Biochemistry: The Molecular Basis of Life
6th Edition
ISBN: 9780190209896
Author: Trudy McKee, James R. McKee
Publisher: Oxford University Press
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Chapter 9, Problem 7Q
Summary Introduction
To review:
The reason for the occurrence of lactic aciduria.
Introduction:
Pyruvate carboxylase deficiency (PCD) is a disease in which the enzyme pyruvate carboxylase is defective or nonfunctional. The main function of this enzyme is to produce oxaloacetate from pyruvate. An individual with nonfunctional PCD urinates high levels of lactic acid. This is known as lactic aciduria.
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One consequence of ethanol addiction is fatty liver disease, an illness in which liver cells accumulate large amounts of triacylglycerols, the esters derived from glycerol and fatty acids. Ethanol is oxidized in the cytoplasm of liver cells by alcohol dehydrogenase and aldehyde dehydrogenase to yield acetate and 2 NADH. Acetate is then transported into the mitochondrion, where it is converted to acetyl-CoA and metabolized in the citric acid cycle. When alcohol is consumed in excessive quantities, the resulting high levels of NADH cause metabolic abnormalities, one of which is high levels of fatty acid synthesis. Fatty acid synthesis, also a cytoplasmic process, uses acetyl-CoA as a substrate and NADPH as a reducing agent. Speculate about how a high level of cytoplasmic NADH provides a source of NADPH for fatty acid synthesis.
The glycerol derived from lipolysis of triacylglycerols is converted into glyceraldehyde 3-phosphate, which then enters into step 6 of the glycolysis pathway. What further transformations are necessary to convert glyceraldehyde 3-phosphate into pyruvate?
Leigh syndrome is characterized by psychomotor regression: that is, the progressive loss of mental andmovement abilities. Patients also suffer from lacticacidosis, a condition in which mitochondrial respiration is deficient, so their tissues metabolize glucoseanaerobically, leading to the buildup of lactate. Somepatients with Leigh syndrome have a mutation in themitochondrial gene MT-CO3, which encodes a subunit of the electron transport complex cytochromec oxidase. Other patients diagnosed with Leigh syndrome have a loss-of-function mutation in the nucleargene SURF1, which encodes a factor needed for theassembly of this same enzyme complex.a. How can the same symptoms result from mutationsin a mitochondrial gene and from mutations in anuclear gene?
Chapter 9 Solutions
Biochemistry: The Molecular Basis of Life
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- Which of the following is NOT a component of the pyruvate dehydrogenase complex? a. dihydrolipoyl dehydrogenase b. dihydrolipoyl transacetylase c. pyruvate dehydrogenase d. dihydrolipoyl catalasearrow_forwardWhich of the following is NOT a metabolic fate of pyruvate? The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate to form acetyl-CoA. Pyruvate carboxylase catalyzes the carboxylation of pyruvate to form oxaloacetate. Pyruvate kinase catalyzes the formation of phosphoenolpyruvate from pyruvate. Lactate dehydrogenase catalyzes the formation of lactate from pyruvate.arrow_forwardThe consumption of alcohol (ethanol), especially after periods of strenuous activity or after not eating for several hours, results in a deficiency of glucose in the blood, a condition known as hypoglycemia. The first step in the metabolism of ethanol by the liver is oxidation to acetaldehyde, catalyzedby liver alcohol dehydrogenase: Explain how this reaction inhibits the transformation of lactate to pyruvate. Why does this lead to hypoglycemia?arrow_forward
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