Not to be confused with Glycogenesis or Glyceroneogenesis. Simplified Gluconeogenesis Pathway Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. From breakdown of proteins, these substrates include glucogenic amino acids (although not ketogenic amino acids); from breakdown of lipids (such as triglycerides), they include glycerol (although not fatty acids); and from other steps in metabolism they include pyruvate and lactate. Gluconeogenesis is one of several main mechanisms used by humans and many other animals to maintain blood glucose levels, avoiding low levels (hypoglycemia). Other means include the degradation of glycogen (glycogenolysis) and fatty acid catabolism. Gluconeogenesis is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In vertebrates, gluconeogenesis takes place mainly in the liver and, to a lesser extent, in the cortex of the kidneys. In ruminants, this tends to be a continuous process. In many other animals, the process occurs during periods of fasting, starvation, low-carbohydrate diets, or intense exercise. The process is highly endergonic until it is coupled to the hydrolysis of ATP or GTP, effectively making the process exergonic. For example, the pathway leading from pyruvate to glucose-6-phosphate requires 4 molecules of ATP and 2 molecules of GTP to proceed spontaneously. Gluconeogenesis is often associated with ketosis. Gluconeogenesis is also a target of therapy for type 2 diabetes, such as the antidiabetic drug, metformin, which inhibits glucose formation and stimulates glucose uptake by cells. In ruminants, because dietary carbohydrates tend to be metabolized by rumen organisms, gluconeogenesis occurs Continue reading >>
We Really Can Make Glucose From Fatty Acids After All!
Biochemistry textbooks generally tell us that we can't turn fatty acids into glucose. For example, on page 634 of the 2006 and 2008 editions of Biochemistry by Berg, Tymoczko, and Stryer, we find the following: Animals Cannot Convert Fatty Acids to Glucose It is important to note that animals are unable to effect the net synthesis of glucose from fatty acids. Specficially, acetyl CoA cannot be converted into pyruvate or oxaloacetate in animals. In fact this is so important that it should be written in italics and have its own bold heading! But it's not quite right. Making glucose from fatty acids is low-paying work. It's not the type of alchemy that would allow us to build imperial palaces out of sugar cubes or offer hourly sweet sacrifices upon the altar of the glorious god of glucose (God forbid!). But it can be done, and it'll help pay the bills when times are tight. I don't think any is converted for anyone not in ketosis. I read through the steps and it requires inputs only present in ketosis - i.e., the textbooks were correct for something like 99% of the population. In their day, they were probably correct for just about everyone except people starving from lack of food or people on hunger strikes and a few remaining Inuit still on their traditional diet. And, as Dr. Chris says, it's "low-paying work". An intellectual curiosity for sure, but in the metabolic scheme of things, probably largely irrelevant. I wouldn't be looking to curb any spikes by reducing fats! Those come for carbs first and proteins second. Any fats which REPLACE either of those will mean a lot less net glucose, not more. Basically, the statement that "animals can't convert fat to glucose" is no more incorrect than the often heard "glucose is the source of cellular energy", actually, much LESS Continue reading >>
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Fanatic Cook: The Human Body Cannot Make Glucose
Only plants can make glucose from scratch.* Humans must eat the plants, or eat animals that ate the plants, to obtain glucose. And humans absolutely need glucose to survive. This simple sugar is the sole source of energy for our red blood cells and the preferred source for other cells. We are utterly dependant on plants for our existence. (Not to mention that they release oxygen in the process of manufacturing glucose - oxygen that we also need to survive.) * And some algae like seaweed, and some bacteria. Glucose is a molecule with 6 carbon atoms bound together. Humans cannot harness the immense amount of energy needed to get 6 carbon atoms to bind together. Plants, however, can. It's quite a feat actually. They harness the energy from the sun to do this. Plants take in carbon dioxide, string together 6 carbons to make glucose for their fuel (starch is just a chain of glucoses), and give off the excess oxygen. Humans take in the oxygen given off from plants and use it to extract the energy from those bonds within the glucose molecule. (One pathway to extract that energy is called glycolysis. I'll return to glycolysis later.) The waste product, if you will, from our energy-extraction process is carbon dioxide. We exhale it. This is the same carbon dioxide that the plant takes in to make glucose - it needs those carbons. Humans and plants have a cyclical relationship. At night, plants respire just like us. They use oxygen to extract energy from the glucose they made during the day, giving off carbon dioxide in the process. There is a process our bodies evolved to supply glucose in a pinch. It's called gluconeogenesis ... the new making of glucose. Since we can't make glucose from scratch, this process allows us to reassemble preformed 3-carbon and 4-carbon molecules to Continue reading >>
We Really Can Make Glucose From Fatty Acids After All! O Textbook, How Thy Biochemistry Hast Deceived Me!
