Mitochondria (singular- mitochondrion) are the energy powerhouses of cells. Much of the energy that cells (and therefore individuals) require to function is harvested from biomolecules such as sugars and fats obtained from food. Mitochondria carry out the final steps of converting the food to energy. Like the nucleus, mitochondria are surrounded by a double membrane.
Like the burning of gasoline in an automobile engine, the energy production process is not completely efficient and produces by-products that often have undesirable effects. Energy production in mitochondria leads to the production of chemicals that may damage DNA and therefore cause genetic changes. These dangerous side products are thought to contribute to the mutations seen in cancer cells.
A diagram of a mitochondrion, showing the two separate membranes and the inner compartment that is the site of energy production is shown below.
In the image below, the mitochondria in mouse cells have been stained red. The nuclei and chromosomes of the cells are blue. Note the wide distribution, large number and the somewhat irregular shapes of the mitochondria. The green regions near the nucleus in each cell are organelles known as the golgi apparatus, they are involved in the modification and shipment of biomolecules such as proteins.
The image above was used with the permission of the copyright owner, Molecular Probes.