What are proteins?

Let's summarize where we've got to so far:

• Living things are made of cells
• Cells are made of various different things and we get most of those by eating other animals and plants
• We've seen what cells look like
• Two of the most important components of cells are proteins and DNA

So we've heard that proteins are important, but what are they and why are they important?

Well first of all, let's see some protein. If you get an egg and crack it open, take a look at the egg white. Egg white is an almost pure solution of protein in water (85% water, 10% protein). It contains mostly four proteins called ovalbumin (54% of the protein), conalbumin (12%), ovamucoid (11%) and lysozyme (3.4%), but also small amounts of some other proteins (avidin, ovoglobulin, ovinhibitor and flavoproteins) as well as some vitamins and minerals.

We'll look at a picture of what ovalubumin looks like at the atomic level a bit later

OK, we've seen some protein, but what does it do? Why is it so important??

Proteins can do lots of things.:

• They can be structural (the inside of your eye is largely a protein solution)
• They can pass messages around the body
• They can be used to store things and to transport them around the body (for example, haemaglobin is a protein in your red blood cells which transports oxygen)
• They can help kill invading organisms (antibodies are part of the immune system and the lysozyme protein in egg white helps kill bacteria)

One of the most important things they do is act as enzymes. Enzymes are catalysts: they help chemical reactions to occur.

On the Next Page we will see some enzymes in action.