Structure of mitochondria, Biology

STRUCTURE

Mitochondria is a double unit membranous structure. It consists of outer & inner membranes.


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  • Outer membrane is smooth & made up of lipoproteins. It bears many non stalked particles. These particles are known as subunits of parson. In outer membrane carrier protein is also present. Carrier protein is similar to bacterial porins (proteins), which is present in gram negative bacteria.
  • Outer membrane has more phospholipids (Phosphatidyl choline) and cholesterol as compared to inner membrane.
  • Inner membrane is selectively permeable in comparison to outer membrane. Many types of enzymes are present in inner membrane, which are involved in ATP synthesis (oxidative phosphorylation). Outer surface of inner membrane is called C- face while inner surface called M- face. Inner membrane is folded into a number of finger like cristae. Cristae are tubular finger like but in fungi cristae' are plate like while in Euglena cristae are vesicle shaped. Cristae word coined by Palade. Inner membrane have electron acceptors arranged in a definite sequence and form electron transport system (ETS). Inner membrane is studded with pin head particles called oxysomes or elementary particles or particles or subunits of Fernandez Moran. (104  to 106 in number). Each F particle consists of three parts - Basal plate, Stalk and Head. ATP synthesis occur in head region of oxysome because here ATPase enzyme is present. Synthesis of ATP in head region can be proved by sonication experiment. There is a factor at the base of oxysome that is called F which attach particles to inner mitochondrial membrane. This factor also termed as Oligomycin Sensitivity Conferring Protein (OSCP) Oxysomes composed of ATPase enzymes and concerned with Oxidative phosphorylation (Recker 1967).

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  • Unit of mitochondria = Oxysomes.
  • Unit of ATP synthesis = Oxysomes
  • Inner membrane have less phospholipids. Phospholipid in inner membrane is mainly diphosphatidyl glycerole.
  • Each membrane has thickness of 60-75 Å Both membrane separated by a outer chamber or perimitochondrial space (80-100Å). This space is rich in coenzymes and enzymes required for oxidation of fats.
  • Inner chamber enclosed by inner membrane which consists of matrix. Mitrochondrial matrix have 70% of total cell enzymes, which are involved in Kreb's cycle. Beside these enzymes matrix have a complete protein synthesis apparatus. Matrix contains mtDNA, RNA and ribosomes.

mtDNA is circular or double stranded. It has :-

1. High G-C content

2. High melting point

3. High renaturation temperature

4. It can replicate itself during any stage of cell division (from G-2 to cytokinesis)

5. 2-6 copies present in each mitochondria.

6. Mitochondrial DNA can code the synthesis of 10 different types of proteins ( Membrane proteins). Rest of the proteins and enzymes of mitochondria are synthesized under the control of nuclear genes.

7. Mitochondrial DNA was discovered by Nash and Margit (1963).

8. Enzymes for replication and transcription of DNA like DNA- polymerase and RNA polymerase.

  • In mitochondria 70s types ribosomes are present, which are known as mitoribosomes. (Mitochondria of mammals have 55s ribosomes)
  • In scurvy disease several mitochondria fuse to form large bodies called chondriosphere.
Posted Date: 10/5/2012 6:59:41 AM | Location : United States







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