Biochemistry textbooks generally tell us that we can’t turn fatty acids into glucose. For example, on page 634 of the 2006 and 2008 editions of Biochemistry by Berg, Tymoczko, and Stryer, we find the following: Animals Cannot Convert Fatty Acids to Glucose It is important to note that animals are unable to effect the net synthesis of glucose from fatty acids. Specficially, acetyl CoA cannot be converted into pyruvate or oxaloacetate in animals. In fact this is so important that it should be written in italics and have its own bold heading! But it’s not quite right. Making glucose from fatty acids is low-paying work. It’s not the type of alchemy that would allow us to build imperial palaces out of sugar cubes or offer hourly sweet sacrifices upon the altar of the glorious god of glucose (God forbid!). But it can be done, and it’ll help pay the bills when times are tight. All Aboard the Acetyl CoA! When we’re running primarily on fatty acids, our livers break the bulk of these fatty acids down into two-carbon units called acetate. When acetate hangs out all by its lonesome like it does in a bottle of vinegar, it’s called acetic acid and it gives vinegar its characteristic smell. Our livers aren’t bottles of vinegar, however, and they do things a bit differently. They have a little shuttle called coenzyme A, or “CoA” for short, that carries acetate wherever it needs to go. When the acetate passenger is loaded onto the CoA shuttle, we refer to the whole shebang as acetyl CoA. As acetyl CoA moves its caboose along the biochemical railway, it eventually reaches a crossroads where it has to decide whether to enter the Land of Ketogenesis or traverse the TCA cycle. The Land of Ketogenesis is a quite magical place to which we’ll return in a few moments, but n Continue reading >>
- International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #82: Insulin Actions In Vivo: Glucose Metabolism Part 9 of 9
- World's first diabetes app will be able to check glucose levels without drawing a drop of blood and will be able to reveal what a can of coke REALLY does to sugar levels
- International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #59: Mechanisms of insulin signal transduction Part 3 of 8
Why We Can't Produce Glucose From Fat ? | Yahoo Answers
Are you sure you want to delete this answer? Best Answer: Fats are metabolized to acetyl-CoA. This molecule then enters the citric acid cycle when it is combined with oxaloacetate to make citrate. Further reactions degrade it to CO2 and produce NADH, FADH2, and GTP. For a molecule entering the cycle to produce sugar requires the net production of oxaloacetate. But for each acetyl-CoA that enters the cycle, two molecules of CO2 are produced, hence it just drives the cycle and doesn't produce anything but CO2. To produce oxaloacetate from acetyl-CoA (thereby using fat to make sugar, because oxaloacetate can undergo what is essentially reverse glycolysis and is dubbed gluconeogenesis) requires the glyoxylate shunt, which is a pathway that does not occur in humans. Wikipedia's article isn't bad: If you look at calories as units of potential energy, then fat has double plus the energy of glucose at 9 calories per gram of fat versus 4 for carbohydrates. Anyone who said glucose is WRONG. Glucose is a Sugar derivative fat is generaly either Ester, Glycerol or fatty Acids. or a mixture of them all. glucose is made from your body converting suger. We can. Fats can be burned to acetyl-CoA. If we have an excess of acetyl-CoA and low glucose, we produce glucose by gluconeogenesis. I think this question violates the Community Guidelines Chat or rant, adult content, spam, insulting other members, show more I think this question violates the Terms of Service Harm to minors, violence or threats, harassment or privacy invasion, impersonation or misrepresentation, fraud or phishing, show more If you believe your intellectual property has been infringed and would like to file a complaint, please see our Copyright/IP Policy I think this answer violates the Community Guidelines Chat or rant Continue reading >>
Can Sugars Be Produced From Fatty Acids? A Test Case For Pathway Analysis Tools
Can sugars be produced from fatty acids? A test case for pathway analysis tools Department of Bioinformatics, 2Bio Systems Analysis Group, Friedrich-Schiller-Universitt Jena, Ernst-Abbe-Platz 2, 07743 Jena, Germany and 3School of Life Sciences, Oxford Brookes University, Headington, Oxford, OX3 0BP, UK *To whom correspondence should be addressed. Search for other works by this author on: Department of Bioinformatics, 2Bio Systems Analysis Group, Friedrich-Schiller-Universitt Jena, Ernst-Abbe-Platz 2, 07743 Jena, Germany and 3School of Life Sciences, Oxford Brookes University, Headington, Oxford, OX3 0BP, UK *To whom correspondence should be addressed. Search for other works by this author on: Department of Bioinformatics, 2Bio Systems Analysis Group, Friedrich-Schiller-Universitt Jena, Ernst-Abbe-Platz 2, 07743 Jena, Germany and 3School of Life Sciences, Oxford Brookes University, Headington, Oxford, OX3 0BP, UK Search for other works by this author on: Department of Bioinformatics, 2Bio Systems Analysis Group, Friedrich-Schiller-Universitt Jena, Ernst-Abbe-Platz 2, 07743 Jena, Germany and 3School of Life Sciences, Oxford Brookes University, Headington, Oxford, OX3 0BP, UK Search for other works by this author on: Bioinformatics, Volume 25, Issue 1, 1 January 2009, Pages 152158, Luis F. de Figueiredo, Stefan Schuster, Christoph Kaleta, David A. Fell; Can sugars be produced from fatty acids? A test case for pathway analysis tools, Bioinformatics, Volume 25, Issue 1, 1 January 2009, Pages 152158, Motivation: In recent years, several methods have been proposed for determining metabolic pathways in an automated way based on network topology. The aim of this work is to analyse these methods by tackling a concrete example relevant in biochemistry. It concerns the question wh Continue reading >>
