Mitochondria (cell biology)

● MITOCHONDRIA 》

1. Mitochondria (Gr. mitos, thread; chondrion, granule) are organelles found in the cytoplasm of plants and animals. 

2. Mesosome of prokaryotes (bacteria) is analogous to mitochondrion in eukaryotes. 

3 Mitochondria (sing. mitochondrion) were first seen by Köllicker in 1850 in muscles and he called them 'sarco- somes'.

4. Flemming (1882) described these organelles as 'filia'. 

5. Altmann (1890) observed these structures and named them "bioblasts'. 

6. Benda (1898) stained these organelles with crystal violet and renamed them 'mitochondria'. 

7. Michaelis (1900) used Janus Green B as a vital stain to observe mitochondria in living cells. 

8. Bensley and Hoerr (1934) isolated mitochondria for biochemical studies by differential centrifugation. Morphology 

9. The shape of mitochondria is highly variable, ranges from short rod-shape to elongated filamentous form. 

10. Mitochondria show variable shape , so it shows pleomor- phism. 

11. The size of mitochondria is variable, they generally measure about 0.6 to 2 µm in diameter. 

12. Mitochondria have an average length of 5 to 10 µm. 

13. Mitochondria are not found in prokaryotes and mature human red blood cells. 

14. The number of mitochondria varies from one cell type to another. 

15. The number correlates with the metabolic activity of the cell. 

16. Mitochondria will be found in abundance where there is a maximum activity in  the body. 

17. A small number of mitochondria generally indicates cells of low metabolic activity. 

18 A single mitochondrion is found in Microsterias, a unicell- ular green algae. 

19. Plant cells have fewer mitochondria than animal cells. 

● Ultrastructure 》

20. A mitochondrion is enclosed by a double membrane envelope composed of lipid and protein.

21. The two membranes are separated by a narrow fluid-filled space called the outer compartment. 

22. The outer membrane is smooth, it is more permeable to small molccules, contains some enzymes bul is poorer in proteins. 

23. The inner membrane surrounds a central cavity of matrix (inner compartment) filled with a fluid. 

24. Folds of inner wall of mitochondria are called cristae. 

25. Crista causes an increase in the total surface area. 

26. Crista bears subunits called oxysomes (elementary particles, F, particles, electron transport particles, inner membrane subunits or Fernandez Moran particles). 

27. Disruption of mitochondria yields membrane fragments which are able to synthesis ATP. 

28. Mitochondria contain electron transport systems aggre- gated into compact association. F, particle is connected by a cylindrical stalk to a base piece or Fo subunit. 

29. The Fo-F combination functions as ATP synthetase, an enzyme that catalyses ATP synthesis. 

30. In Fi particles of mitochondria, ATP is generated. 

● Chemical Composition 》

31. Chemically, mitochondria consist of protein 70% (dry weight) and lipids 25-30%. 

32. Of the lipid component, 90% is phospholipid and 10% carotenoids, cholesterol, vitamin E and other traces. 

33. Mitochondria contain 0.5% of RNA and traces of DNA. 

34. Mitochondrial DNA comprises about 1% of total cell DNA. 

35. Mitochondria contain enzymes for oxidation, phospho- rylation and electron transfer. 

36. Out of total enzymes present in the cell, mitochondria alone has 70%. 

37. Mitochondria are rich in respiratory catabolic enzymes. 

● Functions of Mitochondria 》

38. Mitochondrion is known as the 'power house of cell'; the energy is released in it through cellular respiration. Within the cell, the site of respiration is mitochondria. 

39. The organelles in which aerobic respiration occurs in a cell are mitochondria. 

40. Mitochondria are present in the aerobic organisms only. 

41. If a cell is living in an environment without oxygen, it necd OKygun os use not have mitochondria.

42. Mitochondria are considered as storehouse of energy of centres of energy liberation. 

43. In a cell, the energy in the form of ATP is formcd A mitochondria. 

44. A common and easily available source of energy in living cells is ATP. 

45. After respiration the conversion of energy is mainly in ue form of ATP. 

46. The cell organelle which has electron transport system mitochondrion.

47. Oxidative phosphorylation is the formation of ATP in jespiration. 

48. Within the cell, the site of respiration or oxidative phos- phorylation is mitochondria. 

49. The end product of glycolysis is pyruvic acid which enters mitochondria and takes part in Krebs' cycle in the mitochondrial matrix. 

50. Enzymes connected with Krebs' cycle are packed in mitochondria. 

● Samiautonomous Organelles 》

Mitochondrion contains one or two molecules of circular DNA (double helical) having a circumference of about 5 µm. Mitochondrial DNA contains more cytosine and guanine than in nuclear DNA. 

Mitochondrion also contains m-RNA and ribosomes and synthesize some of its own proteins. 

Autonomic genome system is present in both mitochondria and chloroplasts. 

Mitochondria and chloroplasts are believed to be bacterial endosymbionts of cells because they have their nucleic acids; their membranes resemble those of bacteria; they do not arise de novo.

The presence of DNA in mitochondria and chloroplasts supports the hypothesis that mitochondria and chloroplasts both originated as independent free living organisms.