All aerobic cells of plants and animals contain mitochondria with the exception of bacteria and blue-green algae. Mitochondria were first observed by Kolliker in 1880 and later Flemming (1882) and Altmann (1890) have confirmed the presence of mitochondriá . mitochondriá have uniform distribution in cell. The number of mitochondria per cell varies from species to species. and from cell to cell depending upon the functional state of the cell. While some algae contain one mitochondrion per cell, an amoeba contains 50,000 mitochondria. Usually mitochondriá are 1 to 4 micron long and 0.2 to 0.1 micron broad.
Structure, function and biogenesis of Mitochondria are give below:-
Structure of Mitochondria:
Mitochondria can be seen under light microscope as filamentous, spherical or sausageshaped structure. Only under electron microscope ultrastructure of mitochondriá can be seen. Each mitochondrion is enclosed by two membranes. The outer membrane is separated from the inner membrane by a space of 60 A° to 100 A°. The inner membrane is extended into folds or cristae which project like fingers into the inner space of the mitochondrion. Inside the mitochondrion a dense, homogeneous matrix called mitochondrial matrix is found.
The inner and outer membrane are trilaminer in nature. Each of the membrane is composed of an outer and an inner layer consisting of protein molecules. The inner layer is composed of bimolecular layer of lipids. The inner membrane also contains some racket like bodies attached to it by short stem. These are called F1 particles or elementary particles. These particles represent ATPase. Mitochondria contain 25-30 per cent lipid, 5-7 per cent RNA and traces of DNA and 60-70 per cent protein. Nearly 60 different types of enzymes are found in mitochondriá .
Facts about Mitochondria:
Occurrence : Present in all eukaryotic cells except mature mammalian RBC.
Special, oval, sausage, fibrillar or granular.
Average size 2-6 micro meter.
Variable, Depend upon the metabolic state of the cell. More mitochondria are found
in young cells. germinating seeds and animal cells. All the mitochondriá of a cell are collectively called chondriosomes.
There are two membranes. such 60A° thick, lipoproteinous and trilaminar. The outer membrane is permeable. While the inner one is semipermeable. The inner membrane produces inward folds called cristae. The outer surface of the cristae bears a number of knob-like structures called elementary-particle or inner membrane spheres or oxysomes. It consists of a head piece or F1 sub-unit and a stalk joint to the base piece or subunit. It also contains all the enzymes of electron transport chain, the most notable one is ATPase which is concerned with ATP synthesis.
Mitochondrial chamber :
There are two chambers. The outer chamber lies between two membranes. It is filled with water, minerals and enzymes. The inner chamber lies inside which is filled up by mitochondrial matrix.
Semi-antonomous nature :
Mitochondria can self-duplicate, can synthesise some types of Protein, produce energy and hence they are called semi-autonomous system.
Function of mitochondria:
(1) Mitochondria are the sites of aerobic respiration. mitochondriá are also the ‘powerhouse’ of the cell. They generate energy for an vital activities of the cell. They produce energy rich ATP molecules from food, oxygen and ADP. The process involves a number of complex biochemical reactions. mitochondriá perform oxidation, dehydrogenation and oxidative phosphorylation. They are actually the respiratory organs of the cells where food is oxidised to CO2 and H2O and a large amount of energy is released for synthesis of ATP. This process is called oxidative phosphorylation which constitutes an important step in respiration process of aerobic organisms. The respiratory chain and oxidative phosphorylation involves a cyclic process called Kreb cycle or Citric acid cycle of the respiration process which entirely takes places within the matrix of the mitochondria.
(2) Help synthesis of cytochromes, steroids, some amino acids.
(3) Regulate calcium ion concentration of the cell.
Biogenesis of Mitochondria:
Mitochondria develop from pre-existing mitochondriá by division. Presence of DNA and ribosomes support this view. However, the biochemical activities and hereditary materials of the cell determine their number, size and activities.