DNA (mt DNA)is oftenusedto depict variation within populations as well as across
ID: 202482 • Letter: D
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DNA (mt DNA)is oftenusedto depict variation within populations as well as across species. Why is this so? Brain Pathol, 1995 Apr:5(2):125-33. Myoclonic epilepsy with ragged-red fibers (MERRE): an immunohistochemical study of the brain. Sparaco M1, Schon EA, DiMauro S, Bonilla E. Abstract Myoclonic epilepsy with ragged-red fibers (MERRF) is a maternally inherited disorder of oxidative phosphorylation due to specific point mutations within the mitochondrial tRNA(Lys) gene. Mitochondrial dysfunction in the central nervous system (CNS) of patients with MERRF cal tmanifestations of the disease. Antibodies against accounts for the neurologi subunits of complex I. IIl,IV and V of the respiratory chain were used to study the expression of these proteins in the frontal cortex, cerebellum and medulla from an autoptic case of MERRF. We found a selective decreased expression of subunit ll of cytochrome c oxidase (COX-II) in these regions, Immunohistochemical abnormalities were more widespread than the lesions described by traditional histopathological tecluiques and made possible an attempt of explanation for the neurological symptoms of the patient. Draw a pedigree to show how MERRF is inherited. Why is it matermally inherited? How do you think a decreased expression of COX-II is related to the symptoms and why?Explanation / Answer
MERRF is a mitochondrial disorder caused due to point mutations within mitochondrial tRNA-Lys ligase.Mitochondria in the developing embryo is contributed by the ovum and not from the sperm cell, mitochondria from the sperm cell are not incorporated into the embryo. Hence children inherits mitochondrial DNA related disorders only from their mothers and an affected mother can transmit this disorder to all of her children and their will be no father to children transmission.
COX-II assembls with other COX subunits to form Complex IV of the electron transport chain in mitochondria which is crucial for synthesis of ATP. Since muscle cells and nerve cells have high energy needs and decreased levels of COX-II can lead to decrease in energy reserves of the cell thereby shutting down cellular processes in myocytes and neurons. This results in symptoms such as dementia, attaxia, neuropathy and myopathy. Abnormal mitochondria also acculmulates below the plasma membrane of the muscle fiber causing its boundary to become irregular and appear Ragged.
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