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Biology 1002 Lectures 10 - 17 Outcomes

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Biology 1002B
Tom Haffie

1Lecture 10 Outcomes 1 Meaning of endosymbiosis cyanobacteria lateral gene transferEndosymbiosiso The theory that mitochondria we see in our cells today are actually from aerobic bacteriumCyanobacteriao The only group of bacteria or archaea that undergo oxygenic photosynthesis o Mitochondria came first followed by the development of the chloroplast Lateral gene transfero The transfer of genes between organisms in a manner other than traditional reproduction Ex Relocation of genes in the organelle to the nucleus 2 Origin of endomembrane system nuclear membrane ER etcEndomembrane system o Derived from the infolding of the plasma membraneNuclear membrane and the ER are derived from the infolding of the plasma membrane o Nuclear envelope is an advantagetightly control transcription and translation from the rest of the cell 3 Origin of mitochondria and chloroplastsMitochondria said to have derived from an aerobic bacterium o Ancestral bacterium was probably anaerobic so there would be an advantage to bring in the aerobic bacterium through phagocytosis to provide you with lots of ATPChloroplasts we see in modern day plants evolved from an ancestral cyanobacterium 4 Evidence supporting theory of endosymbiosisMorphologyo Mitochondria look like bacteriaFormationdivision o Mitochondria divides much like how a bacterium dividesNo gene that codes for mitochondriathe only way you get more is when they divideElectron transport chains o Happens that chloroplasts are the only organelles that have electron transport chainsGenomes o Have their own genomes o If they were once free living cells they must have their own genetic info Transcriptiontranslation machinery o Convert information and use it for synthesis of proteinsincludes ribosomes5 Factors driving development of early eukaryotic cellsOXYGENEarliest forms of life were anaerobicuses fermentation to keep glycolysis going Then you get cyanobacteria that can do oxygenic photosynthesiswhat lead to oxygen in the airThis lead to bacteria that undergo aerobic respirationthis could only develop when there was an appreciable amount of oxygen in the atmosphereo Provides much more ATP than glycolysis and fermentation6 Why eukaryotic cells can be larger and more complex than prokaryotic cells 2 Bacteria and Archaea have their centers of oxidative phosphorylation on their plasma membranes so if they try to get bigger they need more centers of oxidative phosphorylation to give them more energyProblem is that prokaryotes plasma membranes surface area increases as a function of radius SQUARED whereas the volume increases as a function of radius CUBEDVolume gets bigger much quicker than surface area of plasma membrane and so the cell tries to compensate by putting more centers of oxidative phosphorylation on the plasma membrane BUT eventually it runs out of space on the pm and that is what limits the size of prokaryotes o ie not being able to provide enough energy to support a larger cellProkaryotic cells have a HIGH plasma membrane area to volume ratio Eukaryotes can be much bigger because they have mitochondria which has many oxphos centers so you can produce more ATP and support a larger genomeEukaryotic cells have a LOW plasma membrane surface area to volume because the PM is not the site of oxidative phosphorylation 7 Evidence for lateral gene transfer from organelles to the nucleusThe gene for complex 1 in the electron transport chain is found in the nucleus instead of the mitochondria where it is expressed8 General idea about how lateral gene transfer is detected Southern blotIsolate genomic DNA run it on gel make DNA single strandedAdd a single stranded DNA probe and see if hybridization occursYou can then see what genes you have in that genomeSo you can isolate mitochondrial DNA and nuclear DNA and add the probe of Oxidase 3 mitochondrial geneIf the gene is found in mtDNA but not the nDNAlateral gene transfer has not occurredIf found in nDNA and not mtDNAlateral gene transfer has occurred If found in both LGT occurred and both genomes have a copy of the gene o You make a copy and send a copy to the nuclear genome and only after that occurs do you destroy the original copy of the gene 9 Hypotheses for why genes move to the nucleus from organelles lateral gene transferCoordinated controlput them under tighter nuclear control10 Possible reasons why certain genes have NOT moved to the nucleus from organellesNecessary gene products may not be able to be transported into the mitochondria Localizaed gene expression may have advantages over transcription in the nucleus and translation in the cytoplasm then transport into the mitochondria Some genes may be regulated within the mitochondrial environment 11 Role of cpn60 in tracing endosymbiotic and lateral gene transfer event in eukaryotesEukaryotes that dont have mitochondria like giardia and trichomonas have the gene cpn60 which is a mitochondrial protein and now found in the genome This indicates that eukaryotes without mitochondria are not evolutionary intermediates they had mitochondria and lost themIt seems the ancestor to all eukaryotes had to have mitochondria and that lateral gene transfer occurred very early on
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