Key Knowledge:
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Mitochondria are the 'power plants’ of the cell – synthesising large amounts of ATP via aerobic respiration
- All eukaryotic cells possess mitochondria – aerobic prokaryotes use the cell membrane to perform oxidative phosphorylation
Structure
The structure of a mitochondrion is adapted to the function it performs:
- The mitochondrion is a double membrane structure with the inner membrane arranged into folds (cristae) to increase the SA:Vol ratio
- The inner membrane contains the electron transport chain and ATP synthase (which is used for oxidative phosphorylation)
- The gap between the membranes (intermembrane space) is very small to maximise the gradient upon proton accumulation
- The internal fluid is called the matrix and contains the enzymes responsible for the Krebs cycle
Mitochondria evolved via endosymbiosis and hence retain structural characteristics consistent with an independent prokaryotic origin
- They have a double membrane structure (due to vesicular coating as part of the process of endocytosis)
- They have their own DNA (circular and naked), 70S ribosomes and their metabolic processes are susceptible to certain antibiotics
Micrographs
Typically, mitochondrial diagrams should display the following features:
- Usually sausage-shaped in appearance (though will appear more rounded in perpendicular cross-sections)
- Inner membrane contains many internal protrusions (cristae)
- Intermembrane space is very small (allows for a more rapid generation of a proton motive force)
- Ribosomes and mitochondrial DNA are usually not visible at standard resolutions and magnifications
Note: Electron micrographs of a mitochondrion may differ in appearance depending on where the cross-section occurs
