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Lecture 10

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Western University
Biology 1002B
Tom Haffie

Lecture 10: Evolution of Eukaryotes All morphologically complex organisms are eukaryotic - why? Eukaryotes - Morphology, cellular structure, processes are all complex. - Bigger cells o PM (plasma membrane) is not site of ox phos. o Mitochondria is site of ox phos – generates ATP – lots of energy - can support larger genome. o Gene replication – low energy. o Protein coding/synthesis – high energy – many more proteins. Prokaryotes - Show no tendency to form organelles – no complexity. - Bacteria have stayed simple over evolution. - Why don’t they if evolution is shown to be gradual? o Cell grows bigger – need more ATP needed. o Ox phos happens on plasma membrane – as bacterium grows – need more centers of ox phos and electron transport chains on plasma membrane. Need centers for energy b.c. as V of cell increases – protein and energy demand increases. o Problem: as cell gets bigger - V increases much faster than SA. Can’t fill plasma membrane with enough ox phos centers to fulfill ever-increasing V. Therefore, bacteria size stays small. - Bacteria: High PM SA/V – constrains size. - Euk: Low PM SA/V - Energy constrains complexity – need energy to synthesize proteins for complex functioning. - Genome size is low energy so simple organisms can have very large genomes however it takes energy to maintain genome size so proks keep genome size small. The Paradox - All morphological complex life is eukaryotic. - All eukaryotes share common complex traits. o Nucleus, trafficking, cytoskeleton, sex, phagocytosis, organelles, etc.  meaning of endosymbiosis, cyanobacteria, lateral gene transfer Endosymbiosis - Mitochondrion and chloroplasts are derived from free-living prok cells (aerobic bacterium). - Not derived from same place nuclear envelope is derived. Cyanobacterium - Chloroplasts with which plants make food for themselves is actually a cyano living within the plant’s cells. - Endosymbiosis: cyano began to live in euk cells, making food for euk host in return for a home – origin of euk mitochondria. - Descendent for chloroplasts - identical photosynthetic structure to chloroplasts. - Small, unicellular, oldest known fossil, oxygen atmosphere generated by numerous cyanobaterium in archaean era.  origin of endomembrane system, nuclear membrane, ER etc. Endomembrane System - Includes nuclear envelope and ER - Derived from infolding of plasma membrane - Nucleus separates genomic info. o Nuclear envelope – regulates transcription and replication of DNA. Eg. Transcription factors. - Nuclear envelope and ER are distinct from Endosymbiosis  origin of mitochondria and chloroplasts  evidence supporting theory of endosymbiosis - 1. Morphology – looked the same - mitochondria and ch
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