Cell Biology: Cellular Compartments Part III

MITOCHONDRIA AND CHLOROPLASTS

• Overview of Mitochondria source
• Main site of ATP production during aerobic metabolism are very large in size
• Outer membrane is about half lipid and half protein, contains porins that render the membrane permeable to molecules having molecular weights as high as 10,000 (a similar membrane to that of gram-negative bacteria)

• The inner membrane is less permeable is 80%protein, 20% lipid and forms cristae, or infoldings, that protrude into the matrix
• Degrades glucose to CO2 and H2O to produce 28 molecules of ATP (2 more molecules of ATP are produced in the cytosol)
• Overview of Chloroplasts source
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• Carry out photosynthesis
  
• Are surrounded by a double membrane and contain a network of internal membrane-bounded sacs

• Biogenesis of Mitochondria and Chloroplasts
  
• Grow by the incorporation of cellular proteins and lipids, and new organelles form by division of preexisting organelles - both processes occurring continuously during the interphase period of the cell cycle
• Evolution source
  
• Hypothesis that mitochondria and chloroplasts arose by the incorporation of bacteria into ancestral eukaryotic cells, forming endosymbiotic organelles
• Endocytosis of a bacterium by an ancestral eukaryotic cell would generate an organelle with two membranes, the outer membrane derived from the eukaryotic plasma membranes and the inner one from the bacterial membrane
• The F1 subunit of ATP synthase, localized to the cytosolic face of the bacterial membrane, would then face the matrix of the evolving mitochondrion or chloroplast membrane, such as occurs during development of chloroplasts in contemporary plants, would generate the thylakoid vesicles with the F1 subunit remaining on the cytosolic face, facing the chlorplast stroma
  
• Share with bacteria many proteins of similar sequences, including some involved in membrane translocation