Life on earth uses perhaps 5m different proteins. It is by no means clear what each of them does. In even the simplest bacterium there are proteins with jobs that scientists cannot identify-but which the bacterium clearly considers vital, since without the genes for those proteins it dies. But if many specifics are still hazy, the cumulative capability of all the things that natural proteins can do is well known: it is the living world. All the chemical and physical cleverness that life is capable of, from dandelion seeds to coral reefs, jellyfish to brains, is there because proteins did stuff.
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