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Ethanol

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However, ethanol can replace sizable amounts of carbohydrates as an energy ... and the normal functioning of other metabolic pathways, such as gluconeogenesis. ... – PowerPoint PPT presentation

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Title: Ethanol


1
Ethanol
  • Ch.23.3b

2
Ethanol
  • Ethanol is not a carbohydrate, nor is it a
    precursor for the biosynthesis of carbohydrates.
  • However, ethanol can replace sizable amounts of
    carbohydrates as an energy source when large
    amounts are ingested.
  • It is present in the blood of most humans, being
    produced by intestinal flora.
  • People ingest ethanol in variable amounts in
    beverages and fermented fruits.
  • Ethanol is metabolized in the liver to acetate
    and adds to the caloric content of the diet.
  • Ethanol has an energy equivalent of 7 kcal/g.
  • 100 mL of table wine has ethanol corresponding to
    about 72 kcal.
  • A jigger of whiskey furnishes approximately 120
    kcal.

3
Ethanol continue
  • When ethanol is metabolized in the liver, alcohol
    dehydrogenase oxidizes it first to acetaldehyde.
  • CH3CH2OH NAD ? CH3CHO NADH H
  • The acetaldehyde is oxidized further to acetate.
  • CH3CHO NAD H2O ? CH3COO- NADH H
  • A small fraction of the alcohol may be oxidized
    by other systems
  • Cytochrome P450 oxidase (also involved in
    detoxification of many drugs)
  • Catalase
  • The acetate produced from ethanol largely escapes
    from the liver and is converted to acetyl CoA and
    then to carbon dioxide by the way of the Krebs
    cycle.
  • The acetyl that stays in the liver may act as a
    precursor for lipid biosynthesis.
  • A significant consequence of metabolism of
    ethanol in the liver is the twofold to threefold
    increase in the NADH/NAD ratio.
  • With higher concentrations of blood alcohol, the
    concentration of NADH remains high, and the
    availability of NAD drops and limits both the
    further oxidation of ethanol and the normal
    functioning of other metabolic pathways, such as
    gluconeogenesis.

4
Fatty liver
  • Chronic consumption of significant amounts of
    alcohol may lead to a fatty liver, in which the
    excess of triacylglyceride is deposited.
  • This is caused by several contributing factors
  • Reduced triacylglyceride secretion from the liver
  • Reduced rates of fatty acid oxidation
  • Increased rates of lipid biosynthesis
  • These processes are associated with the increased
    acetyl CoA and NADH/NAD ratio in the liver that
    results from ethanol oxidation.
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