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Can Fatty Acids Can Be Converted To Glucose?

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In Silico Evidence For Gluconeogenesis From Fatty Acids In Humans

In Silico Evidence for Gluconeogenesis from Fatty Acids in Humans 2Systems Biology/Bioinformatics Group, Leibniz Institute for Natural Product Research and Infection Biology Hans Knll Institute, Jena, Germany 3Department of Human Nutrition, Institute of Nutrition, University of Jena, Jena, Germany 4Department of Clinical Nutrition, German Institute of Human Nutrition, Potsdam-Rehbrcke, Nuthetal, Germany 1Department of Bioinformatics, School of Biology and Pharmaceutics, Friedrich Schiller University of Jena, Jena, Germany 2Systems Biology/Bioinformatics Group, Leibniz Institute for Natural Product Research and Infection Biology Hans Knll Institute, Jena, Germany 3Department of Human Nutrition, Institute of Nutrition, University of Jena, Jena, Germany 4Department of Clinical Nutrition, German Institute of Human Nutrition, Potsdam-Rehbrcke, Nuthetal, Germany Stanford University, United States of America Conceived and designed the experiments: CK RG MR SS. Analyzed the data: CK LFdF SW. Wrote the paper: CK LFdF SS. Received 2011 Jan 14; Accepted 2011 May 24. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestric Continue reading >>

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  1. manohman

    Why can't fat be converted into Glucose?

    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?

  2. Czarcasm

    manohman said: ↑
    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?
    Click to expand... Both glucose and fatty acids can be stored in the body as either glycogen for glucose (stored mainly in the liver or skeletal cells) or for FA's, as triacylglycerides (stored in adipose cells). We cannot store excess protein. It's either used to make other proteins, or flushed out of the body if in excess; that's generally the case but we try to make use of some of that energy instead of throwing it all away.
    When a person is deprived of nutrition for a period of time and glycogen stores are depleted, the body will immediately seek out alternative energy sources. Fats (stored for use) are the first priority over protein (which requires the breakdown of tissues such as muscle). We can mobilize these FA's to the liver and convert them to Acetyl-CoA to be used in the TCA cycle and generate much needed energy. On the contrary, when a person eats in excess (a fatty meal high in protein), it's more efficient to store fatty acids as TAG's over glycogen simply because glycogen is extremely hydrophilic and attracts excess water weight; fatty acids are largely stored anhydrously and so you essentially get more bang for your buck. This is evolutionary significant and why birds are able to stay light weight but fly for periods at a time, or why bears are able to hibernate for months at a time. Proteins on the other hand may be used anabolically to build up active tissues (such as when your working out those muscles), unless you live a sedentary lifestyle (less anabolism and therefore, less use of the proteins). As part of the excretion process, protein must be broken down to urea to avoid toxic ammonia and in doing so, the Liver can extract some of that usable energy for storage as glycogen.
    Also, it is worth noting that it is indeed possible to convert FA's to glucose but the pathway can be a little complex and so in terms of energy storage, is not very efficient. The process involves converting Acetyl-CoA to Acetone (transported out of mitochondria to cytosol) where it's converted to Pyruvate which can then be used in the Gluconeogenesis pathway to make Glucose and eventually stored as Glycogen. Have a look for yourself if your interested: http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002116.g003/originalimage (and this excludes the whole glycogenesis pathway, which hasn't even begun yet).
    TLDR: it's because proteins have no ability to be stored in the body, but we can convert them to glycogen for storage during the breakdown process for excretion. Also, in terms of energy, it's a more efficient process than converting FA's to glycogen for storage.

  3. soccerman93

    This is where biochem comes in handy. Czarcasm gives a really good in depth answer, but a simpler approach is to count carbons. The first step of gluconeogenesis(formation of glucose) requires pyruvate, a 3 carbon molecule. Acetyl Co-A is a 2 carbon molecule, and most animals lack the enzymes (malate synthase and isocitrate lyase) required to convert acetyl co-A into a 3 carbon molecule suitable for the gluconeogenesis pathway. The ketogenic pathway is not efficient, as czarcasm pointed out. While acetyl co-A can indeed be used to form citric acid intermediates, these intermediates will be used in forming ATP, not glucose. Fatty acid oxidation does not yield suitable amounts of pyruvate, which is required for gluconeogenesis. This is part of why losing weight is fairly difficult for those that are overweight, we can't efficiently directly convert fat to glucose, which we need a fairly constant supply of. Sorry, that got a little long-winded

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Gluconeogenesis - An Overview | Sciencedirect Topics

