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What Percentage Of A Triglyceride Molecule Cannot Be Converted To Glucose At All?

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Carbohydrate, Protein And Lipid Metabolism Notes

Part 1 – Metabolism Concepts and Measurement Carbohydrates, protein and fat are macronutrients. In the human body metabolism is the oxidization of carbohydrates, protein and fat to give CO2, H2O and energy. What is Metabolic Rate? Metabolic Rate is the amount of energy liberated per unit time. The Basal Metabolic Rate is the rate of energy expenditure at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The Basal Metabolic Rate is the largest component of total caloric expenditure in humans: 70% Physical activity contributes: 20% Thermogenesis & digestion contributes: 10% Units used for Metabolic Energy calorie (cal – note lowercase) is the standard unit of metabolic heat energy, being the amount of energy needed to raise 1g of water by 1 degree, from 15o to 16o C. Calorie (kilocalorie, kcal, big calorie, large calorie, kilogram calorie) is more commonly used, representing 1000 calorie. Joule is the SI unit for energy, such that 1 calorie = 4.2 joule. To convert from Calories (kilocalories) to kilojoules, multiply by 4.2. How do we measure Metabolic Ene Continue reading >>

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Popular Questions

  1. Christian

    I read conflicting views about whether or not the human body can create glucose out of fat. Can it?

  2. David

    Only about 5–6% of triglyceride (fat) can be converted to glucose in humans.
    This is because triglyceride is made up of one 3-carbon glycerol molecule and three 16- or 18-carbon fatty acids. The glycerol (3/51-to-57 = 5.2–5.9%) can be converted to glucose in the liver by gluconeogenesis (after conversion to dihydroxyacetone phosphate).
    The fatty acid chains, however, are oxidized to acetyl-CoA, which cannot be converted to glucose in humans. Acetyl-CoA is a source of ATP when oxidized in the tricarboxylic acid cycle, but the carbon goes to carbon dioxide. (The molecule of oxaloacetate produced in the cycle only balances the one acetyl-CoA condenses with to enter the cycle, and so cannot be tapped off to gluconeogenesis.)
    So triglyceride is a poor source of glucose in starvation, and that is not its primary function. Some Acetyl-CoA is converted to ketone bodies (acetoacetate and β-hydroxybutyrate) in starvation, which can replace part — but not all — of the brain’s requirement for glucose.
    Plants and some bacteria can convert fatty acids to glucose because they possess the glyoxylate shunt enzymes that allow two molecules of Acetyl-CoA to be converted into malate and then oxaloacetate. This is generally lacking in mammals, although it has been reported in hibernating animals (thanks to @Roland for the last piece of info).

  3. blu potatos

    To be more detailed it is the irreversibly of the reaction carried by Pyruvate dehydrogenase that makes the conversion of the fatty acid chains to glucose impossible. The fatty acids chains are converted to acetyl-CoA.
    Acetyl-CoA to be converted into pyruvate need an enzyme that can do the Pyruvate Dehydrogenase's inverse reaction (in humans there is no such enzyme). Than the pyruvete inside the mitochondria is converted into glucose(gluconeogenesis).

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