AP Bio Endosymbiosis

Origins of compartmentalization…

• membrane bound organelles evolved from previously free living prokaryotic cells via endosymbiosis.

• prokaryotes have internal regions with specialized structures and functions.

• eukaryotes maintain internal membranes that partition cell into specialized regions.

Eukaryotic cells- genetic chimeras…

• mitochondria and chloroplast were originally independent prokaryotic cells.

• were engulfed by larger heterotrophic cell by endocytosis

• instead of being digested, they are kept alive and continue to carry out aerobic respiration and photosyntehsis.

• overtime, some genes from mitochondria and plastids transferred to nucleus maybe through transposable elements.

Support for endosymbiont theory…

• both mitochondria and chloroplast:

  • grow and divide independent of the cell through a process similar to binary fission. 

  • have own naked loop of DNA, like prokaryotes.

  • synthesize some of their own proteins, enzymes using 70s ribosomes.

  • metabolism and DNA sequence resemble some eubacteria.

How does the endosymbiotic theory account for the origins of the following eukaryotic organelles?

• doube membranes with inner membrane similar to bacterial plasma membranes:

• mitochondria:

  • the inner membrane is folded into cristae similar to mesomes of prokaryotes.

• chloroplasts:

  • they have membranes folded into stacks of thylakoids similar to structures containing chlorophyll in prokaryote.