Lecture 32 Biologists study protists 11 19 2012 To understand how eukaryotes multicellularity and sexual reproduction evolved Because protists have key roles in marine ecosystems Because some protists cause diseases in plants humans and other organisms Protists are extraordinarily abundant in aquatic food chains important producers and 1st degree consumers Eukaryotic cells represent a big change in size and complexity Shared derived traits Nucleus Mitochondria Cytoskeleton Endosymbiosis Theory Hypothesis for how mitochondria evolved by Lynn Margulis o These organelles were once free living bacteria that had entered into a symbiosis with an ancestral eukaryotic cell 2 Gya ATP cells 1 Eukaryotic cell surrounds and engulfs bacterium 2 Bacterium lives within eukaryotic cell 3 Eukaryote supplies bacterium with protection and carbon compounds Bacterium supplies eukaryote with Does the evidence support the Endosymbiotic theory o Mitochondria and chloroplasts are about the size of bacterial o Both organelles divide by binary fission o Both organelles have their own ribosomes and these are similar in structure to bacterial ribosomes o Both organelles have their own genome a circular chromosome like bacteria do o Both organelles have double membranes consistent with the engulfing mechanism Margulis also predicted that Mitochondrial gene sequences would be much more closely related to the DNA sequences from bacteria than to sequences from the nuclear DNA of eukaryotes indicating that the mitochondrial genome came from a bacterium rather than a eukaryote Similarly chloroplast genes should resemble cyanobacterial genes more closely than they resemble plant genes The Eukaryotes The eukaryotes include the protists land plants fungi and animals Protist is no longer considered a valid taxonomic group the word simply means all the eukaryotes that aren t fungi green plants or animals Protists are NOT a monophyletic group Protists can be unicellular or multicellular with or without cell walls free living or parasitic autotrophic or heterotrophic They are diverse in morphology and ecology Eukaryotes ARE a monophyletic group Protist a diverse group of organisms that are ubiquitous in moist habitats Diverse morphologically Vary in types of organelles they contain o May be unicellular or multicellular and the may have a cell wall or other external covering or no such covering Vary widely in terms of how they reproduce and how they find food Many can reproduce both sexually and asexually Many are photosynthetic with others contain carbon compounds by ingesting food or parasitizing other organisms Secondary Endosymbiosis When a predatory protist obtained a chloroplast by engulfing a photosynthetic protist but not digesting it The chloroplasts in these protists are surrounded by FOUR membranes instead of two This has happened several times during the evolution of photosynthetic eukaryotic lineages MALARIA The worlds most chronic public health problem is caused by parasites in the genus Plasmodium Parasite with complex life cycle 4 species infect humans Hosts mosquitos and humans Symptoms fever chills nausea anemia coma and death 800 000 children 5 years old die annually from malaria 1M total deaths a year 300 M new human infections year evolution of resistance by parasite to antimalarial drugs no vaccine yet parasite has high mutation rates Possible solutions o Mosquito repellant nets o Insecticides to control mosquitos o More effective drugs to combat evolution of resistance by plasmodium o Vaccines not yet for malaria How does the knowledge of phylogenies help us devise novel treatments Most dinoflagellates are unicellular About half the dinoflagellate species are photosynthetic Apicomplexa are parasitic In some species the former chloroplast apicoplast has evolved a new function Targeting the parasite s residual chloroplast apicoplast proteins with new drugs 11 19 2012 11 19 2012