What Goes On in the Cytoplasm

Thousands and thousands of different chemical reactions take place in the cytoplasm.

Here's an example of a very generic chemical reaction:

In the above reaction, molecules X and Y are the reactants and molecule Z is the product. However, the reaction won't happen unless X and Y get together.

X and Y need a mutual "friend" that will help them get together in the same place at the same time so they can react and form Z. The mutual friend is an enzyme. Here's a picture of an enzyme that would work nicely to get X and Y together.

We'll call the enzyme molecule E. If E is around, the reaction between X and Y occurs much more quickly than if E is not around. We call E a catalyst. Catalysts simply make chemical reactions occur faster. E's job is to catalyse the reaction between X and Y.

Notice that the spaces on the top of molecule E match up with molecule X's shape. The spaces on the bottom match up with molecule Y's shape.

So if molecule E is floating around in the cytoplasm of a cell, X and Y have a good chance of getting together. Once they do, they react to form molecule Z.

When the reaction is finished, molecule E is still around, and is unchanged. It's now free to go and find another pair of X and Y to catalyse another reaction between them. So here's the first important fact to remember about an enzyme:

When an enzyme catalyses a reaction, it is not used up in the reaction.