The existence of mitochondria as cytoplasmic particles was observed by Kalliker, Fleming and Altman, but the name mitochondrion was given by C. Benda (1897). Mitochondria, is a Greek word derived from mitos=filament and chondros= granules. They have been variously called bioplast, chondriosomes, chondriomes, chondrioconts etc. They are of universal occurrence in every living cell except that of prokaryotes.
The shape of mitochondria is variable. Occasionally their shape is influenced by environment and physiological conditions. However, they may be granular, club shaped, tennis racket shaped, vesicular or rod shaped. Like shape the size also varies. The rod shaped mitochondrion are 0.5m to 2m but may attain a maximum length of 7m. The mitochondrion in general show uniform distribution and orientation but are characteristic to species in question. The number of mitochondria per cell also varies, e.g., in the cell of rat liver, 500, 1000 and sometimes 2500 mitochondria per cell have been reported. In Sea Urchin, the number varies between 14,000 to 1,50,000 per cell.
Structure
A typical mitochondria is a sausage shaped body, 1.5m long and 5m in diameter. Electron microscopy reveals that it is made up of two-unit lipoproteinaceous membrane lying parallel to one another. The outer membrane appears to be smooth or finally sculptured but the inner membrane form involutions inside the lumen, which are called cristae or cristae mitohondrials. These cristae are delicate and finger shaped and may be branched or unbranched. On the outer surface of outer membrane an inner surface of inner membrane are found numerous minute structures called oxysomes or F1 particles. The oxysomes on the outer surface are simple, globular, but those on the inner surface have a stalk and bacteriophage like head. The stalk is hollow, 30-35AO in width and 45-50 AO long, whereas the head is 75-80 AO in diameter. Oxysomes are proteinaceous in nature and have been variously named as elementary particles, inner lamellae spheres, F1 particles etc. The cavity of mitochondrion is occupied by homogenous and finely granular mitochondrial matrix.
Chemically mitochondrion consists mainly of proteins (65-70%), lipids (25-30%), RNA (0.5%) and DNA. The outer membrane fraction has 40% lipid content, while inner membrane has only 20% lipid content. Enzymes constitute about 30% of total protein. Mitochondria are rich in manganese. Only 70s types ribosome�s are found in mitochondria.
Besides these variety of vitamins and enzymes of krebs cycle are found situated on the surface of elementary particles or in stroma. Enzyme of ETS chain are found as constitutents of inner membrane.
Function of Mitochondria
1. Christian de Duve called mitochondria has power
2. Christian de Duve called mitochondria as powerhouse of the cell as these are source of supply to readily available from of energy to be used in various activities. The energy is in the form of ATP.
3. In mitochondria, the ATP molecules are formed during aerobic respiration (Krebs cycle). In it F0-F1 combination function as ATP synthase that catalyses ATP formation.
4. The chemical reactions of Krebs cycle take place in the matrix of mitochindria, where in also, 2ATP molecules per glucose molecule oxidation are also formed in GTP mills.
