Mitochondria Mitochondria are the “power-house” of the cells. They perform oxidative phosphorylation for production of energy and able to synthesize lipid. Mitochondria are able to multiply; they possess their own DNA for self-replication.

General features They are rod-shaped organelle ranges from 2 to 6 μm in length and about 0.2 μm in width. Their size is nearly equal to that of the bacterial cell. 1- It is the source of energy for cellular activities. Via oxidative phosphorylation they produce ATP molecules (storage form of energy). 2- By electron microscope mitochondria are divided into two types: Cristae- type and tubular- type .

cristae-type mitochondria

tubular mitochondria

3- Number of mitochondria increases or decreases within the cell according to the cellular activity; their number increases in highly active liver and muscle cell. There are about 2000 mitochondria in hepatocyte. 4- Mitochondria are self-replicating organelles. They can grow and divide because they have a circular molecule of DNA.

5- Their mutation can lead to diseases such as: 6- Young-adult blindness. 7- Progressive muscular disorders. 8- Some cases of Alzheimer’s disease. 9- Type -two diabetes mellitus.

Structure of mitochondria 1. Smooth outer membrane. 2. Folded inner membrane. The folds form cristae and tubules. 3. Intermembrane space (10 – 20 nm) 4. Matrix that part enclosed by the inner membrane (intercristal space).

Outer Mitochondrial Membrane It is smooth and separated from inner membrane by Intermembrane space. Contact sites formed of carrier proteins between inner and outer membranes which act as pathway for proteins and small molecules from cytoplasm into the matrix

Inner Mitochondrial Membrane It is characterized by presence of large number of porins; a channel protein permeable to ions and metabolites that are required by mitochondria.

1- It contains complexes - I, II, III, IV, V 1- It contains complexes - I, II, III, IV, V. which carry out oxidative phosphorylation which in turn generates ATP. These complexes I, II, III, IV form the respiratory chain. 2- It contains also complex - V (the ATP –synthetase) which carries out ATP – synthesis . 3- The inner membrane folds to form cristae or tubules which increase the surface area for ATP – synthesis and the respiratory chain. 4- It contains high concentrations of phospholipid that makes it nearly impermeable to ions, electrons and protons for isolation of the matrix from intermembrane space.

ATP –Synthetases (Complex - V): They are Knob-like repeating units on the inner membrane which project from the inner membrane toward the matrix. They carry enzyme complex that store the energy in form of ATP molecules which are synthesized from ADP and inorganic phosphate.

Mitochondrial Matrix (Inter-cristal Space) The matrix of mitochondrion is filled with dense fluid which is formed of fine granular substance as observed under electron microscope. 1- About 50% of the matrix content is formed of proteins; enzymes that are responsible for: a) Degradation of fatty acids and pyruvate to acetyl Co– enzyme A. b) Oxidation of Acetyl Co-enzyme A in Krebs cycle. c) Synthesis of mitochondrial ribosomes, tRNA and mRNA by DNA transcription.  

Circular mitochondrial DNA in matrix and the enzymes are necessary for expression of mitochondrial genome.   2- Mitochondrial matrix contains also mitochondrial dense granules which are salts of calcium and magnesium.

Mitochondrial abnormalities Mitochondrial abnormalities: Mitochondrial DNA can be abnormal .This interferes with mitochondrial and cell functions , resulting in disorders referred to as mitochondrial cytopathy syndromes. The features (which differ in intensity from patient to patient ) include muscle weakness, degenerative lesions in the brain , and high levels of lactic acid.

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