There are an estimated 37.2 trillion cells in the human body.64 Each one of these cells performs many millions of complex reactions every second.65 In doing so the cell does not act atomistically but within complex feedback systems with other cells. Biological enzymes promote extraordinary rates of change. In the absence of catalytic enzymes, the decarboxylation of amino acids would proceed with a typical half-life of about a billion years: in the presence of enzymes these half-lives are reduced to less than a thousandth of a second.66 And a single molecule such as carbonic anhydrase – of
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