Touching Lives - March 2006
Proteins — essential to the human body
We all know that proteins have to be part of our diet; that both plants and animal foods contain protein, and that we, being animals, are partly made from protein. But what is a protein?
They are big molecules containing many thousands of individual atoms, mainly carbon, hydrogen, oxygen and nitrogen, some sulphur and phosphorous, and sometimes a metal. In comparison, sugar (sucrose) contains only 45 atoms. Each of these giant molecules is made up of long chains of amino acids. You can think of the protein molecule like a very long Meccano model, constructed from a large number of quite small parts. We need about 20 different amino acids, some of which our body can make, to construct the 100,000 or so different proteins in our bodies.
The analogy to the model is even closer — had you bolted all the components together into an inconveniently long strip, you might want to fold it up into a shape, which is now 3D and could contain features like spirals, which might be caused by the way the individual components (amino acids) had been arranged in the chain. ^It is both the composition and the shape of a protein molecule, which determines its function.^
We have to make the proteins we need from the amino acids in our food, most of which come from protein we have digested, but our bodies cannot take on pre-constructed proteins. They have to be broken up into their individual amino acids. Some of this work is done by proteases, themselves proteins, but, continuing the Meccano analogy, fitted with little spanners and screwdrivers which can undo the joints between pairs of components, and produce a heap of individual amino acids, ready for reassembly, or “burning” to provide us with energy.
The ending ‘ase’ (like in protease) applies to special substances in the body which can break up big molecules into smaller manageable bits. For instance amylase breaks up starch, and lipase breaks up fats. There is not enough room to list all the things proteins do.They are part of our structure and there is no function of a living organism which does not involve a protein.