Tree of Life: Prokaryotes and EukaryotesTree of Life: The Big PictureTree of Life: The Big PictureSlide 4ProkaryotesEukaryotesTree of Life: MicroorganismsTOL: VirusesSlide 9TOL: VirusesTOL: ProkaryotesTOL: ProkaryotesSlide 13TOL: Prokaryotes (examples)TOL: BacteriaTOL: ArcheansTOL: EukaryotesSlide 18Slide 19TOL: EndosymbiosisSlide 21Slide 22Slide 23Slide 24Tree of Life:Prokaryotes and EukaryotesBiology/Env S 204Spring 2009Tree of Life: The Big Picture•The deepest divisions of life are very old•The ancestors of all current diversity were single-celled and prokaryotic•Prokaryotes had evolved by 3.5 billion years ago and ruled the planet for about 2 billion years•Eukaryotes appeared about 1.25 billion years agoTree of Life: The Big PictureEukaryotesArcheansBacteriaca. 4 byanowViruses?Tree of Life: The Big PictureProkaryotes vs. EukaryotesBacteriaArcheans(Archaea,Archaebacteria)Protists(Protoctists)FungiAnimalsPlantsViruses?Prokaryotes•One-celled, no compartments within the cell (no nucleus)•Genetic material in a single, circular chromosome•Therefore only 1 copy of each gene per bacterium•A typical bacterium has 1,000-2,000 genesEukaryotes•One-celled or many-celled, with compartments (e.g., a nucleus is present)•Genetic material in two to many linear, separate chromosomes in the nucleus•Normally two copies of each gene present in an individual in part of the life cycle•A eukaryote has about 50,000 genes on average•Much less metabolic diversityTree of Life: Microorganisms Microorganisms are microscopic in size; include all prokaryotes (bacteria, archeans) and the single-celled eukaryotes (most protistans, some fungi, and some plants) as well as viruses.TOL: Viruses•Debate over whether viruses are living organisms or not•Some argue that they are pieces of genomes and therefore non-living biological entities•Others argue that viruses are degenerate lineages of bacteria living as obligate parasitesTOL: Viruses•But viruses are functional biological units (protein coat + genetic material)•They:–Have genetic material–Replicate (but not independently)–Evolve–Occupy specific ecological niches–Exhibit variabilityCa. 5,500 species formally recognizedEst. 500,000 species existSo only 1% are knownTOL: VirusesTOL: Prokaryotes•Two lineages: Bacteria and Archaea•Both are ancient•Most primitive members of each group are thermophiles (heat-lovers) suggesting that the common ancestor was also thermophilic•Differ mainly in membrane and cell wall structure, genes controlling protein manufactureTOL: Prokaryotes•Great metabolic diversity•Extremely important ecologically then and now•Responsible for the formation of the early atmosphere on Earth•Now control many key steps in nutrient cycles (e.g., nitrogen cycle)TOL: Prokaryotes•About 10,000 “species” recognized and named•Estimated to be anywhere from 400,000 to 3,000,000 species•Still no widely accepted species concept•“It’s a prokaryote world.” (Stephen J. Gould)TOL: Prokaryotes (examples)BacteriaCyanobacteria (blue-green algae)Purple BacteriaNitrogen-fixing bacteriaActinomycetesvarious groups of disease- causing bacteriaArcheans (Archaea)Thermophiles (heat-lovers)Halophiles (salt-lovers)TOL: Bacteria•Widespread•Exhibit a wide variety of metabolisms•Important as producers, decomposers, disease-causing organisms and in nutrient cycling (e.g., nitrogen fixation)•May form symbiotic relationships (e.g., E. coli; lichens)TOL: Archeans•Typically found in many extreme environments•More widespread than previously thought•Includes extreme thermophiles (hot springs), methanogens (anaerobes), and halophiles (very salty habitats)•Thermus aquaticus is the source of Taq polymerase used in PCRTOL: Eukaryotes•First appeared about 1.25 billion years ago•Probably arose several times through independent endosymbiotic events•Earliest lineages are all microbial•Almost all exhibit sexual reproduction•Vast majority of known biodiversity is eukaryotic but we know some groups a lot better than othersTOL: Eukaryotes Two main hypotheses explain the evolution of the nucleus:–Infolding of cell membrane in a prokaryote to enclose the genetic material–Capture of another prokaryote (endosymbiosis)TOL: Eukaryotescircular chromosomeprokaryotic cellproto-eukaryotic cellnucleuslinearchromosomesTOL: Endosymbiosis•Endosymbiosis = capture or lasting association of a prokaryote within a cell•Capture of a prokaryote able to do aerobic respiration mitochondria•Capture of a prokaryote able to do photosynthesis chloroplastsTOL: Endosymbiosisnucleus+aerobically respiringbacteriumcircularchromosome(not to scale)eukaryotic cellable to doaerobic respiration(a consumer)cell with anucleusTOL: Endosymbiosis+photosyntheticbacteriumcircularchromosomeeukaryotic cell(a consumer)eukaryotic cellable to do photosynthesisand aerobicrespiration(a producer)(not to scale)TOL: Endosymbiosis•Mitochondria and chloroplasts have their own genetic material (just like their bacterial ancestors) and they can replicate (eukaryote cells normally have multiple mitochondria and chloroplasts)•Endosymbiosis leading to mitochondria may have happened only once, but it happened a number of times leading to chloroplasts•Lineages have also lost their chloroplastsTOL: Eukaryotes1) Protists (protoctists)2) Plants3) Fungi4)