The 16S rRNA Tree of Life

Red = thermophiles near the root

Green = photosynthetic The 3 Domain Tree of Life was first discovered by sequencing of rRNA genes, but it was eventually accepted by biologists because it explains many other observations.

Bacteria Archaea Eukarya

Membrane-enclosed No No Yes nucleus Chromosome style Single, circular Single, circular Multiple, linear

Operons Yes Yes No

Plasmids Yes Yes Very rare

Coupled transcription- Yes Yes No translation Peptidoglycan in cell Yes No No wall Initiator tRNA Formylmethionine Methionine Methionine

DNA replication Unique Similar to Eukarya Similar to Archaea pathways RNA polymerases One One, but same kind as Three Eukarya Susceptible to Yes No No antibiotics Membrane lipids Ester-linked Ether-linked Ester-linked

Methanogens? No Yes No Further Reading

A vicious fight in 1998 between Ernst Mayr and Carl Woese on the Three Domains

Mayr: http://www.pnas.org/content/95/17/9720.full Excerpt: “Here it must be remembered that Woese was not trained as a biologist and quite naturally does not have an extensive familiarity with the principles of classification.”

Woese’s reply: http://www.pnas.org/content/95/19/11043.full Excerpt: “Finally, the disagreement between Dr. Mayr and myself is not actually about classification. It concerns the nature of Biology itself. Dr. Mayr’s biology reflects the last billion years of evolution; mine, the first three billion. His biology is centered on multicellular organisms and their evolutions; mine on the universal ancestor and its immediate descendants. His is the biology of visual experience, of direct observation. Mine cannot be directly seen or touched; it is the biology of molecules, of genes and their inferred histories. Evolution for Dr. Mayr’s is an “affair of phenotypes” (1). For me, evolution is primarily the evolutionary process, not its outcomes (20). The science of biology is very different from these two perspectives, and its future even more so.”

Also, Norm Pace’s argument to eliminate the word “prokaryote”: http://www.nature.com/nature/journal/v441/n7091/full/441289a.html

Presentation by Norm Pace about the history of Carl Woese and the Three Domains, as well as his rant about “prokaryote” being a failed concept: https://www.youtube.com/watch?v=VcfutXOBZRI