Obcells as proto-organisms: Membrane heredity, lithophosphorylation, and the origins of the genetic code, the first cells, and photosynthesis

I attempt to sketch a unified picture of the origin of living organisms in their genetic, bioenergetic, and structural aspects. Only selection at a hi gher level than for individual selfish genes could power the cooperative ma cromolecular coevolution required for evolving the genetic code. The protei n synthesis machinery is too complex to have evolved before membranes. Ther efore a symbiosis of membranes, replicators, and catalysts probably mediate d the origin of the code and the transition from a nucleic acid world of in dependent molecular replicators to a nucleic acid/protein/lipid world of re producing organisms. Membranes initially functioned as supramolecular struc tures to which different replicators attached and were selected as a higher -level reproductive unit: the proto-organism. I discuss the roles of stereo chemistry, gene divergence, codon capture, and selection in the code's orig in. I argue that proteins were primarily structural not enzymatic and that the first biological membranes consisted of amphipathic peptidyl-tRNAs and prebiotic mixed lipids. The peptidyl-tRNAs functioned as genetically-specif ied lipid analogues with hydrophobic tails (ancestral signal peptides) and hydrophilic polynucleotide heads. Protoribosomes arose from two cooperating RNAs: peptidyl transferase (large subunit) and mRNA-binder (small subunit) . Early proteins had a second key role: coupling energy flow to the phospho rylation of gene and peptide precursors, probably by lithophosphorylation b y membrane-anchored kinases scavenging geothermal polyphosphate stocks. The se key evolutionary steps probably occurred on the outer surface of an 'ins ide out-cell' or obcell, which evolved an unambiguous hydrophobic code with four prebiotic amino acids and proline, and initiation by isoleucine antic odon CAU; early proteins and nucleozymes were all membrane-attached. To imp rove replication, translation, and lithophosphorylation, hydrophilic substr ate-binding and catalytic domains were later added to signal peptides, yiel ding a ten-acid doublet code. A primitive proto-ecology of molecular scaven ging, parasitism, and predation evolved among obcells. I propose a new theo ry for the origin of the first cell: fusion of two cup-shaped obcells, or h emicells, to make a protocell with double envelope, internal genome and rib osomes, protocytosol, and periplasm. Only then did water-soluble enzymes, a mino acid biosynthesis, and intermediary metabolism evolve in a concentrate d autocatalytic internal cytosolic soup, causing 12 new amino acid assignme nts, termination, and rapid freezing of the 22-acid code. Anticodons were r ecruited sequentially: GNN, CNN, INN, and *UNN. CO2 fixation, photoreductio n, and lipid synthesis probably evolved in the protocell before photophosph orylation. Signal recognition particles, chaperones, compartmented protease s, and peptidoglycan arose prior to the last common ancestor of life, a com plex autotrophic, anaerobic green bacterium.