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UB BIO 200 - Lecture 13

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Bio 200Lecture 13Protists- marks the arrival of eukaryotes. Eukaryotes- Chemical evidence of eukaryotes as far back as 2.7 BYA, but no true fossils untilabout a billion years later.-Originated through a evolutionary sequence that involved many steps:- Origin of a flexible cell surface- Cytoskeleton- Development a nuclear envelope that enclosed a genome that organized into chromosome- Evolution of digestive vacuoles- Engulfment of bacteria that lead to the evolution of organelles ( a theory that lead to endosymbiosis) Traits of Eukaryotes: Distinguished from prokaryotes in 3 major ways: - Multicellular, (there are single celled eukaryotes as well, but the majority are multicellular):a) Multicellular bodies allow organisms to deal with their environment in new ways because of the differentiation of cell types into organs and tissues. This allows organisms to be more flexible about the environments they encounter.- Capable of sexual reproduction:a) Sexual reproduction leads to increased genetic diversity= RECOMBINATION (promotes diversity and potentially increased the speed of adaptation).- Compartmentalized:a) Eukaryotic cells have organelles that carry out independent functions within a cell. b) These organelles were developed in a number of ways including a membrane infolding as well as engulfing other cells and hijacking their functions-The modern eukaryotic cells are kind of a cut a paste job of genes from multiple organisms and contain structures that belong to prokaryotic species.Loss of the Cell wall & Formation of Organelles:- The path toward eukaryotic cells must have begun of the loss of the rigid eukaryotic cell wall. This allowed the more fluid plasma membrane to fold into itself. It creates more surface area without increasing size. This allows larger surfaces for gas and nutrient exchange. Once the cell surface can fold in, it can also pinch off and bring items from outside the cell, into the cell= endocytosis. - Once the membrane is folded, new structures can be created. Both the nucleus and the endoplasmic reticulum are the result of membrane in-folding- The DNA of prokaryotic cells is attached to a small portion of the plasma membrane. We believe this region of attachment in-folded in a procurser to the modern eukaryote, taking the first steps towards eternal enclosure DNA in a nuclear envelope.- Once the free floating ribosomes, they attach to the infolding membranes, this is the pathway to the modern Endoplasmic ReticulumEndosymbiosis:- Means living together in close association- An ancestral eukaryotic cell, this cell engulfed aerobic energy producing bacterium. We believe it was a purple non-sulfur bacteria (Probacteria). But it did not digest it. Over time, this arrangement became permanent with the bacterium being unable to live outside the eukaryotic cell, and the eukaryotic cell being dependent on the bacterium. - Originally the bacterium probably detoxified the new the oxygen that the cyanobacteria was flooding the atmosphere with, by converting it to water. The process was coupled with ATP production and that is a process that is highly dependent on oxygen. The end result is modern Mitochondria- ATP/Energy producing powerhouse of the cell. - The same process of endosymbiosis occurred later in eukaryotic evolution with the engulfment of cyanobacteria. - The cyanobacteria then became the chloroplasts of the modern plant (photosynthesis). - Chloroplasts show an unusual form of HOMOLOGY in bacteria and in plants becauseof this endosymbiosis event.- The eukaryotic cell is a fusion of genetics for multiple species because of this extreme version of Horizontal Gene Transfer. By looking at the pattern of which organisms have mitochondria and chloroplasts, we can determine when the these endosymbiosis events happen in evolution history.Eukaryotes- Begins with ancestral protists. These organisms, they diverge in a world that was shifting’s between anaerobic and aerobic conditions, which really opened up a lot of opportunities for new organisms to evolve, such as cellular respiration- most efficient ways of producing energy.Protists: - As a group, only truly unified by all having organelles. Protists are verydiverse, far more diverse than plants, fungi and animals. - Both unicellular, multicellular, colonial, asexual, sexual protists. - Descriptive of a world in transition- The results of evolution during the rise of Eukaryotes are hugely diverse. Some authors, replace the word “protists” with “microbial eukaryotes”, really to indicate this isn’t a monophyletic group.- The genetic relationship among the protest and the most recent common ancestor of all the protists groups are also the most recent common ancestor of all eukaryotes. Eukaryotes are monophyletic, so this makes the protists paraphyletic.CddddSome protists are very closely related to fungi and animals than to other protists, and similarly with plants. This makes the protests highly paraphyletic. This eukaryotic tree shows the hypothesis for the relationships among eukaryotes:5 main groups from the tree:- The SAR, all contains protists- The Excavates, all protists- The Archaeplastida, land plants/algae - The Amoebozoans, all protists- The Opisthokonts, Fungi and animals-All of these groups are monophyletic clades.-Taxonomy doesn’t equal phylogeny! This tree highlights this. The naming of groups doesn’t follow evolutionary relationshipsTraits of Protists: - Un-unified group of organisms=Protists- Variation in protist’s traits reveal the lack of unity in this group- Locomotion: protists can move using flagella Ex:Euglena Protists can move using cilia (groups of short flagella like protrusions that wave creating water currents) Protists can move using pseudopodia (use variously shaped sticky protrusions that reach out and stick to adjacent surfaces, basically rolling the protisit across the surfaces) EX: Amoeba- Cell Surface:a) Some protists are only surrounded by plasma membrane, but many other protists have extra cellular material that is deposited on this membrane. EX: Amoeba. b) This extra cellular material shields the protists from negative aspects of environment.- Reproduction: a) Both sexual and asexual protistsa) Sexual ex: ciliatesb) Asexual ex: amoebas- Nutrition :a. Protists exhibit every type of nutritional acquisition other than chemoautrophy (only so far have been observed in prokaryotes)b. Exhibit: Photosynthesis, photoautotrophy, heterotrophy,


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UB BIO 200 - Lecture 13

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