Enzyme

En-zyme means "in yeast", so called because that is where these proteins were first found. Enzymes are needed to do many different jobs: breaking down food to get energy; building small molecules up into larger ones; rearranging molecules; getting rid of waste products.

For every job which has to be done in life there is at least one kind of enzyme. Sometimes several of them work together to achieve a single task. Let's follow a simplified example.

Enzyme breaks target

Suppose a cell needs to split a food molecule in two. The first step is that, because the surrounding water molecules are constantly moving, they carry the target into the enzyme.

Water carries the target into the enzyme

Obviously the enzyme must not split just any molecule. If it did it might attack the living cell it belongs to and kill it. So the enzyme must be able to identify its target molecule. The enzyme has a hole with just the right shape to capture the target.

The target fits like a key into a lock

As a result of the target entering, the enzyme changes shape and breaks the target in two.

The enzyme breaks the target

Once the target is broken, the enzyme changes shape again and releases the broken fragments.

The enzyme releases the fragments, ready for the next target to enter

An enzyme can do only one job - in this case breaking a food molecule - but it can do that job many times. Notice that the shape of the crack in this enzyme is important. The shape decides which molecule the enzyme can do work on and what job can be done on it. Life has to use many different enzymes, one for each job it needs to do, each one with a different shape.

Size of an enzyme

On Soccearth (a soccer ball blown up to the size of the Earth) a typical enzyme would be 20 to 40 cm across, about the size of a microwave oven.