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The Theory of Endosymbiosis

Evelyn Woodcock

Endosymbiosis is the theory that a larger host cell engulfed free-living cells and sustained a symbiotic relationship which co-evolved with the host cell into the mitochondria and chloroplasts.

The Theory

In some prokaryotic cells, the plasma membrane infolds.

-These folds are thought to have formed the endoplasmic reticulum and encased the DNA within the cell forming the nuclear envelope This would be an early prokaryote cell

Host Cell

Mitochondria

The mitochondria is thought to have originally been a proteobacterium with an oxidative metabolism which benefited the larger cell and also provided energy.

Chloroplasts

The chloroplasts are thought to have evolved from a cyanobacteria, a photosynthetic bacterium

Both of these prokaryotes would have benefited with a stable environment to thrive in within this cell

Aside from all the symbiotic relationships we see today…

Mitochondria and chloroplasts have their own membranes

and their own DNA... … and replicate through binary fission They also react to antibiotics that inhibit

protein synthesizers

What evidence?

Before biologist Lynn Margulis, organelles in cells seemed so complex, and were without explanation.

First proposed by Konstantin Mereschkowski in 1905, the theory of endosymbiosis is now widely accepted.

Mason, Kenneth A., Jonathan B. Losos, Susan R. Singer, Peter H. Raven, and George B. Johnson. "4.5, 29.1." Biology: Evolution, Diversity and Ecology: Selected Materials from Biology, 10th Edition. 10th ed. New York: McGraw-Hill, 2014. N. pag. Print.

Mikulecky, Peter, Michelle R. Gilman, and Brian Peterson. "Endosymbiotic Theory." - For Dummies. John Wiley & Sons, Inc, n.d. Web. 17 Mar. 2014. <http://www.dummies.com/how-to/content/endosymbiotic-theory.html>.

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