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Glucose Can Be Used To Make Fatty Acids True Or False

True Or False

True Or False

(See related pages) 1 Anabolic reactions are those chemical reactions that release energy, usually by the breakdown of larger organic molecules into smaller organic molecules. 2 Aerobic cellular respiration and ventilation describe two very different processes. 3 Within a cell, the oxygen used during aerobic metabolism of nutrients ultimately becomes water. 4 Damage to the mitochondria of a cell would inhibit glycolysis. 7 To summarize glycolysis, one glucose molecule is broken down sequentially to two molecules of pyruvic acid, releasing two NADH + H+ molecules, and generating a net gain of two ATP. 8 It is common for certain tissues like skeletal muscle to derive energy (ATP) from anaerobic respiration on a daily basis without permanent injury or damage to the tissue. 9 Red blood cells only use glycolysis in the catabolism of glucose. 10 Phosphorylation of glucose "traps" the glucose molecule within the cell. 11 In aerobic respiration, pyruvic acid is formed from glucose but lactic acid is not. 12 The enzyme, glycogen phosphorylase, catalyzes the conversion of glycogen to glucose-1-phosphate. 13 Organic molecules with phosphate groups such as glucose 6-phosphate are cell "prisoners" because they cannot cross cell membranes. 14 The liver can supply the skeletal muscle with energy in the form of free glucose but the opposite is not true. 15 Tissue cells that are anaerobic would have to burn relatively more glucose molecules to maintain a steady supply of ATP than would those tissues that are supplied with oxygen. 16 During exercise, the liver can metabolize the lactic acid produced by the skeletal muscle cells and provide glucose to the cells of the body. 17 During aerobic respiration, the reaction that results in the conversion of pyruvic acid to acetyl CoA and CO2, oc Continue reading >>

Fatty Acid Metabolism

Fatty Acid Metabolism

Fatty acid metabolism consists of catabolic processes that generate energy, and anabolic processes that create biologically important molecules (triglycerides, phospholipids, second messengers, local hormones and ketone bodies).[1] Fatty acids are a family of molecules classified within the lipid macronutrient class. One role of fatty acids in animal metabolism is energy production, captured in the form of adenosine triphosphate (ATP). When compared to other macronutrient classes (carbohydrates and protein), fatty acids yield the most ATP on an energy per gram basis, when they are completely oxidized to CO2 and water by beta oxidation and the citric acid cycle.[2] Fatty acids (mainly in the form of triglycerides) are therefore the foremost storage form of fuel in most animals, and to a lesser extent in plants. In addition, fatty acids are important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus). Fatty acids can also be cleaved, or partially cleaved, from their chemical attachments in the cell membrane to form second messengers within the cell, and local hormones in the immediate vicinity of the cell. The prostaglandins made from arachidonic acid stored in the cell membrane, are probably the most well known group of these local hormones. Fatty acid catabolism[edit] A diagrammatic illustration of the process of lipolysis (in a fat cell) induced by high epinephrine and low insulin levels in the blood. Epinephrine binds to a beta-adrenergic receptor in the cell membrane of the adipocyte, which causes cAMP to be generated inside Continue reading >>

Biochemistry

Biochemistry

Sort what is the regulation of the citric acid cycle The citric acid cycle is regulated mostly by substrate availability, product inhibition and by some cycle intermediates. • pyruvate dehydrogenase: is inhibited by its products, acetyl-CoA and NADH • citrate synthase: is inhibited by its product, citrate. It is also inhibited by NADH and succinyl-CoA (which signal the abundance of citric acid cycle intermediates). • isocitrate dehydrogenase and a-ketoglutarate dehydrogenase: like citrate synthase, these are inhibited by NADH and succinyl-CoA. Isocitrate dehydrogenase is also inhibited by ATP and stimulated by ADP. All aforementioned dehydrogenases are stimulated by Ca2+. This makes sense in the muscle, since Ca2+ release from the sarcoplasmic reticulum triggers muscle contraction, which requires a lot of energy. This way, the same "second messenger" activates an energy-demanding task and the means to produce that energy. What is the regulation of fatty acid metabolism Acyl-CoA movement into the mitochondrion is a crucial factor in regulation. Malonyl-CoA (which is present in the cytoplasm in high amounts when metabolic fuels are abundant) inhibits carnitine acyltransferase, thereby preventing acyl-CoA from entering the mitochondrion. Furthermore, 3-hydroxyacyl-CoA dehydrogenase is inhibited by NADH and thiolase is inhibited by acetyl-CoA, so that fatty acids wil not be oxidized when there are plenty of energy-yielding substrates in the cell. Explain in overview the metabolic reactions in the body that lead to the formation of ketone bodies (Ketogenesis). Ketogenesis is the process by which ketone bodies are produced as a result of fatty acid breakdown. Ketone bodies are produced mainly in the mitochondria of liver cells, and synthesis can occur in response to una Continue reading >>

Triglycerides - What Do They Do?

