Lecture 2 Life Origins: Lecture Notes 2

In the 6 Kingdom view of life there are both prokaryotes (no cell nucleus) and eukaryotes (cell nucleus)
Prokaryote kingdoms: Bacteria and Archaea
Eukaryote kingdoms: Animalia, Plantae, Fungi, Protists*
* the protists will probably be eliminated from the Kingdom list soon because they have multiple points of origin

The universal tree of life (see diagram in slide 3 of Sep 14 lecture) is based on RNA sequences. 2 important observations:
- Eukarya probably descended from archaea not bacteria
- Animals, plants, and fungi represent a tiny fraction of genetic diversity of life on earth

3 Theories of the Origin of Life

1. Primordial soup hypothesis
2. Reduction in ocean vents
3. Carbon-rich meteorites (chondrites)

Miller and Urey experiment in 1953 simulated the conditions presented in the primordial soup hypothesis. They added heat and were able to form simple organic molecules. This confirms the primordial soup hypothesis; today, we still think that the primordial soup hypothesis is the most probable.

KEY CONCEPT: Crisis Management facilitates innovation in early life

The example below illustrates a cycle of crisis and innovation. Many of the advances in the origin of life have been in response to crisis.
• The earliest autotrophs likely derived their H from H2 or H2S (innovation)
• The H source became exhausted (crisis)
• So the autotrophs began to use photosynthesis and use sunlight to cleave H from H2O (innovation)
• The resulting O2 poisoned the atmophere (crisis)
• Aerobic respiration (innovation)

Other key events:

Symbiosis within a modern cell: Mitochondria (found in eukaryotic cells) have an endosymbiotic origin. Mitochondria (prokaryotes) took up residence in another cell and lived symbiotically there. Mitochondria are protected within the walls of the cell and, in turn, they release products that the host cell needs. Everyone wins.

The Cambrian explosion: after the earth melted, there was a sudden, massive radiation (explosive biological diversification) of eukaryotic phyla in oceans. Life on earth (both plant and animal) needed to make many innovations in order to move onto land. All animal phyla evolved in marine environments and most animal phyla remain in marine environments – terrestrial and freshwater animal groups are a very small subset of phyletic diversity (though a large proportion of species diversity).

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