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Origin of Eukarya and Protists Notes

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University of Alberta
Biology (Biological Sciences)

January 28, 2013 - Lecture #8: Origin of Eukarya/Protists  Mutualism ( ++) o both species benefits  Competition (--) o Both species suffer form each other’s presence  Predation (-+) o One species eats another o Does kill the food item  Parasitism (-+) o One species steals nutrition from another o Doesn’t necessarily kill the food source  Commensalism (0+) o One species is not affected by the other, whereas the other speciies benefits  Amensalism (0-) o Species A harms B, but species B does nothing for A  Ex: a cow crossing a stream steps on a snail Ecological relationships  Symbiotic relationships o Occur when members of two species live in close (and often obligatory) contact with each other  Syn = together  If one species is larger than the other, it is called the host  Many proks are symbiotic o If it is inside the host organisms it is endosymbiotic  Endo = within Origin of Eukarya  First euk arose billions of years after proks first appeared  Euks differ from proks in several ways: o Have DNA in linear chromosomes in membrane bound nucleus o They have membrane-bound organelles  For example: mitochondria and plastids o They are larger than proks  Original hypothesis: euk cells arose from prok. Ancestors  However, there is now evidence indicating endosymbiosis played a role  the ancestral host cell developed some structures gradually, by infoldings of cell membranes o Such as ER, nuclear envelope  (?) Then, the ancestral host cell took on an endosymbiotic aerobic heterotrphic prokaryote o (probably a proteobacteria that uses oxygen and organic matter to make energy  probably became mitochondria) Origin…  ancestors of animals, fungi and numerous protists stopped a this point riginally hypothesized that  other lineages, engulfed photosynthetic proks eukaryotic cells arose o most likely cyanobacteria o use light and CO2 to make gradually from a prokaryotic organic compounds ancestor  these went on to become photosynthetic protists and plants • ut now evidence that serial endosymbiosis played a role • ncestral host cell developed (?) Evidence for endosymbiosis some structures gradually by 1. mitochondria and chloroplasts have their own DNA which they replicateoldings of cell membrane independently of nuclear DNAig. 25.9 in part 2. the DNA is circular (inside mitochondria and chloroplast) as is prokaryoticasmic reticulum DNA 3. Plastids (ex. Chloroplasts) have 2 or more cell membrane layers – nuclear envelope a. 2 if engulfed as ‘free’ cyanobacterium – plants and some protists b. greater than 2 if euk. engulfed other euk – some protists c. so plastids have several independent origins Summary of origin of domains Summary of Origin of Domains • lhough only three chloroplastic  although only three instances of horizinstances of horizontal fuses with through endosymbiosis shown in simplified figure… ancestor of  … the true tree would look much more tangled if the through green plants endosymbiosis shown in various plastid-bearing single-celled organisms were included simplified figure... • ..t.he true tree would look 3. origin of 2. possible much more tangled if the mitochondria archaeanf Waves of Diversification various plastid-bearing and 1. last common ancestor bacterial single-celled organisms to all living things cells to yield  metabolic diversification of the prokswere includedfor ancestor of second wave of diversification eukaryotes  second wave catalyzed by greater structural diversity of Fig. 25.18 from 7 Edition of Campbell & Reece euk. cell  third wave of diversification followed origin of multicellular bodies in several euk. lineages  another important change is that euk. cells developed new ways of reproduction o via. Mitosis, meiosis and syngamy o Mitosis vs. Meiosis Mitosis vs Meiosis chromosomes original cell: 2n = 4 chromosomes diploid duplicate duplicate diploid one diploid one diploid cell divides cell divides twice to form once to form four haploid two diploid (1n) cells (2n) cells (reduction (Maintenance division) division) (diploid) 2 diploids 4 haploids 2 x (2n = 4) gametes (e.g. eggs, sperm) Fig. 13.9 4 x (1n = 2) (haploid) Syngamy  occurs when two 1n gametes fuse together o syn = together, gam= gamete  forms 2n zygote (fertilized egg) diploid o zygo = twinned  zygote grows by mitotic cell division to form multicellular embryo  further growth may lea
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