  Natural protein molecules are exceptional polymers. Encoded in apparently
random strings of amino-acids, these objects perform clear physical tasks that
are rare to find by simple chance. Accurate folding, specific binding, powerful
catalysis, are examples of basic chemical activities that the great majority of
polypeptides do not display, and are thought to be the outcome of the natural
history of proteins. Function, a concept genuine to Biology, is at the core of
evolution and often conflicts with the physical constraints. Locating the
frustration between discrepant goals in a recurrent system leads to fundamental
insights about the chances and necessities that shape the encoding of
biological information.
