Biology lecture 2/18/15 and 2/20/15Intro to Eukaryotes1. Eukaryote origins- 1° and 2° Endosymbioses- Eukaryote super2. Supergroup ExcavataDomain Eukarya (Eukaryotes): protest, fungi, animal, plantsThe eukaryotes exhibit (among many other traits) an array of intracellular membrane-bound organellesThe eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by theribosomesThe endomembrane system regulates protein traffic and performs metabolic functions in the cellMitochondria and chloroplasts change from one form to anotherOrigins of Eukaryotes- Oldest confirmed fossils: 2.1 billion years of ageEndosymbiotic hypothesis: a well-supported explanation for the origin of eukaryotic cell complexityPrimary endosymbiotic event: Origins of mitochondria and chloroplastsOnce free-living, prokaryotes reside inside other prokaryotesThey evolved to become mitochondria/chloroplasts proposed events comprising primary endosymbiotic events: origins of nuclei, mitochondria, chloroplasts1. Heterotrophic anaerobic prokaryote: new formation of the nuclear membrane2. Anaerobic “prokaryote” ingests aerobic prokaryote: mutualistic symbiosis → → obligate endosymbiont → → mitochondria3. Aerobic eukaryotic heterotroph forms symbiosis with photosynthetic cyanophyte → → chloroplastsEvidence supporting endosymbiotic origin of chloroplasts and mitochondria1. Membranes contain proteins homologeous with prokaryotes2. Divide via binary fission3. Possess single, circular DNA molecules 4. Sensitive to certain classes of antibioticsSecondary endosymbiotic eventsSome photosynthetic eukaryotes appear to have evolved recently via eukaryote – eukaryote endosymbiosis5 current “supergroups” of eukaryotes: Excavata, Chromalveolata, Rhizaria, Archaeplastida, Urikonta, NOTE: the majority of organisms in these 5 supergroups were formally grouped together in the kingdom ProtistaFormer “protists” are listed as members of eukaryote supergroups best interpreted as “phyla”Eukaryotes: former protists1. Supergroup Excavata- Diplomonads, parabasalids, englenozoans,Eukaryote supergroups: 2°endosymbioses: Euglenozoans (Excavata), Dinoflageliates, Apicomplexans, ciliates, Diatoms, Golden algae, Brown algaeSupergroup Excavata- Exhibit concave region on one side of the cell- All are unicellular- Some distinguished by reduced mitochondria- Sometimes viewed as most archaic of eukaryotes- Phylogenetic status: uncertain3 groups (phyla): Diplomonads, parabasalids, euglenozoansPhylum diplomonadida: Primarily parasitic, 2 nuclei, reduced mitochondria: mitosomes, anaerobicExample: Giardia intestinalisPhylum parabasalia: Parasitic or mutualistic symbionts, also reduced mitochondria: hydrogenosomes, flagellate and with “undulate membranes”Examples: Trichomonas, TrichonymphyPhylum Euglenozoa: Metabilically diverse (hetero/autotrophic; parasitic/free-living), distinguished by crystalline rod in flagella2 groups of subphyla in phylum Euglenozoa: Kinetoplastids and EuglenidsKinetoplastids: heterotrophic: free living, distinguished, by mitochondrial DNA: Kinetoplast (kDNA)Euglenids: autotrophic or mixotrophic: facultaively photosynthetic or heterotrophic, derived via 2° endosymbiosis: green algae + heterotrophDistinctive cellular/biochemical features of Eugenids: 2 unequal flagella, pellicle, phototacticPellicle: protein-based structure beneath plasma membraneSupergroup chormalveolata: 2 distinct clades: alveolata-stramenopila, derived voa 2° endosymbiosis: red algae + hetertrophic eukaryote, most are photosyntheticClade alveolata: autotrophic, mixotrophic, heterotrophic, distinguished by membrane-bound: aveoli at cell apex, 3 phylaDinoflagellates: freshwater/marine “algae”; autotrophic or heterotrophic, important components of the plankton community“Dinophyte” distinguishing features: chromosomes condensed throughout cell cycle, cellulose plates (theca) interior to plasma membrane, flagella (2) insertion is lateral furrowDinophyte ecological significance: primary production (oxygenic Ps) red tide/paralytic fish poisoning, Pfiesteria: a predatory protestRed tide: result of dinohpyte population explosion, cells possess high levels of carotenoidsFormulation of Red Tide: dinophytes secrete neurotoxin: saxitoxin → invertebrates accumulatehigh saxitoxin levels (unaffected) → invertebrate predators (vertebrates) develop poison symptoms → paralytic shellfish poisoning (PSP)Dinophyte ecological significance- Primary production (oxygenic Ps)- Red tide/paralytic fish poisoning- Pfiesteria: a predatory protestQuizlet link: