Mitochondrial Disease, Parkinsons - Research Paper Example

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Mitochondria are large organelles about 1 to 2 micrometer in diameter, upto 2000 of which are present in eukaryotic cells and constitute upto 25% of the cellular volume. The outer membrane enclosing the mitochondria is smooth, while the inner membrane is thrown into a series of folds known as the cristae. The space between the two membranes is called the intermembrane space. Both the structure and the quantity of mitochondria in different tissues can differ greatly depending upon the metabolic needs of the tissue. [Koolman et al 2005]
Mitochondria play several vital roles in the normal functioning of the cell. Their most important role is in the production of ATP by oxidative phosphorylation. They also serve as reservoirs of calcium within the cells and play a vital role in inducing apoptosis. . [Koolman et al 2005]
The vast range of mitochondrial functions are associated with a range of mitochondrial enzymes. "Pyruvate dehydrogenase, the TCA cycle, beta hydroxylation of fatty acids and parts of the urea cycle are located in the matrix. The respiratory chain, ATP synthesis and parts of the heme synthesis pathway are associated with the inner membrane." [Koolman et al 2005, pg 210]
One of the unique features of the mitochondria is that they are a self replicating organelle and can replicate independent of the parent cell. The mitochondrial genome is composed of 37 genes. Of these, "24 specify a mature RNA product, 22 molecular tRNA molecules and 2 molecular rRNA molecules. the remaining 13 genes encode polypeptides that are synthesized on the mitochondrial ribosomes [Strachan and Read 2004, pg 243]. Unlike nuclear DNA, mitochondrial DNA is very compact, lacking exons. For this reason any coding error in the mitochondrial DNA is far more likely to be transmitted to successive generations of the cell. However, because of the large number of mitochondria, the overall effect of such a mutation remains small unless transmitted in a gamete to the next generation. Mitochondrial DNA is exclusively maternal in origin being inherited from the egg, not the sperm. Thus the descendents of males affected by mitochondrial diseases are safe from inheriting the disease. The diseases can however affect men and women equally. [Passarge 2006]
Some common mitochondrial diseases include:
Lebers optic atrophy
MELAS (mitochondrial encephalopathy with lactic acidosis and stroke like episodes)
Kearns- Sayres syndrome
Some familial types of diabetes mellitus
Some forms of progressive nerve deafness and antibiotic associated deafness
MERRF (myoclonic epilepsy with ragged red fibres)
Pearson syndrome [Naviaux 2008]
Parkinsons disease is a degenerative disorder affecting the basal ganglia. It causes degeneration of the dopaminergic neurons in the substantia nigra, leading to decreased inhibition of the subthalamic nuclei and more active inhibition of the cortex. Its is characterized clinically by a triad of bradykinesia, tremor and rigidity. The exact cause for the development of parkinsonism has so far remained elusive. A syndrome very similar to parkinsonism is seen to develop in individuals who abuse methyl-phenyl tetra hydropyridine. This lends support to the theory that environmental factors are responsible for the causation of the disease. The current belief is that genetic and environmental factors both have a role to play. There are no diagnostic tests, and the condition is ...Download file to see next pagesRead More