AP Bio Chapter 2.11: Origins of Cell Compartmentalization

Comparison of Compartmentalization in Prokaryotic and Eukaryotic Cells 

• Both cell types have a plasma membrane that separate their internal environment from their surrounding environment

• Prokaryotic cells have an internal region, nucleoid region, that contains its genetic material 

• Eukaryotic cells have additional internal membranes and membrane-bound organelles that compartmentalize the cell 

  • Genetic material is contained within a membrane-bound nucleus 

The evolution of membrane-bound organelles 

• The nucleus and other internal membranes (ex ER) are theorized to have formed from the infoldings of the plasma membrane 

• Mitochondria evolved from previously free-living cells via endosymbiosis 

  • A free-living aerobic prokaryote was engulfed by an anaerobic cell through endocytosis 

  • The engulfed prokaryotic cell did not get digested by the engulfing cell; this arrangement became mutually beneficial 

• Chloroplast evolved from previously free-living prokaryotic cells via endosymbiosis 

  • A free living photosynthetic prokaryote was engulfed by another cell through endocytosis 

  • The engulfed prokaryotic cell did not get digested by the engulfing cell; but rather each benefited from the arrangement 

  • Over time, the engulfed cell lost some of its independent functionality and became the chloroplast of the eukaryotic cell 

The relationship between the function of endosymbiotic organelles & their ancestors

• Both mitochondria and chloroplast have double membranes, which function to regulate the passage of materials into and out of the cell and to maintain a stable internal environment 

• Like [prokaryotic cells; mitochondria and chloroplasts 

  • Both have their own circular DNA encoding genetic information and can reproduce by a similar process used by prokaryotes 

  • Both contain their own ribosomes that synthesis proteins 

Key takeaway 

• Both prokaryotic and eukaryotic cells have external plasma membranes. However, whereas prokaryotes only have internal regions where specialized structures and function can occur (ex; nucleoid region containing DNA), eukaryotic cells have additional internal membrane-bound organelles that compartmentalize the cells 

• According to the theory of endosymbiosis a previously free-living prokaryote (bacteria) was engulfed by another cell through endocytosis. After living together symbiotically for some time, the once free living prokaryotic lost its independent functionality and gave rise to either the mitochondria or the chloroplasts