lpetrich
Contributor
Among cellular organisms, the most obvious difference in cell structure is between prokaryotes (before nuclei) and eukaryotes (true nuclei), between cells without nuclei and cells with nuclei. Eukaryotic cells have a lot of structure that prokaryotic ones lack, like cell nuclei and various organelles.
Since the late 19th cy., various people have speculated that some eukaryote organelles are descendants of outside organisms that took up residence in their host cells ( Symbiogenesis), and this notion was revived in the mid-1960's by Lynn Petra Alexander Sagan Margulis (yes, she was Carl Sagan's first wife). Over the 1970's, it became well-established for two kinds of organelles, mitochondria and chloroplasts. Mitochondria turned out to be closest to alpha-proteobacteria, like root-nodule bacteria and rickettsia bacteria, and chloroplasts to cyanobacteria, formerly called blue-green algae.
The rest of the cell's origin has been a much more difficult problem.
First some background. In the 1970's, a deep split in prokaryotes was discovered, between Bacteria or Eubacteria, and Archaea or Archaebacteria. Bacteria contains most of the better-known prokaryotes, including all pathogenic ones and the ancestors of mitochondria and chloroplasts, and Archaea contains a lot of oddballs, like methanogens (they do CO2 + 4H2 -> CH4 + 2H2O), and many hydrothermal-vent organisms. Some of them are hyperthermophiles, living in very high temperatures like above the boiling point of water at sea level.
Eukaryote informational systems turned out to resemble those in Archaea and their metabolic genes those in Bacteria. Their membrane lipids contain fatty acids, like in Bacteria, instead of terpenes, like in Archaea.
But for a long time, no archaea seemed especially close to Eukarya. Did the ancestors of present-day Archaea diverge from the ancestor of the eukaryote informational system early in the history of our planet's biota?
Since the late 19th cy., various people have speculated that some eukaryote organelles are descendants of outside organisms that took up residence in their host cells ( Symbiogenesis), and this notion was revived in the mid-1960's by Lynn Petra Alexander Sagan Margulis (yes, she was Carl Sagan's first wife). Over the 1970's, it became well-established for two kinds of organelles, mitochondria and chloroplasts. Mitochondria turned out to be closest to alpha-proteobacteria, like root-nodule bacteria and rickettsia bacteria, and chloroplasts to cyanobacteria, formerly called blue-green algae.
The rest of the cell's origin has been a much more difficult problem.
First some background. In the 1970's, a deep split in prokaryotes was discovered, between Bacteria or Eubacteria, and Archaea or Archaebacteria. Bacteria contains most of the better-known prokaryotes, including all pathogenic ones and the ancestors of mitochondria and chloroplasts, and Archaea contains a lot of oddballs, like methanogens (they do CO2 + 4H2 -> CH4 + 2H2O), and many hydrothermal-vent organisms. Some of them are hyperthermophiles, living in very high temperatures like above the boiling point of water at sea level.
Eukaryote informational systems turned out to resemble those in Archaea and their metabolic genes those in Bacteria. Their membrane lipids contain fatty acids, like in Bacteria, instead of terpenes, like in Archaea.
But for a long time, no archaea seemed especially close to Eukarya. Did the ancestors of present-day Archaea diverge from the ancestor of the eukaryote informational system early in the history of our planet's biota?