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 unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. This article has been cited by other articles in PMC. The question whether fatty acids can be converted into glucose in humans has a long standing tradition in biochemistry, and the expected answer is No. Using recent advances in Systems Biology in the form of large-scale metabolic reconstructions, we reassessed this question by performing a global investigation of a genome-scale human metabolic network, which had been reconstructed on the basis of experimental results. By elem Continue reading >>
Why Can Fatty Acids Not Be Converted Into Glucose? : Mcat
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What Is Gluconeogenesis? How Does Does It Control Blood Sugars?
What is gluconeogenesis? How does does it control blood sugars? by breaknutrition | Sep 12, 2017 | Ketogenic Diets | 8 comments Step into the low-carb world and soon enough youll hear the term GlucoNeoGenesis. GNG for short, is your bodys ability to construct glucose, a kind of sugar, out of molecules that arent glucose. It does this to ensure that, if you dont eat any carbs, the cells in your body that need glucose will still get enough of it. Its one reason why humans are so good at fasting or delaying death from starvation for weeks or months. We can meet our own need for glucose by producing it ourselves. What do I mean by cells in your body that need glucose? I mean a reliance on glucose to accomplish its basic physiological tasks over a long time maybe a lifetime. You then might ask, but is there a difference when meeting your glucose needs with GNG versus by eating carbs? Fair question. You could also ask although no one seems to is it better to meet your glucose needs through GNG than by eating carbs? Also a fair question I think but one people will most likely scoff at. These questions deserve more space than Im according them here, so theyll have to be wrestled with in a follow-up post. Background: why do we make our own glucose? As mentioned in the introduction, it helps us handle a lack of calories or carbohydrates but that can only be because at least some of our cells depend on glucose (or other monosaccharides ) to some significant degree. Most cells in your body do just fine using varying amounts of fatty acids, glucose, amino acids, lactate, ketones etc However, a few cell types well call obligate glucose users cant use any other fuel but glucose. Then there are what well call quasi obligate glucose users whose metabolisms are adapted to specialized fu Continue reading >>
Glucose Can Be Synthesized From Noncarbohydrate Precursors - Biochemistry - Ncbi Bookshelf
Glucose is formed by hydrolysis of glucose 6-phosphate in a reaction catalyzed by glucose 6-phosphatase. We will examine each of these steps in turn. 16.3.2. The Conversion of Pyruvate into Phosphoenolpyruvate Begins with the Formation of Oxaloacetate The first step in gluconeogenesis is the carboxylation of pyruvate to form oxaloacetate at the expense of a molecule of ATP . Then, oxaloacetate is decarboxylated and phosphorylated to yield phosphoenolpyruvate, at the expense of the high phosphoryl-transfer potential of GTP . Both of these reactions take place inside the mitochondria. The first reaction is catalyzed by pyruvate carboxylase and the second by phosphoenolpyruvate carboxykinase. The sum of these reactions is: Pyruvate carboxylase is of special interest because of its structural, catalytic, and allosteric properties. The N-terminal 300 to 350 amino acids form an ATP -grasp domain ( Figure 16.25 ), which is a widely used ATP-activating domain to be discussed in more detail when we investigate nucleotide biosynthesis ( Section 25.1.1 ). The C -terminal 80 amino acids constitute a biotin-binding domain ( Figure 16.26 ) that we will see again in fatty acid synthesis ( Section 22.4.1 ). Biotin is a covalently attached prosthetic group, which serves as a carrier of activated CO2. The carboxylate group of biotin is linked to the -amino group of a specific lysine residue by an amide bond ( Figure 16.27 ). Note that biotin is attached to pyruvate carboxylase by a long, flexible chain. The carboxylation of pyruvate takes place in three stages: Recall that, in aqueous solutions, CO2 exists as HCO3- with the aid of carbonic anhydrase (Section 9.2). The HCO3- is activated to carboxyphosphate. This activated CO2 is subsequently bonded to the N-1 atom of the biotin ring to Continue reading >>
Evolving Health: Why Can't We Convert Fat To Glucose?
