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How does the outer mitochondrial membrane differ from the inner mitochondrial membrane?
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mitochondrion
Mitochondria (red) are found throughout the cytoplasm of almost all eukaryotic cells (cell nucleus is shown in blue; cytoskeleton is shown in yellow).
The outer and inner mitochondrial membranes differ significantly in their structure and permeability, reflecting their distinct roles in cellular energy production:
- Permeability: The outer membrane is freely permeable to small molecules and contains specialized channels that allow for the transport of larger molecules. In contrast, the inner membrane is highly impermeable, preventing the passage of even small ions, which allows the organelle to maintain a specific chemical environment within the matrix.123
- Structure: The inner membrane is elaborately folded into structures known as cristae, which dramatically increase its surface area. The outer membrane does not exhibit these folds.312
- Function: The inner membrane is the primary site for the electron transport chain and the enzymes responsible for ATP synthesis. These processes rely on the inner membrane's ability to maintain an electrical potential and a proton gradient across its surface. Because it is actively involved in these metabolic processes, the inner membrane contains a very high proportion of protein—up to 75 percent of its composition.124