MITOCHONDRIA

Mitochondria are commonly called as power house of the cell. They provide energy transuding system. This system is used to change the food into chemical energy by oxidative phosphorylation. ATP is synthesized during oxidative phosphorylation.

Discovery

Mitochondria were first described by Altmann in 1894. He named them as bioblasts. He predicted that bio blasts had some relation with oxidation reactions. Later. Banda changed their name to mitochondria in 1897. Hegeboom described in 1948 that mitochondria are involved in oxidation reduction reactions in cells. Location and number

Mitochondria have uniform distribution in cells. Sometimes, mitochondria concentrate near the nucleus. Some mitochondria are mobile. They reach the site where ATP is required. Some mitochondria are permanently fixed in cell. Mitochondria are grouped like rings in muscle cells. They have variable length up to 7pm. There are 1000 to 1600 mitochondria in liver cells. Some ocytes contain 300,000 mitochondria. Chloroplasts are also involved in ATP production in cells. Therefore, number of mitochondria is lesser in green cells.

Chemical nature of Mitochondria

The membranes of mitochondria are composed of lipid and proteins.

The outer membrane of mitochondria contains 40% lipids and 60% proteins and inner membrane contains 20% lipids and 80% protein. Thus the ratios of lipid/protein in the outer membrane is 2: 3 and inner membrane is I: 4. Outer membrane contains a large amount of cholesterol. Inner membrane contains electron acceptors of electron transport chain and many enzymes. So it has high contents of protein.

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Structure of mitochondria

Mitochondria are rod shaped. In some cases, mitochondria are filamentous, vesicular or granular. Their diameter is about 0.5pm. The mitochondria contain two membranes. These membranes are separated by 8 to 9nm. The membranes are composed of unit membrane structures. The unit membrane is composed of lipid and protein molecules. These membranes form two compartments.

(a)Inner compartment: It is filled with the mitochondria! matrix. It is bound by inner membrane.

(b)Outer compartment: It is present between the inner and outer membrane.

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Mitochondrial matrix

The mitochondria] matrix is generally homogenous fluid. But sometimes it contains dense granules. It appears gel like. These granules contain phospholipids. The mitochondria’ matrix also contains a circular DNA and ribosomes.

Mitochondria! crest

The mitochondria] matrix contains complex infolding. These infoldings are called mitochond;ial crests or cirstae. The mitochondrial crests are incomplete septa or ridges. The numbers of crests are variable in cells. Mitochondria of liver cells have few crests. But the muscular celk have abundant crests.

Fi Particles

The inner membrane of the mitochondria contains numerous small particles. These are called elementary or F1 particles. Their diameter is 8.5nm. They are regularly spaced at intervals of I Onm on the inner surface of the inner membrane. There may be 104 and i05 Fi particles per cell. These particles conta’a special ATPase complex and proton pump. This complex is involved in the coupling oxidation and phosphorylation.

Enzymes of mitochondria

(a)    Outer Membrane: Moloamine oxidase, NADH-Cytochrome reductase, Fatty acid CoA ligase.

(b)    Space between outer and inner membrane: Adenylate kinase,

nucleoside diphosphokinase.

(c)    Inner membrane: Respiratory chain enzyme. ATP synthase,

(d)    Matrix: Malate dehydrgenase, Citrate synthetase, a-keto acid dehydrgenase.

Functions of mitochondria

Following processes take place during oxidations reactions in

m itochondria:

I. Mitochondrial matrix: Krebs’s cycle and a-oxidation and 13- oxidations of fats. These reactions produce NADH and EADH.

  1. Inner membrane space: The electron carriers pump IT into the inner membrane space. High concentration of H. produces IT gradient.
  2. Inner membrane: Electron transport chain and ATP synthesis by oxidative phosphorylation.

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