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letters but in a different order, and so the words they spell out have completely different meanings. Similarly, 476,021 and 104,762 are different numbers using the same symbols laid out differently. Likewise, 001010 and 100100 have very different meanings in binary code. In exactly the same way the order of the four chemical symbols in DNA embodies the message. ‘ACGGTA’ and ‘GACAGT’ are DNA anagrams that mean completely different things to a cell, just as ‘derail’ and ‘redial’ have different meanings for us.
    So, how is the message written and how is it read? DNA is confined to the chromosomes, which never leave the cell nucleus. It is the proteins that do all the real work. They are the executives of the body. They are the enzymes which digest your food and run your metabolism; they are the hormones that coordinate what is happening in different parts of your body. They are the collagens of the skin and bone, and the haemoglobins of the blood. They are the antibodies that fight off infection. In other words, they do everything. Some are enormous molecules, some are tiny. What they all have in common is that they are made up of a string of sub-units, called amino-acids, whose precise order dictates their function. Amino-acids in one part of the string attract amino-acids from another part, and what was a nice linear string crumples up into a ball. But this is a ball with a very particular shape, that then allows the protein to do what it was made for: being a catalyst for biological reactions if it is an enzyme, making muscles if it is a muscle protein, trapping invading bacteria if it is an antibody, and so on. There are twenty amino-acids in all, some with vaguely familiar names like lysine or phenylalanine (one of the ingredients of the sweetener aspartame) and others most people haven’t come across, like cysteine or tyrosine. The order in which these amino-acids appear in the protein precisely determines its final shape and function, so all that is required to make a protein is a set of DNA instructions which define this order. Somehow the coded information contained in the DNA within the cell nucleus must be relayed to the protein production lines in another part of the cell.
    If you can spare one, pluck out a hair. The translucent blob on one end is the root or follicle. There are roughly a million cells in each hair follicle, and their only purpose in life is to make hair, which is mainly made up of the protein keratin. As you pulled the hair out, the cells were still working. Imagine yourself inside one of these cells. Each one is busy making keratin. But how do they know how to do it? The key to making any protein, including keratin, is just a matter of making sure that the amino-acids are put in the right order. What is the right order? Go and look it up in the DNA which is on the chromosomes in the cell nucleus. A hair cell, like every cell in the body, has a full set of DNA instructions, but you only want to know how to make keratin. Hair cells are not interested in how to make bone or blood, so all those sections of DNA are shut down. But the keratin instruction, the keratin gene , is open for consultation. It is simply the sequence of DNA symbols specifying the order of amino-acids in keratin.
    The DNA sequence in the keratin gene begins like this: ATGACCTCCTTC…(etc. etc.). Because we are not used to reading this code it looks like a random arrangement of the four DNA symbols. However, while it might be unintelligible to us, it is not so to the hair cell. This is a small part of the code for making keratin, and it is very simple to translate. First the cell reads the code in groups of three symbols. Thus ATGACCTCCTTC becomes ATG–ACC–TCC–TTC. Each of these groups of three symbols, called a triplet, specifies a particular amino-acid. The first triplet ATG is the code for the amino-acid methionine, ACC stands for threonine, TCC for serine, TTC for