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protists - Origin of eukaryotes Origin of eukaryotes First...

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First question: what was the origin of eukaryotes? presumably from a prokaryote ancestor, probably an Archaean: LUCA -Last Universal Common Ancestor Origin of eukaryotes First question: what was the origin of eukaryotes? presumably from a prokaryote ancestor, probably an Archaean. Some recent research suggests eukaryotes came from a ‘merging’ or ‘sharing’ of genomes from both bacterial and archaean ancestors: “Ring of life” concept: Origin of eukaryotes Second question: How did the internal structure of eukaryotes -- lots of complex organelles and nucleus -- arise? formation of endomembranes (membranes inside the cell membrane, especially around the DNA): DNA Cell membrane infolds…. and internalizes Ancestral prokaryote Origin of eukaryotes This can be seen in many living prokaryotes Second question: How did the internal structure of eukaryotes -- lots of complex organelles and nucleus -- arise? Origin of eukaryotes Internalized membranes (especially around DNA = nucleus ) Engulfing (phagocytosis) evolution of of heterotrophic aerobic mitochondrion prokaryote Endosymbiosis: other organelles (e.g., chloroplasts ) evolved similarly
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Evidence for the endosymbiont concept of the origin of eukaryotes. many organelles (chloroplast, mitochondrion) still contain some DNA, retained from independent ancestors. symbioses (mutually beneficial cooperations between species) are very common; we will see many examples in both plants and animals. Origin of eukaryotes Protists are a very diverse group of unicellular eukaryotes ‘Plant-like’ protists: photosynthetic autotrophic nutrition (carbon fixation from solar energy) Protozoa’: ingestive, heterotrophic nutrition (as opposed to photosynthetic autotrophs) Unicellular (but sometimes colonial), often with complex and unique organelles. Many modes of locomotion: pseudopodal, flagellar, cilia; organisms may be sessile, crawling, or swimming Very ancient (originated possibly > 2 billion years ago); almost certainly ancestral to metazoan animals and plants. The Protists: independent life as a single cell The Protists: independent life as a single cell Protistan phylogeny is complex and constantly revised with new data. They originated ‘deep’ in the “tree of life”. Amoebozoans ( amebae ) Gymnamoebas, etc. free-living in many habitats. Entamoebas are parasites (i.e., amoebic dysentary). No shell, cillia, or flagella; instead has Pseudopodia , extensions of cytoplasm shaped by microtubules and microfilaments . Grows by cytoplasmic streaming; cytoplasm undergoes reversible phase changes from solution to gel. Used for locomotion, and to trap food particles which are then internalized by infoldings of the cell membrane ( phagocytosis ).
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Amoebozoans ( amebae ) Other features: Food vacuoles (digestion of phagocytosed food) Contractile vacuole (removes excess water and wastes -- excretory organ ). Dumps a
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