  Organic molecules are widely present in the dense interstellar medium, and
many have been synthesized in the laboratory on Earth under the conditions
typical for an interstellar environment. Until now, however, only relatively
small molecules of biological interest have been demonstrated to form
experimentally under typical space conditions. Here we prove experimentally
that the condensation of carbon atoms on the surface of cold solid particles
(cosmic dust) leads to the formation of isomeric polyglycine monomers
(aminoketene molecules). Following encounters between aminoketene molecules,
they polymerize to produce peptides of different lengths. The chemistry
involves three of the most abundant species (CO, C and NH$_3$) present in
star-forming molecular clouds, and proceeds via a novel pathway that skips the
stage of amino acid formation in protein synthesis. The process is efficient,
even at low temperatures, without irradiation or the presence of water. The
delivery of biopolymers formed by this chemistry to rocky planets in the
habitable zone might be an important element in the origins of life.