Triglycerides - What Do They Do?

Triglycerides are a type of fat that plays a major role as an energy source when they are metabolized in the human body. They are very rich in energy, containing double the energy of either carbohydrates or proteins that can also be used to supply energy to the body. As a normal component of the vascular system, triglycerides are continually in circulation ready to be metabolized to provide a source of energy. When present in excess, triglycerides can be stored in fatty deposits, which may lead to obesity and related health conditions if it extends over time. Triglyceride Metabolism The chemical structure of triglycerides is composed of a glycerol molecule that is bound to three fatty acid chains. These three fatty acids can vary on each triglyceride to create many different types of triglycerides. Through a process known as lipolysis, triglycerides are broken down to release the fatty acids from the monoacylglycerol in the intestine, simultaneously secreting lipases and bile. The triglycerides can then be reconstructed in the enterocytes to incorporate cholesterol and proteins to form chylomicrons. Chylomicrons then move into the lymph system and the vascular system to be transported around the body as an energy supply. It is the glycerol component of the triglyceride that is the most useful to the body in providing a source of energy, as it is easily converted into glucose, which can be used to supply the brain with energy. The fatty acids can also provide energy, but must be converted to a ketone chemical structure in order to be utilized. Triglycerides as a complete molecule cannot be absorbed into the cells of the body from the bloodstream and must be broken down into its separate components in order to be utilized. Triglyceride Storage When there is an excess of t Continue reading >>

Connections Between Cellular Respiration And Other Pathways

Connections Between Cellular Respiration And Other Pathways

So far, we’ve spent a lot of time describing the pathways used to break down glucose. When you sit down for lunch, you might have a turkey sandwich, a veggie burger, or a salad, but you’re probably not going to dig in to a bowl of pure glucose. How, then, are the other components of food – such as proteins, lipids, and non-glucose carbohydrates – broken down to generate ATP? As it turns out, the cellular respiration pathways we’ve already seen are central to the extraction of energy from all these different molecules. Amino acids, lipids, and other carbohydrates can be converted to various intermediates of glycolysis and the citric acid cycle, allowing them to slip into the cellular respiration pathway through a multitude of side doors. Once these molecules enter the pathway, it makes no difference where they came from: they’ll simply go through the remaining steps, yielding NADH, FADH​, and ATP. Simplified image of cellular respiration pathways, showing the different stages at which various types of molecules can enter. Glycolysis: Sugars, glycerol from fats, and some types of amino acids can enter cellular respiration during glycolysis. Pyruvate oxidation: Some types of amino acids can enter as pyruvate. Citric acid cycle: Fatty acids from fats and certain types of amino acids can enter as acetyl CoA, and other types of amino acids can enter as citric acid cycle intermediates. In addition, not every molecule that enters cellular respiration will complete the entire pathway. Just as various types of molecules can feed into cellular respiration through different intermediates, so intermediates of glycolysis and the citric acid cycle may be removed at various stages and used to make other molecules. For instance, many intermediates of glycolysis and the cit Continue reading >>

