How Science Works: Evolution by John Ellis

Author:John Ellis
Language: eng
Format: epub
Publisher: Springer Netherlands, Dordrecht

Proteins are linear polymers of twenty different kinds of amino acid, strung together like beads on a chain. Each chain is called a polypeptide and has a unique sequence of amino acids. Because there are twenty different kinds of amino acid found in proteins, and the length of chains can be anywhere between about 50 and 500 amino acids long, the total possible number of unique chains is very large. If we take the average length of a polypeptide chain as 300 amino acids, there are 20300 possible sequences. This number is much larger than the estimated total number of fundamental particles in the entire observable universe (~1080). So many more different kinds of protein are possible in principle than have actually appeared in evolution. We now have the genetic engineering technology to make any of these novel proteins, and some of them may well turn out to be useful.

How does the unique sequence of amino acids in the chains of a given protein determine the specific properties of that protein? The answer is that this sequence determines how each chain folds into a specific three-dimensional shape, called its conformation. Figure 5.1 shows a model of the specific conformation of one molecule of the enzyme hexokinase.

Fig. 5.1Conformation of the enzyme hexokinase before and after binding glucose

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