Proteins, it is fair to say, are the big molecules that actually do all the work in your body. The only work that they don't directly do is hold you up, your skeleton is bone, which contains some protein, but it is the mineral part that provide the rigidity for your shape, the proteins make sure it is the right shape for you and the demands that you are putting on it, and provide it with its strength. It is certainly proteins in your muscles that let you move, proteins that chop your food up so you can digest it and proteins that carry most of the food across your guts so it can enter your body.
Proteins
are made up of chains of amino acids, and are often folded up into a
ball shape. The picture to the right shows a typical protein folded up.
There are 20 different sorts of amino acid, each with slightly different
properties, and these are often grouped together which is why some of
the 'balls' in this image, each of which represents a different amino
acid in the chain, are coloured, so that you can quickly see the amino
acids with similar properties.
Since we know that there are 20 different amino acids, you can work out roughly how many different sorts of protein there could be.
If you have one amino acid, there are obviously twenty possibilities. If you have two joined together, there are 20 X 20 = 400 possibilities. You might, if you are clever enough, say that some of these are duplicates. For example, a dipeptide (two amino acids joined together) consisting of Glycine-Valine might be the same as Valine-Glycine. It is the same two amino acids, just in a different order. However, amino acids clip together a bit like beads. If you have a yellow bead for glycine and green bead for valine, and clip them together, the two different sets are similar, but have a different coloured nub sticking out (one green and one yellow), and in the same way the two different dipeptides are different as far as we are concerned. So if you add another amino acid, to make a tripeptide you have 20 X 20 X 20 = 8,000 combinations, and if you add a fourth amino acid to make a tetrapeptide you have 16,000 combinations.
An 'average' protein has about 250 amino acids in its chain. How many different combinations are there of 250 amino acids? Although there are billions and billions of possible combinations, actually there are less than 100,000 used in the human body according to the best estimates of the scientists.
Life on Earth doesn't use all the different possible proteins, in fact quite a lot of the proteins that we use are used by everything from bacteria up to Blue Whales (and were probably used by the dinosaurs too). But each species has some differences from the others, for example the protein that makes the muscles that flies use to fly isn't one that we make, we don't need to be able to fly.
Your genes control the order of the amino acids that go to make up your proteins. This is how mutations show themselves, suddenly a protein can have a slightly different amino acid in its chain and behave slightly or totally differently. We know that there are 20 amino acids, and if you've already read the Dynamic DNA section you know that there are four different sorts of bases that make up DNA. With this information we can work out how many DNA bases are required to code for all the amino acids. Try and work it out and then click here to read on.
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As a note for cat lovers and veterinary surgeons everywhere, cats use a 21st amino acid called taurine. They are just about the only animal that needs taurine in their diet, but if you drink any of the 'Energy Drinks' they contain taurine as well.