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Human Body

10 And dnA cooking up shapes in the protein kitchen Down in molecule sea, DNA functions as a cookbook. Written in a fourbase alphabet, a c g t, our six billion base genome is 97 rhythmic, mainly long tatarich passages. Amidst this babble the odd coherent recipe for a shape pops up, as a readable string of three letter codons, like tacgtcgagcctcacgttcatctctaattgcccatc. The recipes are for chains of aminoacids, which form proteins, the next level of molecular shape and function. DNA also holds recipes for RNA, her busy singlestranded, singleuse sister, who runs the kitchen and makes all the utensils. She copies recipes, chops and peels, and builds multiprotein dishes, while dreamy DNA just lets herself be read, replicated, and rarely modified. DNAs two helixes are mirror images, because the bases pair off, at and cg, linked by hydrogen bonds across the spiral innerspace. RNA reads one thread, the backup side coding for any necessary repairs, and enabling the twin zipper to supercoil into a superhelix. A gene is a set of recipes coding for a finished protein or RNA, and switches on when all segments uncoil, unzip, and are read. Most of the time DNA lies partially coiled inside the nucleus, only assuming the familiar X shape during cell division, when two copies of a replicated chromosome are still joined at the hip. Knowing how short one life is, DNA hops across chromosomes, species, and generations. Viruses hijack your kitchen, while bacteria pass on their crazy new recipes, helping evolution along. Many of our recipe ideas derive from evolutionary pioneers like seasquirts, lungfish and millipedes, to whom we owe much of our structure. 11
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