As evident by many sugar-laden soda pop "potbellies" of North America, lipogenesis can obviously occur from drinking and eating too much sugar (1). Wouldnt it be just grand to reverse the process and be able to lose all that fat via gluconeogenesis? Unfortunately mammals do not have the ability to synthesize glucose from fats (1). The fact is that once glucose is converted to acetyl coA there is no method of getting back to glucose. The pyruvate dehydrogenase reaction that converts pyruvate to acetyl CoA is not reversible (1p252). Because lipid metabolism produces acetyl CoA via beta-oxidation, there can be no conversion to pyruvate or oxaloacetate that may have been used for gluconeogenesis (1p252). Further, the two carbons in the acetyl CoA molecule are lost upon entering the citric acid cycle (1p252). Thus, the acetyl CoA is used for energy (1p252). There are some fatty acids that have an odd number of carbon atoms that can be converted to glucose, but these are not common in the diet (1p253). Maybe they should be made more common. Do they taste good? 1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009. Continue reading >>
Chapter 19 : Carbohydrate Biosynthesis
Thus the synthesis of glucose from pyruvate is a relativelycostly process. Much of this high energy cost is necessary toensure that gluconeogenesis is irreversible. Under intracellularconditions, the overall free-energy change of glycolysis is atleast -63 kJ/mol. Under the same conditions the overallfree-energy change of gluconeogenesis from pyruvate is alsohighly negative. Thus glycolysis and gluconeogenesis are bothessentially irreversible processes under intracellularconditions. Citric Acid Cycle Intermediates and Many Amino Acids AreGlucogenic The biosynthetic pathway to glucose described above allows thenet synthesis of glucose not only from pyruvate but also from thecitric acid cycle intermediates citrate, isocitrate,-ketoglutarate, succinate, fumarate, and malate. All may undergooxidation in the citric acid cycle to yield oxaloacetate.However, only three carbon atoms of oxaloacetate are convertedinto glucose; the fourth is released as CO in the conversion ofoxaloacetate to phosphoenolpyruvate by PEP carboxykinase (Fig.19-3). In Chapter 17 we showed that some or all of thecarbon atoms of many of the amino acids derived from proteins areultimately converted by mammals into either pyruvate or certainintermediates of the citric acid cycle. Such amino acids cantherefore undergo net conversion into glucose and are calledglucogenic amino acids (Table 19-3). Alanine and glutamine makeespecially important contributions in that they are the principalmolecules used to transport amino groups from extrahepatictissues to the liver. After removal of their amino groups inliver mitochondria, the carbon skeletons remaining (pyruvate anda-ketoglutarate, respectively) are readily funneled intogluconeogenesis. In contrast, there is no net conversion of even-carbon fattyacids into gl Continue reading >>
Nutrition. Chap 7: Energy Metabolism.
