Dr. Hyman Hartman of MIT will be presenting a seminar entitled The Origin and Evolution of Photosynthesis.

Abstract:

The origin and evolution of photosynthesis is considered to be the key to the origin of life. This eliminates the need for a soup as the synthesis of the bioorganics are to come from the fixation of carbon dioxide and nitrogen. No soup then no RNA world or Protein world.  Cyanobacteria have been formed by the horizontal transfer of green sulfur bacterial photoreaction center genes by means of a plasmid into a purple photosynthetic bacterium.

The fixation of carbon dioxide is considered to have evolved from a reductive dicarboxylic acid cycle  (Chloroflexus) which was then followed by a reductive tricarboxylic acid cycle (Chlorobium) and  finally by the reductive pentose phosphate cycle (Calvin cycle).

The origin of life is considered to have occurred in a hot spring on the outgassing early earth. The first organisms were self-replicating iron-rich clays which fixed carbon  dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving systemwhich allowed the synthesis of nucleotides and phospholipids.

If biosynthesis recapitulates biopoesis, then the synthesis of amino acids preceded  the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides. Thus the origin and evolution of the genetic code is a late development and records the takeover of the clay by RNA.

Faculty Host: Dr. Marcelo Guzman