A young girl has MELAS syndrome (Mitochondrial encephalomyopathy, lactic-acidosi
ID: 212128 • Letter: A
Question
A young girl has MELAS syndrome (Mitochondrial encephalomyopathy, lactic-acidosis, and stroke-like episodes). This syndrome is due to a mutation in the gene encoding complex I of the electron transport chain. Describe the role of the electron transport chain in the synthesis of ATP. The young girl has extreme muscle weakness. Given the nature of the mutation in this inherited disorder, explain why the young girl has muscle weakness. The young girl is showing signs and symptoms that are common of metabolic acidosis due to a buildup of lactic acid in the blood. Given the nature of the mutation in this inherited disorder, explain why the young girl has lactic acidosis.Explanation / Answer
Electron transport chain located in the inner mitochondrial membrane of eukaryotes has a role in the formation of ATP by converting large amount of energy released during the oxidation of NADH and FADH2.
Most of the energy released during the oxidation of glucose to CO2 is stored in the reduced form of coenzyme ( NADH and FADH2) , generated during glcolysis and TCA cycle. Durind oxidation, electrons released from NADH and FADH2 passes through the series of electron carriers present in the electron transport chain to oxygen, which is reduced to water and the released during this process is used for the formation of ATP.
MELAS syndrome is cause by the point mutation, A-to-G transition at nucleotide 3243 of the mitochondrial DNA ( mtDNA). In lactic acidosis , accumulation of lactic acid occurs in the body which results in the extremely lowpH in the blood. this acid makes the body difficult to produce energy and this is the reason why muscles fell weakeness.
Lactic acidosis occurs due to point mutation in the E1 alpha-subunit of the pyruvate dehydrogenase multienzyme complex. The pyruvate dehydrogenase complex converts pyruvateinto acetyl-CoA which is essential to begin the series of chemical reactions that produce energy for cells. With loss of function of this complex, pyruvate builds up in the body and is converted to lactic acid. The excess lactic acid causes lactic acidosis in affected individuals. Additionally , the production of cellular energy is also reduced.
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