Ch 25 Flashcards | Quizlet

Ch 25 Flashcards | Quizlet

a. is the conversion of one molecule of glucose into two molecules of pyruvic acid. b. is the conversion of two molecules of glucose into one molecule of pyruvic acid. c. concludes with formation of acetyl coenzyme A. d. generates a usable total of 4 ATP molecules. e. requires oxygen for efficient conversion of glucose into pyruvic acid. a. is the conversion of one molecule of glucose into two molecules of pyruvic acid. a. is formed through oxidation of pyruvic acid. b. formation requires pyruvate dehydrogenase. ATP is produced through chemiosmosis in the cytosol of the cell, and may occur under aerobic or anaerobic conditions. Which of the following places the events of glucose catabolism in the correct order? a. glycolysis, formation of acetyl coA, Krebs cycle, electron transport chain reactions b. glycolysis, Krebs cycle, formation of acetyl coA, electron transport chain reactions c. glycolysis, anaerobic respiration, Krebs cycle, electron transport chain reactions d. glycolysis, Krebs cycle, anaerobic respiration, electron transport chain reactions e. formation of acetyl coA, glycolysis, electron transport chain reactions a. glycolysis, formation of acetyl coA, Krebs cycle, electron transport chain reactions Glycolysis requires only phosphorylation and does not involve dephosphorylation. If adequate O2 is present in the mitochondria, pyruvic acid will be converted to ______; if conditions are anaerobic, pyruvic acid will be converted to ______. The first molecule formed in the Krebs cycle is Which of the following statements about the process of deamination is FALSE? b. required for oxidation of amino acids in the Krebs cycle d. all of these choices are possible fates of an amino acid. e. none of these choices is possible fates of an amino acid. d. all of these cho Continue reading >>

We Really Can Make Glucose From Fatty Acids After All! O Textbook, How Thy Biochemistry Hast Deceived Me!

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 >>

Metabolism Of Fatty Acids That Results In The

Metabolism Of Fatty Acids That Results In The

98) The amine group removed from an amino acid must be converted to ________ before being eliminated from the human body.99) Insulin levels in the blood are elevated in response to which of the following?100) Which of the following is not an action of insulin on liver cells?3.2 True/False Questions1) Chemical reactions are only able to occur in one direction.Answer: FALSEDiff: 3 Page Ref: 572) Phosphorylation reactions are specific examples of a condensation reaction.Answer: FALSEDiff: 4 Page Ref: 583) Sucrose is synthesized from the condensation of fructose and glucose.Answer: TRUEDiff: 4 Page Ref: 584) The following reaction is an example of an oxidation: FAD + 2 H+ FADH2Answer: FALSEDiff: 5 Page Ref: 5921 5) According to the first law of thermodynamics, energy cannot be created or destroyed.Answer: TRUEDiff: 4 Page Ref: 596) Potential energy describes the energy possessed by an object in motion.Answer: FALSEDiff: 4 Page Ref: 607) A reaction is at equilibrium when the rate of the forward and reverse reactions are equal.Answer: TRUEDiff: 4 Page Ref: 618) Energy-releasing reactions occur spontaneously.Answer: TRUEDiff: 4 Page Ref: 619) Energy-requiring reactions will always proceed spontaneously in the forward direction.Answer: FALSEDiff: 4 Page Ref: 6110) An increase in the concentration of a product will increase the rate of a reaction in the reversedirection.Answer: TRUEDiff: 4 Page Ref: 6111) An increase in temperature increases the potential energy of molecules. This preview has intentionally blurred sections. Sign up to view the full version. Continue reading >>

There Are Four Major Categories Of Organic Compounds Found In Living Cells.

There Are Four Major Categories Of Organic Compounds Found In Living Cells.

Macromolecules Up to this point we have considered only small molecules. Many of the molecules important to biological processes are HUGE. These are known as macromolecules. Most macromolecules are polymers, which are long chains of subunits called monomers. These subunits are often very similar to each other, and for all the diversity of polymers (and living things in general) there are only about 40 - 50 common monomers. Making and breaking polymers Joining two monomers is achieved by a process known as dehydration synthesis. One monomer gives up a hydroxyl (OH) group and one gives up a (H). These combine to make a water molecule. Hence the name dehydration synthesis. Polymers are broken apart by a process known as hydrolysis. Bonds between monomers are broken by the addition of water. (3.3, pg 36) Carbohydrates Carbohydrates are the sugars and their polymers. Simple sugars are called monosaccharides. These can be joined to form polysaccharides (3.5, pg 38). Glucose is an important monosaccharide. Sucrose, a disaccharide (consisting of two monosaccharides), is table sugar. (Note the ending "ose" common to most sugars.) Polysaccharides may be made from thousands of simple sugars linked together. These large molecules may be used for storage of energy or for structure. First a couple of storage examples: Starch is a storage polysaccharide of plants. Its is a giant string of glucoses. The plant can utilize the energy in starch by first hydrolyzing it, making the glucose available. Most animals can also hydrolyze starch. That's why we eat it. Animals store glycogen as a supply of glucose. It is stored in the liver and muscles. (3.7, pg 39) And some examples of structural carbohydrates: Cellulose is a polysaccharide produced by plants. Its is a component of the cell walls. Continue reading >>

