials called reactants and make them into end products. These are things the cell needs. For example, glucose may be converted to ATP and another molecule to make energy for the cell. Let's take a closer look at how enzymes accomplish this.

How Do Enzymes Work?

Enzymes speed up chemical reactions in the body, making things go faster than they normally would. But how do they accomplish this feat? Well, every reaction has an initial barrier called activation energy. Activation energy is like the hump the reaction has to get over before it can get started. Even reactions that net a production of energy still need to break this barrier. Think of it like pushing a car that broke down. It's really hard to get started, but once you and your friends get some momentum going, the car starts to roll and you can ease it to the side of the road.

Enzymes lower the activation energy of a reaction, which helps it go faster. Some enzymes, like carbonic anhydrase, which converts carbon dioxide to bicarbonate in the blood, make the reaction proceed nearly a million times faster than without the enzyme just by lowering activation energy. How does the enzyme do this? The answer is in the way the enzyme binds the reactants it works with, called the substrate.

Lock & Key Model

Enzymes and substrates are thought to bind together in a model called lock and key. In this model, the enzyme is considered the lock and the right key, or the substrate, fits in it perfectly. Each enzyme is specific to only one or two substrates, giving the enzyme specificity. When the enzyme binds the substrate there is a slight change in the shape of the enzyme. It shifts slightly to fit with the substrate better. This is called induced fit and is thought of as an extension to the earlier lock and key model. The lock and key not only fit together, but need each other to achieve the final goal.

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