Enzymes are biological catalysts that speed up chemical reactions in the bodies of living organsms. Enzymes are proteins made up of long chains of amino acids, the chains of amno acids are different in each protein which means that different types of enzymes are different shapes. The shape of an enzyme affects how they work.
To speed up chemical reactions using enzymes the molecule must fit into the active site of the enzyme (this can be explained by using the lock and key model).
Enzymes have an active site which only the correct molecule fits into, when the molecule is in the active site a reaction takes place and the product leaves the active site and the enzyme can be used for a reaction like this again.
Without enzymes the body would have to be a lot hotter for chemical reactions to take place fast enough to keep you alive, this would mean that you would have to eat a lot more food to get enough energy. But if the body was any hotter body cells would get damaged.
Enzymes and High Temperatures
Higher temperatures speed up reactions because they give the atoms more energy which gives them more energy which makes them move quicker. This means that the molecules collide more often and with more energy which makes the rate of reaction speed up.
However, high temperatures can change the shape of an enzyme so that the molecules can no longer fit into it. These enzymes are denatured.
The optimum temperature of an enzyme is the temperature that it works best at. The optimum temperature of enzymes in humans is 37 degrees celcius.
The optimum pH of an enzyme is the pH at whch it works best. Different enzymes have different optimum pH's.