Coupon Accepted Successfully!



These are relatively large, easily identifiable organelles found in all cells except in bacteria and blue-green algae. Some of the specialised cells like mature mammalian erythrocytes (RBC) are also devoid of mitochondria. These cellular organelles have been described as the ‘power house’ of the cell since their function is generation of energy through cell respiration, for all metabolic activities of the cell. These organelles were first observed by Kolliker in 1880. Later systematic observations were made by Altmann (1886) and the name mitochondria (Greek mitos=thread, chondrion=granule) was given by Benda (1897).

Under the light microscope, mitochondria appear as rod shaped filamentous structures in the majority of cells. They appear granular in spermatocytes and oocytes and club-shaped in liver cells. Their size and number show variations depending on the type of the cell as well as the metabolic activity of the cell.

Electron microscopic studies reveal a very characteristic structure of mitochondria. Each mitochondrion consists of a double membrane structure. The outer membrane is separated from the inner membrane by a space called perimitochondrial space. The inner membrane is produced into a large number of infolding membranes which are called cristae. The cristae are a characteristic feature of mitochondria. Enclosed in the inner membrane is the mitochondrial matrix. Very highly magnified electron micrographs show that the inner sides of the inner membrane are covered with tiny particles. Morphologically each particle appears to have a spherical head (F1 sub-unit) and an elongated stalk (F0 sub-unit).

The spherical head of each particle projects into the matrix from the membrane. The inner membrane particles are called elementary particles or oxysomes. The ultra structure of mitochondria shows variations in different types of cells, at different stages of development or in different physiological conditions.


Mitochondria - Structural Features

Functionally mitochondria are centres of cellular respiration and centres of production of energy-rich ATP molecules. It is these organelles that supply all the energy needed for the energy-consuming processes in the cell; hence they are aptly called the ‘power houses’ of the cell. The production of energy in the cell is through a process of oxidation of various constituents of the food materials namely carbohydrates, proteins and lipids. It has been shown that mitochondria contain all the enzymes needed for the process of oxidative phosphorylation by which the energy-rich ATP molecules are synthesized from ADP and phosphoric acid. It has been found that when cells are removed from aerobic (presence of oxygen) conditions to anaerobic conditions (absence of oxygen) the tricarboxylic acid cycle (TCA cycle) stops, mitochondria disappear and a remarkable type of endoplasmic reticulum develops instead. Thus in anaerobic conditions not only is oxygen absent but mitochondria are also absent from the cell.

The enzymes of the TCA cycle are found in a series on the inner membrane of mitochondria. The enzymes of the cytochrome system occur in the inner membrane particles or oxisomes. It is clear that there is a need for precise correlation and coordination in the function of many enzymes to bring about the process of oxidative phosphorylation, by which energy is packed in high-energy phosphate bonds of ATP. The presence of the enzyme ATPase, which brings about the linking of phosphates to ADP molecule, in the inner membrane particles of mitochondria suggests that the final step of phosphorylation occurs in these particles.


Test Your Skills Now!
Take a Quiz now
Reviewer Name