Sort Proteins: makes nonessential AA that are in short supply. Removes excess AA & converts them to other AA, or deaminates them & converts them to glucose or fatty acids. Removes ammonia from blood & converts it to urea for excretion. Makes DNA/RNA. & many proteins. >> Other: Detoxifies alcohol, drugs, poison, & excretes them. Helps dismantle old RBC's & captures the iron for recycling. Stores most vitamins, & many minerals. Activates Vitamin D. AA: Before entering metabolic pathways, AA are deaminated (lose their nitrogen amino group). deamination produces ammonia (which provides nitrogen to make nonessential AA. Remaining ammonia is excreted by urea in liver/kid. AA pathway: can enter pathways as pyruvate/Acetyl CoA/others enter krebs as compounds other than Acetyl CoA. AA that make glucose either by pyruvate or krebs cycle are glucogenic. AA that are degraded to Acetyl CoA are Ketogenic. Thus, proteins unlike fats, are a good source of glucose when carbs aren't available. In the liver: because of capillary network the liver is first to get alcohol saturated blood. liver cells are the only other cells in the body that can make sufficient quantities of dehydrogenase, to oxidize alcohol at a decent rate. >> Alcohol affects every organ of the body, bu t the most dramatic evidence is disruptive behavior is in the liver. Normally the liver prefers fatty acids for fuel, & it packages excess out. But when alcohol is there it has to process it first. >> Continue reading >>
Why Can't Fat Produce Glucose?
Tousief Irshad Ahmed Sirwal Author has 77 answers and 106.2k answer views Acetyl CoA is NOT a substrate for gluconeogenesis in animals 1. Pyruvate dehydrogenase reaction is irreversible. So, acetyl CoA cannot be converted back to pyruvate. 2. 2C Acetyl CoA enters the TCA cycle by condensing with 4C oxaloacetate. 2 molecules of CO2 are released & the oxaloacetate is regenerated. There is no NET production of oxaloacetate. Animals cannot convert fat into glucose with minimal exceptions 1. Propionyl CoA derived from odd chain fatty acids are converted to Succinyl CoA Glucogenic 2. Glycerol derived from triglycerides are glucogenic. Answered Mar 26, 2017 Author has 942 answers and 259.1k answer views Yijia Xiong pointed out that the glycerol portion of triglycerides (fats) can indeed be converted to glucose. It is not so energy-inefficient that it is avoided by our bodies. If nutritionally, we are in a gluconeogenesis mode (building up glucose stores rather than consuming them), glycerol would be a perfectly acceptable precursor. However, I think the original question had more to do with the vast bulk of the triglycerides that are not glycerol, but are fatty acids. And it is true that we cant produce glucose from fatty acids. The reason is that the catabolic reactions of fatty acids break off two carbon atoms at a time as Acetyl-CoA. But our metabolic suite of pathways has no way to convert a two-carbon fragment to glucose. The end product of glycolysis is pyruvate, a three-carbon compound. Pyruvate can be back-synthesized into glucose. But the committing reaction for the Krebs cycle is the pyruvate dehydrogenase step, forming acetyl-CoA. That reaction is not reversible. Once pyruvate loses a carbon atom, it cant go back. The three main macronutrients are carbohydrates, pr Continue reading >>
Does Fat Convert To Glucose In The Body?
Your body is an amazing machine that is able to extract energy from just about anything you eat. While glucose is your body's preferred energy source, you can't convert fat into glucose for energy; instead, fatty acids or ketones are used to supply your body with energy from fat. Video of the Day Fat is a concentrated source of energy, and it generally supplies about half the energy you burn daily. During digestion and metabolism, the fat in the food you eat is broken down into fatty acids and glycerol, which are emulsified and absorbed into your blood stream. While some tissues -- including your muscles -- can use fatty acids for energy, your brain can't convert fatty acids to fuel. If you eat more fat than your body needs, the extra is stored in fat cells for later use. Fat has more than twice as many calories per gram as carbs and protein, which makes it an efficient form of stored energy. It would take more than 20 pounds of glycogen -- a type of carbohydrate used for fuel -- to store the same amount of energy in just 10 pounds of fat. Your Body Makes Glucose From Carbs Almost all the glucose in your body originated from carbohydrates, which come from the fruit, vegetables, grains and milk in your diet. When you eat these carb-containing foods, your digestive system breaks them down into glucose, which is then used for energy by your cells. Any excess glucose is converted into glycogen, then stored in your muscles and liver for later use. Once you can't store any more glucose or glycogen, your body stores any leftover carbs as fat. Glucose is your brain's preferred source of energy. However, when glucose is in short supply, your brain can use ketones -- which are derived from fat -- for fuel. Since your brain accounts for approximately one-fifth of your daily calori Continue reading >>