Viewing mitochondria

Mitochondria can be isolated by cell fractionation brought about by differential centrifugation. Homogeneous fractions of mitochondria can be obtained from liver, skeletal muscle, heart, and some other tissues. They can be observed easily in cells cultured in vitro, particularly under darkfield illumination and phase contrast microscope. Janus green stains living mitochondria greenish blue due to its action with cytochrome oxidase system present in the mitochondria. This system maintains the vital dye in its oxidized state. In the surrounding cytoplasm the stain is reduced to a colourless base. Fluorescent dyes (rhodamine 123), which are more sensitive, have been used in isolated mitochondria and intact cultured cells. Such stains are more suitable for in situ metabolic studies of mitochondria. Different parts of mitochondria have distinct marker enzymes for histochemical markings, such as cytochrome oxidase for inner membrane, monoamine oxidase for outer membrane, malate dehydrogenase for matrix and adenylate kinase for outer chamber.

Function of mitochondria

• The most important function of the mitochondria is to produce energy. The food that we eat is broken into simpler molecules like carbohydrates, fats, etc., in our bodies. These are sent to the mitochondrion where they are further processed to produce charged molecules that combine with oxygen and produce ATP molecules. This entire process is known as oxidative phosphorylation.
• It is important to maintain proper concentration of calcium ions within the various compartments of the cell. Mitochondria help the cells to achieve this goal by serving as storage tanks of calcium ions.
• Mitochondria help in the building of certain parts of the blood, and hormones like testosterone and estrogen.
• Mitochondria in the liver cells have enzymes that detoxify ammonia.

Although most of the genetic material of a cell is contained within the nucleus, the mitochondria have their own DNA. They have their own machinery for protein synthesis and reproduce by the process of fission like bacteria do. Due to their independence from the nuclear DNA and similarities with bacteria, it is believed that mitochondria have originated from bacteria by endosymbiosis.

 

Interesting Facts

• The endosymbiotic relationship of mitochondria with their host cells was popularized by Lynn Margulis.
• Mitochondria and chloroplast follow maternal inheritance.

• Some of the diseases caused by defective mitochondria are: Diabetes mellitus and deafness (DAD), Leber's hereditary optic neuropathy and Leigh syndrome.

• A few groups of unicellular eukaryotes lack mitochondria: the microsporidians, metamonads, and archamoebae.