Mitochondria

The Powerhouse Of The Cell

Mitochondria is 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 was first described by Altmann in 1894. He named them as bioblast. He predicted that bioblast 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 & Number:

Mitochondria has uniform distribution in cells. Sometimes, the 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 7 µm. there are 1000 to 1600 mitochondria in liver cells. Some oocytes 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% of lipids and 60% of proteins and inner membrane contains 20% of lipids and 80% of proteins. Thus, the ratio of lipid/protein in the outer membrane is 2 by 3 ratio and inner membrane is 1 by 4 ratio. 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 proteins.

Structure of Mitochondria:

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

Inner Compartment: It is filled with the mitochondrial matrix. It is bound by inner membrane.

Outer Compartment: It is present between the inner and outer membrane.

Mitochondrial Matrix:

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

Mitochondrial Crest:

The mitochondrial matrix contains complex infoldings. These infoldings are called mitochondrial crest. The mitochondrial crest is also named as cristae. 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 cells have abundant crests.

F1 Particles:

The inner membrane of the mitochondria contains numerous small particles. These are called elementary or F1 particles. Their diameter is 8.5 nm. They are regularly spaced at intervals of 10 nm. On the inner surface of the inner membrane. There may be 10⁴ and 10⁵ F1 particles per cell. These particles contain special ATPase complex and proton pump. This complex is involved in the coupling oxidation and phosphorylation.

Enzymes of Mitochondria:

Outer Membrane: Monoamine oxidase, NADH-Cytochrome reductase, Fatty acid CoA ligase.

Space Between Outer & Inner Membrane: Adenylate kinase, nucleoside diphosphokinase.

Inner Membrane: Respiratory chain enzyme, ATP synthase.

Matrix: malate dehydrogenase, Citrate synthetase, α-keto acid dehydrogenase.

Functions of Mitochondria:

The functions of mitochondria are as follow:

Mitochondria Matrix: Krebs’s cycle and α-oxidation and β-oxidations of fats. These reactions produce NADH and FADH.

Inner Membrane Space: The electron carriers pump H+ into the inner membrane space. High concentration of H+ produces H+ gradient.

Inner Membrane: In inner membrane Electron Transport Chain and ATP synthesis by oxidative phosphorylation takes place.