ninja icon


•  The structure of the mitochondrion is adapted to the function it performs

Mitochondria are the ‘powerplants’ 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

Mitochondria are thought to have once been independent prokaryotes that were internalised by eukaryotes via endosymbiosis

  • They have a double membrane structure (due to vesicular coating as part of the endocytotic process)
  • They have their own DNA (circular and naked) and ribosomes (70S)
  • Their metabolic processes are susceptible to certain antibiotics

The structure of the mitochondrion is adapted to the function it performs:

  • Outer membrane – the outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol
  • Inner membrane – contains the electron transport chain and ATP synthase (used for oxidative phosphorylation) 
  • Cristae – the inner membrane is arranged into folds (cristae) that increase the SA:Vol ratio (more available surface)
  • Intermembrane space – small space between membranes maximises hydrogen gradient upon proton accumulation
  • Matrix – central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur

Structure and Function of a Mitochondrion


ninja icon


•  Annotation of a diagram of a mitochondrion to indicate the adaptations to its function

Electron micrographs of a mitochondrion may differ in appearance depending on where the cross-section occurs

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

Mitochondrion Diagrams

My Image 1 My Image 2

  Click on the diagram to show / hide labels

ninja icon


•  Electron tomography used to produce images of active mitochondria

Electron tomography is a technique by which the 3-dimensional internal structure of a sample can be modelled

  • Samples are repeatedly imaged using a transmission electron microscope
  • Following each image, the sample is tilted to a different angle relative to the electron beam
  • The images are then compiled and used to computationally reconstruct a 3-D representation (called a tomogram)

When dealing with biological materials, samples are first prepared by either fixing and dehydrating or freezing (cryogenics)

  • This stabilises the biological structures and prevents aqueous contents (i.e. water) from expanding and exploding

Using electron tomography, the following features of active mitochondria have been identified:

  • The cristae are continuous with the internal mitochondrial membrane
  • The intermembrane space is of a consistent width thoughout the entire mitochondrion
  • The relative shape, position and volume of the cristae can change in active mitochondria

Overview of Electron Tomography