"The genetic code" (The Charles West Lecture)

Date:
1964
Reference:
PP/CRI/H/3/14
Catalogue details

Licence: In copyright

Credit: "The genetic code" (The Charles West Lecture). Source: Wellcome Collection.

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    let us consider briefly the elementary chemistry of pro teins. Proteins are an enormous family of molecules, but they are all built on the same general plan. Each one consists of a polypeptide chain, having a regular repeating sequence of atoms, with side chains attached at regular intervals. You could hardly have a simpler basic structure. However these side chains are not all the same. Each protein has a charac teristic length of chain, usually several hundred residues long, but there are only twenty different kinds of side chains common ly found in proteins. A protein is in fact made by joining together amino-acids with the elimination of water. The twenty kinds of amino-acid are joined together - head to tail - to give long polypeptide chains. Each particular protein - your own haemoglobin, for example - has a particular sequence of these amino-acid residues along its backbone. Proteins, therefore, from this point of view are remarkably simple. How does it come about then that they are so impor tant? They are important because, as I have said, they act as highly specific catalysts and they do this because they can form intricate and subtle three-dimensional structures. I have spoken as if the chain was fully extended, but this is not so. In general, the chain folds up into helices which then fold on themselves to make cavities lined with active chemi- dkv ÌÌMjùpLUa-, dur , cal groups. 2^ has a complicated three-dimensional structure which holds the haem group, whose function is to carry the oxygen molecule. It is an interesting fact that this enormous structure is needed just to hold a small molecule of oxygen. The reason for this is quite simple - proteins are the main things the cell knows how to make. Everything else has to be made by proteins. It is much more difficult to synthesize the relatively small haem (because it requires several enzymatic
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