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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
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
> 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
> 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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