Harvesting Energy

Harvesting Energy

Why do we humans eat food? What do we need it for, and get out of it? W O R K T O G E T H E R Cellular respiration is an: Endergonic process Exergonic process Exergonic OR endergonic process, depending on the organism. In which organelle does cellular respiration occur? Chloroplast Mitochondria Depends on whether it’s a plant or an animal. What is “food†(i.e. source of metabolic energy) for plants? Sunlight Sugar Water Oxygen Minerals cristae mitochondrion inner membrane outer membrane intermembrane space matrix Cellular respiration takes place in the mitochondria. net exergonic “downhill†reaction glucose protein amino acids CO2 + H2O + heat ADP + heat Review: ATP is produced and used in coupled reactions endergonic (ATP synthesis) exergonic (ATP breakdown) exergonic (glucose breakdown) endergonic (protein synthesis) Energy released by the exergonic breakdown of glucose is used for: The endergonic production of ATP. The exergonic production of ATP. The endergonic breakdown of ATP. The exergonic breakdown of ATP. 2 pyruvate electron transport chain (cytosol) (mitochondrion) glycolysis Krebs (citric acid) cycle 2 acetyl CoA 2 NADH Total 36 or 38 ATPs 2 ATP 6 NADH 2 FADH2 glucose 32 or 34 ATPs 2 ATP 2 NADH Overview Glycolysis splits sugar into two 3-carbon chains (pyruvate), producing 2 ATPs Cellular respiration breaks the sugar down further, producing 32-34 ATPs. NADH and FADH (derived from vitamins B3 and B2) act as electron carriers. 34 or 36 ATP in mitochondria– oxygen required in cytosol– no oxygen required glycolysis glucose fermentation pyruvate 2 ATP cellular respiration O2 if no O2 available ethanol + CO2 or lactic acid CO2 H2O fructose bisphosphate ATP ADP 1 Glucose activation in cytosol 2 Energy harvest NAD+ NADH ATP AD Continue reading >>

Metabolism

Metabolism

Sort Catabolism Degradation from large complex molecules to smaller simple ones: 1) Carbohydrate Catabolism: a) Glycolysis b) Penthose Phosphate Passway c) Kerbs Cycle (Cytric Acid Cycle) d) Electron transport Chain e) Glycogenolysis 2) Lipid Catabolism a) β oxidation b) Ketone metabolism c) Cholestrol catabolism 3) Protein Catabolism 4) Nucleic Acid Catabolism Glycolysis: Definition and Enzymes Converts Glucose to Pyruvate (or Lactate in anaerobic conditions) Net energy yield: 2 ATP, 2 NADH Steps: 1) Glucose ---> Glucose-6p 2) Glucose-6p <---> Fructose-6p 3) Fructose-6p ---> Fruktose-1,6 bisphosphate --- 4) Fruktose-1,6 bisphosphate <--->Glyceraldehyde-3p + DHAP 4-a) Glyceraldehyde-3p <---> DHAP 5) Glyceraldehyde-3p <---> 1,3-Biphosphoglycerate 6) 1,3-Biphosphoglycerate <---> 3-Phosphoglycerate 7) 3-Phosphoglycerate <---> 2-Phosphoglycerate 8) 2-Phosphoglycerate ----> Phosphoenylpyruvate (PEP) 9) PEP ---> Pyruvate Enzymes: 1) Hexokonase (Glucokinase in liver), 2) Glucose 6-p isomerase (Phosphoglucose isomerase) 3) PFK, 4) Aldolase, 4-a) Triose-phosphate isomerase, 5) Glyceraldehyde-phosphate dehydrogenase, 6) Phosphoglycerate kinase, 7) Phosphoglycerate mutase, 8) Enolase, 9) Pyruvate Kinase Hexokinase, PFK and Pyruvate Kinase are irreversible and regulatory PFK is Rate Limiting Step ATP is used in steps 1 & 3 NADH produced in 5 ATP produced in 6 & 9 Glycolysis: regulators 1) Hexokinase inhibited by:G6P (In Liver: Glucokinase regulated by: Glucokinase regulatory protein: GKRP) 2) PFK-1 Stimulated by AMP & Fructose-2,6-bisphosphate⁰ and inhibited by ATP & Citrate PFK-2 stimulated by Insukine and inhibited by Glucagon 3) Pyruvate kinase activated by: fructose-1,6-bisphosphate and Insuline⁰, Inhibited by ATP, Acetyl-CoA, Glucagon⁰ and Alanine⁰ ⁰Liver specific G 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

