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.