Gluconeogenesis is the process that leads to the generation of glucose from a variety of sources such as pyruvate, lactate, glycerol, and certain amino acids. Larry R. Engelking, in Textbook of Veterinary Physiological Chemistry (Third Edition) , 2015 Gluconeogenesis occurs in the liver and kidneys. Gluconeogenesis supplies the needs for plasma glucose between meals. Gluconeogenesis is stimulated by the diabetogenic hormones (glucagon, growth hormone, epinephrine, and cortisol). Gluconeogenic substrates include glycerol, lactate, propionate, and certain amino acids. PEP carboxykinase catalyzes the rate-limiting reaction in gluconeogenesis. The dicarboxylic acid shuttle moves hydrocarbons from pyruvate to PEP in gluconeogenesis. Gluconeogenesis is a continual process in carnivores and ruminant animals, therefore they have little need to store glycogen in their liver cells. Of the amino acids transported to liver from muscle during exercise and starvation, Ala predominates. b-Aminoisobutyrate, generated from pyrimidine degradation, is a (minor) gluconeogenic substrate. N.V. Bhagavan, Chung-Eun Ha, in Essentials of Medical Biochemistry , 2011 Gluconeogenesis refers to synthesis of ne 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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Gluconeogenesis Flashcards | Quizlet

What is the definition of gluconeogensis? the synthesis of glucose from noncarbohydrate precursors how many days do the direct glucose reserves sufficient for the needs of the body? how many grams of glucose does the brain need daily? how many grams of glucose does the entire body need daily? how many grams of glucose are in body fluids to use for the body? how mans grams of readily mobilized glucose are there in glycogen stores? What is the major site of gluconeogenesis? mostly by the liver, and a smaller amount in the kidney 1. decreased insulin/glucagon ratio as in an overnight fast 3. high protein-low carb diet (need minimum of 50 g carb for insulin secretion) 4. stress; due to the hormones cortisol and epinephrine which are elevated under these conditions What are the 4 major non-carbohydrate presursors used as substrates for gluconeogenesis? 2. amino acids (muscle protein degradation in skeletal muscle) 3. glycerol (triglyceride breakdown in adipose tissue) what is lactate's role in the gluconeogenic pathway? 1. during vigorous exercise, lactate buildup and NADH 2. NADH can be reoxidized during the reduction of pyruvate to lactate 3. lactate is then returned to the liver, wh Continue reading >>

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Popular Questions

  1. manohman

    Why can't fat be converted into Glucose?

    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?

  2. Czarcasm

    manohman said: ↑
    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?
    Click to expand... Both glucose and fatty acids can be stored in the body as either glycogen for glucose (stored mainly in the liver or skeletal cells) or for FA's, as triacylglycerides (stored in adipose cells). We cannot store excess protein. It's either used to make other proteins, or flushed out of the body if in excess; that's generally the case but we try to make use of some of that energy instead of throwing it all away.
    When a person is deprived of nutrition for a period of time and glycogen stores are depleted, the body will immediately seek out alternative energy sources. Fats (stored for use) are the first priority over protein (which requires the breakdown of tissues such as muscle). We can mobilize these FA's to the liver and convert them to Acetyl-CoA to be used in the TCA cycle and generate much needed energy. On the contrary, when a person eats in excess (a fatty meal high in protein), it's more efficient to store fatty acids as TAG's over glycogen simply because glycogen is extremely hydrophilic and attracts excess water weight; fatty acids are largely stored anhydrously and so you essentially get more bang for your buck. This is evolutionary significant and why birds are able to stay light weight but fly for periods at a time, or why bears are able to hibernate for months at a time. Proteins on the other hand may be used anabolically to build up active tissues (such as when your working out those muscles), unless you live a sedentary lifestyle (less anabolism and therefore, less use of the proteins). As part of the excretion process, protein must be broken down to urea to avoid toxic ammonia and in doing so, the Liver can extract some of that usable energy for storage as glycogen.
    Also, it is worth noting that it is indeed possible to convert FA's to glucose but the pathway can be a little complex and so in terms of energy storage, is not very efficient. The process involves converting Acetyl-CoA to Acetone (transported out of mitochondria to cytosol) where it's converted to Pyruvate which can then be used in the Gluconeogenesis pathway to make Glucose and eventually stored as Glycogen. Have a look for yourself if your interested: http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002116.g003/originalimage (and this excludes the whole glycogenesis pathway, which hasn't even begun yet).
    TLDR: it's because proteins have no ability to be stored in the body, but we can convert them to glycogen for storage during the breakdown process for excretion. Also, in terms of energy, it's a more efficient process than converting FA's to glycogen for storage.

  3. soccerman93

    This is where biochem comes in handy. Czarcasm gives a really good in depth answer, but a simpler approach is to count carbons. The first step of gluconeogenesis(formation of glucose) requires pyruvate, a 3 carbon molecule. Acetyl Co-A is a 2 carbon molecule, and most animals lack the enzymes (malate synthase and isocitrate lyase) required to convert acetyl co-A into a 3 carbon molecule suitable for the gluconeogenesis pathway. The ketogenic pathway is not efficient, as czarcasm pointed out. While acetyl co-A can indeed be used to form citric acid intermediates, these intermediates will be used in forming ATP, not glucose. Fatty acid oxidation does not yield suitable amounts of pyruvate, which is required for gluconeogenesis. This is part of why losing weight is fairly difficult for those that are overweight, we can't efficiently directly convert fat to glucose, which we need a fairly constant supply of. Sorry, that got a little long-winded

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