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 >>

The Body’s Fuel Sources

The Body’s Fuel Sources

The Body’s Fuel Sources Our ability to run, bicycle, ski, swim, and row hinges on the capacity of the body to extract energy from ingested food. As potential fuel sources, the carbohydrate, fat, and protein in the foods that you eat follow different metabolic paths in the body, but they all ultimately yield water, carbon dioxide, and a chemical energy called adenosine triphosphate (ATP). Think of ATP molecules as high-energy compounds or batteries that store energy. Anytime you need energy—to breathe, to tie your shoes, or to cycle 100 miles (160 km)—your body uses ATP molecules. ATP, in fact, is the only molecule able to provide energy to muscle fibers to power muscle contractions. Creatine phosphate (CP), like ATP, is also stored in small amounts within cells. It’s another high-energy compound that can be rapidly mobilized to help fuel short, explosive efforts. To sustain physical activity, however, cells must constantly replenish both CP and ATP. Our daily food choices resupply the potential energy, or fuel, that the body requires to continue to function normally. This energy takes three forms: carbohydrate, fat, and protein. (See table 2.1, Estimated Energy Stores in Humans.) The body can store some of these fuels in a form that offers muscles an immediate source of energy. Carbohydrates, such as sugar and starch, for example, are readily broken down into glucose, the body’s principal energy source. Glucose can be used immediately as fuel, or can be sent to the liver and muscles and stored as glycogen. During exercise, muscle glycogen is converted back into glucose, which only the muscle fibers can use as fuel. The liver converts its glycogen back into glucose, too; however, it’s released directly into the bloodstream to maintain your blood sugar (blood Continue reading >>

Gluconeogenesis - An Overview | Sciencedirect Topics

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 new glucose from noncarbohydrate precursors, provides glucose when dietary intake is insufficient or absent. It also is essential in the regulation of acid-base balance, amino acid metabolism, and synthesis of carbohydrate derived structural components. Gluconeogenesis occurs in liver and kidneys. The precursors of gluconeogenesis are lactate, glycerol, amino acids, and with propionate making a minor contribution. The gluconeogenesis pathway consumes ATP, which is derived primarily from the oxidation of fatty acids. The pathway uses several enzymes of the glycolysis with the exception of enzymes Continue reading >>

Dynamic Adaptation Of Nutrient Utilization In Humans

Dynamic Adaptation Of Nutrient Utilization In Humans

Most cells use glucose for ATP synthesis, but there are other fuel molecules equally important for maintaining the body's equilibrium or homeostasis. Indeed, although the oxidation pathways of fatty acids, amino acids, and glucose begin differently, these mechanisms ultimately converge onto a common pathway, the TCA cycle, occurring within the mitochondria (Figure 1). As mentioned earlier, the ATP yield obtained from lipid oxidation is over twice the amount obtained from carbohydrates and amino acids. So why don't all cells simply use lipids as fuel? In fact, many different cells do oxidize fatty acids for ATP production (Figure 2). Between meals, cardiac muscle cells meet 90% of their ATP demands by oxidizing fatty acids. Although these proportions may fall to about 60% depending on the nutritional status and the intensity of contractions, fatty acids may be considered the major fuel consumed by cardiac muscle. Skeletal muscle cells also oxidize lipids. Indeed, fatty acids are the main source of energy in skeletal muscle during rest and mild-intensity exercise. As exercise intensity increases, glucose oxidation surpasses fatty acid oxidation. Other secondary factors that influence the substrate of choice for muscle include exercise duration, gender, and training status. Another tissue that utilizes fatty acids in high amount is adipose tissue. Since adipose tissue is the storehouse of body fat, one might conclude that, during fasting, the source of fatty acids for adipose tissue cells is their own stock. Skeletal muscle and adipose tissue cells also utilize glucose in significant proportions, but only at the absorptive stage - that is, right after a regular meal. Other organs that use primarily fatty acid oxidation are the kidney and the liver. The cortex cells of the Continue reading >>

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