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Endosymbiotic Theory
Emily Summers…read more

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In eukaryotic cells the chloroplasts and mitochondria
have features that are similar to whole cell structures,
like they contain their own DNA that is a circle
chromosome- this is the same as prokaryotic cells-
whereas eukaryotic cells have linear DNA within a
Like prokaryotic cells they replicate through binary
fission- one cell splitting into two, whereas eukaryotes
use mitosis.
The organelles also contain ribosome's- the same size
as prokaryotes (70S)…read more

Slide 3

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Similarities Ctd
The electron transport chain of the mitochondria is found around the
plasma membrane of a mitochondrion, likewise the electron transport
chain of a chloroplast is found around the plasma membrane of a
chloroplast- so in eukaryotic cells the electron transport chain is only
present in those places, not around the membrane of the entire cell-
whereas, in prokaryotes that is the case.
Mitochondria and chloroplasts are small, around 1-10 microns, like
prokaryotes. The size of eukaryotic cells is much larger, 50-500 microns.
Eukaryotic cells, mitochondria, and chloroplasts were discovered 1.5
billion years ago, whereas prokaryotes existed long before,
Anaerobic bacteria: 3.8 Billion years ago, Photosynthetic bacteria: 3.2
Billion years ago, Aerobic bacteria:
2.5 Billion years ago…read more

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The Theory
These astonishing similarities caused Lynn
Margulis to put together a theory called, "The
Endosymbiotic theory" in the 1960's.
Endosymbiosis means that cells are not
ingested, but engulfed and have a mutually
beneficial relationship.…read more

Slide 5

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The Theory Ctd
Mitochondria adapted through the endocytosis of aerobic
Chloroplasts adapted through the endocytosis of photosynthetic
prokaryotes/ bacteria
This was very beneficial for anaerobic eukaryotes because otherwise they
could not survive in aerobic surroundings- and aerobic respiration is so
much more efficient than anaerobic respiration, giving the eukaryotes with
aerobic abilities a huge advantage over anaerobic eukaryotes.
These hybrid cells would produce offspring, and the beneficial partnership
would continue. It is thought that the two types of cells could not live
independently and then evolved together, hence why mitochondria are the
site of aerobic respiration today.…read more

Slide 6

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Serial Endosymbiosis
Most eukaryotes contain mitochondria,
although only photosynthetic eukaryotes
contain chloroplasts,
it is thought that endosymbiosis happened
twice in stages. Firstly an aerobic prokaryote
was engulfed by an anaerobic eukaryotic cell.
Then the prokaryote adapted with this
eukaryote, and evolved into a mitochondrion
Finally, a photosynthetic prokaryote engulfed
but not digested by an aerobic eukaryote (has a
mitochondrion).…read more

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