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Transcript
The Dawning of Eukaryotes How Our Cells Came to Be What is a Eukaryote? Organism with membranebound organelles – most notably a nucleus Where did the Nucleus come from? We’re really not sure. A couple of main theories 1. An Archaean invading a Bacterium Archaeans share many genetic features with eukaryotes Bacteria show some structural similarities to eukaryotes 2. A bacterium evolved A species of bacterium (planctomycetes) have primitive internal organelles Maybe a relative of this species evolved more complex internal membranes? 3. A virus invaded a primitive cell Explains linear chromosomes Some algae can infect hosts with a copy of their nucleus Could explain all life forms, eukaryotes just had a more complex cell that was invaded 4. A simple cell evolved an extra outside membrane The original cell became the nucleus Nuclear pores evolved that let ribosomes out of the nucleus and into the cell (ribosomes are made in the nucleus) Mitochondria and Chloroplasts We have a better idea of how they came to be by endosymbiosis This could have happened before or after the formation of the nucleus Endosymbiosis Mitochondria and chloroplasts were free living bacteria There are bacteria capable photosynthesis/aerobic respiration Somehow a cell took in the bacteria They lived symbiotically together Over time the cell came to control the mitochondria/chloroplast Evidence for Endosymbiosis Mitochondria/chloroplasts: contain their own circular DNA contain their own ribosomes (similar to bacterial ribosomes) reproduce independently similar to binary fission Many other metabolic and structural similarities Some algae contain a chloroplast with a peptidoglycan containing cell wall The Rest of the Organelles? Probably evolved from pockets forming from the nuclear membrane ER, Golgi, Lysosomes, Peroxisomes, Vacuoles etc. all can share and combine membrane Advantage of Internal Organelles Efficiency! The cell is compartmentalized so each space has what it needs I.e. the enzymes for aerobic respiration are concentrated in the mitochondria Allows our cells to grow bigger, do more things and build more complex structures Organelles Analogy Poster – Due Wednesday As a group, think of an analogy for the cell. i.e. a city Think of what in your analogy has an analogous function to each organelle (i.e. the mayor’s office is the nucleus, the power generators are the mitochondria, the solar panels are the chloroplast etc.) Make a simple poster representing your analogy. Focus on FUNCTION – not on appearance Minimum Organelles Plant Animal Nucleus Nucleus Plasma membrane Plasma membrane Cell Wall Ribosomes Ribosomes Mitochondria Chloroplast Smooth ER Mitochondria Rough ER ER Golgi Golgi Lysosome Vacuole Peroxisome Nucleolus Cytoskeleton Cytoskeleton Nucleolus