Mitochondria

Historical

They were first observed by Kolliker, 1880 in striated muscles and called them Sarcosomes, but the credit of discovery is generally given to Flemming, 1882 and Altmann, 1894. While Flemming called them filia, Altmann named them as bioplast. The term mitochondria was introduced by Benda, 1897. Meeves, 1904 was first to observe them in plants (Nymphaea), Michaelis, 1898 demonstrated their role in respiration. Bensley and Hoerr, 1934 isolated them from the liver cells. In prokaryotes, the mitochondria are absent. Here, the specialised folded plasma membrane called Mesosome contains respiratory enzymes and performs all the respiratory functions. Thus, it is analogous to mitochondria of eukaryotes. Mitochondria are cell organelles of aerobic eukaryotes which take part in oxidative phosphorylation and Krebs cycle of aerobic respiration. They are called power houses of cell because they are the major centres of release of energy in the aerobic respiration.

Number

Mitochondria are sec­ondarily lost in the red blood corpuscles of mammals. Their number varies from one in some algae (e.g., Microasterias, Chlorella), 25 in a sperm cell, 300—400 in a kidney cell, 500— 1000 in liver ceil, 30,000 in some oocytes, 50,000 in giant amoeba named Chaos chaos and 500,000 in flight muscle cells. The number depends upon cellular activities. Cells of dormant seeds have very few mitochondria. Those of germinating seeds have several mitochondria; in general green plant cells contain less number of mitochondria as compared to nongreen plant cells and animal cells.

Position

The position of mitochondria in a cell depends upon the requirement of energy and amino acids. In unspecialised cells they are randomly distributed throughout the cytoplasm. In absorp­tive and secretory cells, they lie in the peripheral cytoplasm. During nuclear division, more of mitochondria come to lie around the spindle. Mitochondria are more abundant at the bases of cilia or flagella to provide them energy for movements. In muscle fibers they occur in rows in the regions of light bands in Between the contractile elements. The mitochondrial system of a cell is called chondriome. When they degenerate, due to fusion they form clusters, called chondrospheres

 Shape and Size

Mitochondria differ in shape like spherical (e.g., Yeast), cylindrical, sausage-shaped, tubular or filamentous. In Chlorella the single mitochondrion is tubular and branched. The shape is also controlled by physiological conditions of the cells. Commonly mitochondria are cylindrical in outline. Like shape, the size of mitochondria is also variable. Normally, they have a length of 5—10 um and a diameter of 0.5 um.

 Ultrastructure

The mitochondria are bound by double unit membrane where each membrane is 60 A0 thick. The two membranes are separated by 40 - 70 A0 wide perimitochondrial space or outer chamber. When they are treated with detergents like digitonin or lubrol, their outer unit membrane is removed and what is left behind is called as mitoplast. The space bound by inner unit membrane is called inner membrane space which is filled by a matrix. The side of inner membrane facing outer (intermembrane) chamber is called C-side i.id the side facing inner chamber is called M-side. The inner unit membrane is folded to form the cristae or tubules (also called microvilli) or vesicles. Accordingly, we can differentiate three types of mitochondria as under:

(a)    Cristae type: They are generally found in animals.

(b)    Tubule type: They are found in plants.

(c)    Intermediate type: They too are found in plants.

The outer surface of outer membrane and inner surface of inner membrane are supposed to be covered with thousands of small particles. Those on the outer membrane are stalkless and called Subunits of Parson. The inner membrane particles have stalk and are called Subunits of 

Fernandez Moran. (But according to recent views and Electron Microscopic studies, the outer membrane is almost smooth.)

Outer Membrane:

The membrane is smooth. It is permeable to a number of metabolites. Because of it, some workers think that the membrane possesses minute pores. A few enzymes are located in the membrane. It is poorer in proteins as compared to inner membrane.

Inner Chamber:

It forms the core of the mitochondrion. The inner chamber contains a semi­ fluid matrix. The matrix has protein particles, ribosomes, RNA, DNA (mitochondrial or mDNA), enzymes of Krebs cycle, amino acid synthesis and fatty acid metabolism. Mitochondrial ribosomes are 55 S to 70 S in nature. They thus resemble the ribosomes of prokaryotes. DNA is naked. It is commonly circular but can be linear. DNA makes the mitochondrion semi-autonomous. Enzymes of electron transport are located in the inner mem­brane in contact with elementary particles.

Outer Mitochondrial Membrane

Inner Mitochondrial Membrane

1.   The membrane is smooth.

 

2.   It hears porins or protein lined channels.

 

3.   Foldings are absent.

4.  Protein content is roughly equal to that of lipids.

5. Cholesterol   and   other   lipids   are   present. Cardiolipins are absent

6.   Electron transport system is absent.

7.   It is permeable to most biochemicals.

1. The membrane contains a large number of       particles.

2. Porins are absent. Instead, carrier and other       transport proteins are present.

3.   Inner mitochondrial membrane develops a       large number of infoldings called cristae.

4.   Protein content is quite high (upto 80%)       while lipid content is low.

5.   Cardiolipins occur.

6. The membrane bears electron transport       system.

7. Inner mitochondrial membrane is selectively       permeable.

(Rest part of study materials after registration).

Details heading of rest part study materials:-

2. Cristae
3. Femandez-Moran particle
4. Oxysome details.
5. Five complex detail for ETS.
6. Matrix
7. Mitochondrial DNA.
8. Mitochondrial Genetic code.
9. The mitoapparatus for protein synthesis & RNA synthesis
10. Comparison between normal DNA & mitochondria DNA
11. Mitochondrial DNA complexity in different organisms
12. Chemical Composition
13. Respiratory proteins encoded in human mitogenes
14. ATP yield from complete oxidation of glucose.
15. Autonomy of Mitochondria
16. Mitochondrial disease
17. Import of proteins into mitochondria
18. Insertion of mitochondrial membrane proteins
19. Sorting proteins to the intermembrane space
20. Demonstration that the γ subunit of the F0 complex rotates relative to the (αβ) 3 hexamer in an energy-requiring step
21. The rotation of the bacterial flagellum driven by H+ flow
22. Function

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