Topic 1 - Intro to cell biology (lec 2)

for mitochondria and chloroplast there is good

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Unformatted text preview: karyotic cells and membrane bound organelles. > For Mitochondria and Chloroplast there is good evidence as to there origins as bacteria that incorpirated into a larger prokyarote host cell. A simple prokaryote cell might have engulfed smaller aerobic prokaryote cells( Cyanobacteria). Rather than breaking down those bacteria, for some reason they didn't breakdown, but established a stable endosymbiotic relationship with the host cell. The bacteria become estabilished in the cytoplasm of the host cell. The aerobic bacteria provided the host cell energy, chemical enegry to ATP. The host cell provided the bacteria a saver, stable environment. So as a result these aerobic bacteria become stablly incorpirated into the host cell, and eventually become the organelle that we now recognize as mitochondria. It is hypothesized that a very similar event happened later on in the line that gave rise to plants and some of the protists. A second endosymbiotic happened where the cell engulfed a photosynthetic bacteria, these than gave rise to cholorplast in plants. Endosymbiont theory Mitochondria from incorporation of aerobic prokaryote Chloroplast from (later) incorporation of cyanobacterium Evidence to support this theory? See: Rumpho et al. 2011 JEB 214, 303-311 Present day examples of endosymbiosis: - symbiotic animals containing green photobionts (e.g. some sponges, Hydra, the salamander Ambystoma maculatum) - solar-powered sea slugs (kleptoplasty in Elysia chlorotica) BIO 1140 – SLIDE 19 Rumpho et al. 2008 PNAS 105, 17867-17871 Pause for reflection How does kleptoplasty in Elysia chlorotica differ from the endosymbiotic origin of chloroplasts? BIO 1140 – SLIDE 20 Can you meet these objectives? By the end of this lecture you will be able to... Answer the question: what is a cell? Describe the cell theory Describe the basic properties of cells Explain why cells are small Contrast and compare prokaryotes and eukaryotes List and briefly describe the organelles of eukaryotic cells Describe, with support, one theory on the origins of eukaryotic cells BIO 1140 – SLIDE 21 > Animals live in symbiotic relationships with plants. Some sponges that have algea stablly incorparted inside it. > Solar-powered sea slug (Elysia chlorotica), Chloroplast are incoprparted into the cells of this animal by the algea that it eats. > little tiny sea slugs are brown at first, its only after that they start feeding on algea that they become green. The green colour comes from the chloroplast. It breaks open the algea, and the cells of the intestine engulf chloroplast from the algea forming a stable symbiotic relationship. In a sea slung the intestine extends to all parts of the body, which is why the whole slug is green. (Kleptoplasty) which means stealing cholorplast. Once the slug has enough cholorplast it stops eating and it simply surives on carbohydrates that are synthesized by its cholorplast. They just use light to produce food. >Difference b/w what happens in kleptoplasty in Elysia chlorotica and in the Endosymbiotic origin of cholorplast. > In the sea slug( multicellular) chloroplast are not passed on from one generation to the next. In the endsymbiotic ( single celled) orgins of cholorplast they become stablly incorperated in the cell and passed on from one genertion to the next. > In the sea slug it is taking cholorplast that are already what we know as choloroplast. In the endosymbiotic it was photosynthetic bacterium that was engulfed and established a two way relationship with the host cell. So it turned into cholorplast over time. > The mechanism of digesten is very different. In the sea slug u are looking at a multicellular animal that has to rip up the algea to get the cholorplast cell. In the endosymbotic it was one prokaryotic cell that engulfed another....
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