The reaction pathways discovered by ANI-1xnr in a Miller experiment simulation for the formation of glycine from small-molecule species (for example, NH 3 , CO, H 2 O, H 2 and CH 4 ). The green arrows denote reactions previously identified by Wang et al. or Saitta and Saija. The orange arrows denote reactions that have a similar reaction in Wang et al. or Saitta and Saija. The majority of reactions have been previously reported in the literature, confirming the validity of the ANI-1xnr mechanism. Three-dimensional snapshots extracted from the MD simulation trajectory are reported in Extended Data Fig. 6 , further confirming that the reaction pathways are physically meaningful. Note that +H does not necessarily signify a free hydrogen atom, +H is short-hand for a proton donor, for example, NH 4 , NH 3 , CHO, CHNO, H 3 O or H 2 O. Likewise, -H does not necessarily signify dissociation of a hydrogen atom. -H is short-hand for a proton acceptor, for example, NH 2 , CO, CNO, H 2 O or OH. The boxes encapsulate the key intermediates, carbon dioxide (CO 2 ) and methylene (CH 2 ). The novel pathways to form these key intermediates are reported in Extended Data Fig. 7 . The depiction of bond orders and radical species is based simply on chemical intuition, since ANI-1xnr does not provide explicit bonding, orbital or electronic information (for an alternative interpretation of this mechanism involving ionic species, see Extended Data Fig. 8 ).
