prokaryotes - Biology 5B concentrates on multicellular...

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LUCA - Last Universal Common Ancestor A recent ‘tree of life’ phylogeny: Biology 5B concentrates on multicellular eukaryotic organisms, but these are a small portion of biological diversity. Most life is unicellular , mainly prokaryotic: Three huge domains of life: Bacteria, Archaea, Eukarya LUCA - Last Universal Common Ancestor An alternate way of showing phylogenetic relationships: Eukarya Archaea Bacteria Biology 5B concentrates on multicellular eukaryotic organisms, but these are a small portion of biological diversity. Most life is unicellular , mainly prokaryotic: Three huge domains of life: Bacteria, Archaea, Eukarya Today we take a brief look at the prokaryotes : Domain Bacteria (or Eubacteria ) Domain Archaea Prokaryote phylogeny and diversity Relationships among prokaryotes were poorly understood until genetic sequencing (molecular systematics) was developed in the last few decades. Formerly thought to be a few thousand species in a single group, Monera. Now thought to comprise two separate domains, Bacteria and Archaea. These are quite different in many ways (genetics, biochemistry, etc.). Probably millions of prokaryote species, most not yet described.
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Early separation and prolonged independent evolution of Bacteria and Archaea Eukaryotes probably arose from Archaea. Prokaryote phylogeny and diversity This chart (from the text) shows a simple version of our current understanding of prokaryote phylogeny. Like all phylogenies it is a hypothesis that will likely be modified as we learn more. Differences between Prokaryotes and Eukaryotes: Prokaryotes Eukaryotes small cell size (diameter large cell size (diameter usually is 1-5 μ m) usually is 10-100 μ m) usually no membrane other numerous membranes than cell membrane, which within the cell membrane may be infolded DNA not contained in DNA in membrane-bound a discrete region nucleus small genome large genome (~100 X) few organelles (ribosome) lots of complex organelles Very ancient: 3.5+ billion years perhaps 2 billion years? Life -- especially prokaryotic life -- has a long history. First fossils of organisms date back about 3.5 billion years; the Earth itself is about 4.5 billion years old. How do we date these (and other) fossils? A century ago, we relied primarily on geological strata: older stuff in lower layers; younger stuff in upper layers. Paleontologists could put fossils into a chronological sequence , but did not have a good absolute time index. The discovery of radioactivity radioactivity provided that absolute index. Radiometric dating
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prokaryotes - Biology 5B concentrates on multicellular...

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