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The Common Pathway For The Oxidation Of Glucose And Fatty Acid Is

Carbohydrate, Protein And Lipid Metabolism Notes

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 Energy and Metabolic Rate? Direct calorimetry A Bomb Calorimeter, or constant-volume calorimeter, is used to measure the energy released by food during complete oxidization. The food is placed in a sealed metal container surrounded by water in an insulated container. The food is ignited by an electrical spark and the temperature change of a known volume of water is used to calculate the energy released by the food. Standard caloric values for macronutrients are: Carbohydrates: 4.1 kcal/g Protein: 5.3 kcal/g (but in the body is only 4.1 kcal/g due to incomplete oxidation) Fat: 9.3 kcal/g Ethanol: Continue reading >>

The Citric Acid Cycle: The Central Pathway Of Carbohydrate, Lipid & Amino Acid Metabolism | Harper's Illustrated Biochemistry, 30e | Accessmedicine | Mcgraw-hill Medical

The Citric Acid Cycle: The Central Pathway Of Carbohydrate, Lipid & Amino Acid Metabolism | Harper's Illustrated Biochemistry, 30e | Accessmedicine | Mcgraw-hill Medical

The citric acid cycle (the Krebs or tricarboxylic acid cycle) is a sequence of reactions in mitochondria that oxidizes the acetyl moiety of acetyl-CoA to CO2 and reduces coenzymes that are reoxidized through the electron transport chain (see Chapter 13 ), linked to the formation of ATP. The citric acid cycle is the final common pathway for the oxidation of carbohydrate, lipid, and protein because glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA or intermediates of the cycle. It also has a central role in gluconeogenesis, lipogenesis, and interconversion of amino acids. Many of these processes occur in most tissues, but liver is the only tissue in which all occur to a significant extent. The repercussions are therefore profound when, for example, large numbers of hepatic cells are damaged as in acute hepatitis or replaced by connective tissue (as in cirrhosis). The few genetic defects of citric acid cycle enzymes that have been reported are associated with severe neurological damage as a result of very considerably impaired ATP formation in the central nervous system. Hyperammonemia, as occurs in advanced liver disease, leads to loss of consciousness, coma, and convulsions as a result of impaired activity of the citric acid cycle, leading to reduced formation of ATP. Ammonia both depletes citric acid cycle intermediates (by withdrawing -ketoglutarate for the formation of glutamate and glutamine) and also inhibits the oxidative decarboxylation of -ketoglutarate. THE CITRIC ACID CYCLE PROVIDES SUBSTRATES FOR THE RESPIRATORY CHAIN The cycle starts with reaction between the acetyl moiety of acetyl-CoA and the four-carbon dicarboxylic acid oxaloacetate, forming a six-carbon tricarboxylic acid, citrate. In the subsequent reactions, two molecules of CO2 Continue reading >>

A General Overview Of The Major Metabolic Pathways

A General Overview Of The Major Metabolic Pathways

A general overview of the major metabolic pathways Assistant Professor, Universidade FernandoPessoa Metabolism is the set of chemical rections that occur in a cell, which enable it to keep living, growing and dividing.Metabolic processes are usually classified as: catabolism - obtaining energy and reducing power from nutrients. anabolism - production of new cell components, usually through processes that require energy and reducing power obtained from nutrient catabolism. There is a very large number of metabolic pathways. In humans, the most important metabolic pathways are: glycolysis - glucose oxidation in order to obtain ATP citric acid cycle (Krebs' cycle) - acetyl-CoA oxidation in order to obtain GTP and valuable intermediates. oxidative phosphorylation - disposal of the electrons released by glycolysis and citric acid cycle. Much of the energy released in this process can be stored as ATP. pentose phosphate pathway - synthesis of pentoses and release of the reducing power needed for anabolic reactions. urea cycle - disposal of NH4+ in less toxic forms fatty acid -oxidation - fatty acids breakdown into acetyl-CoA, to be used by the Krebs' cycle. gluconeogenesis - glucose synthesis from smaller percursors, to be used by the brain. Click on the picture to get information on each pathway Metabolic pathways interact in a complex way in order to allow an adequate regulation. This interaction includes the enzymatic control of each pathway, each organ's metabolic profile and hormone control . Flow is regulated in the gluconeogenesis-specific reactions. Pyruvate carboxilase is activated by acetyl-CoA, which signals the abundance of citric acid cycle intermediates, i.e., a decreased need of glucose. The citric acid cycle is regulated mostly by substrate availability, prod Continue reading >>

The Common Pathway For The Oxidation Of Glucose And Free Fatty Acids Is....?

The Common Pathway For The Oxidation Of Glucose And Free Fatty Acids Is....?

The common pathway for the oxidation of glucose and free fatty acids is....? Update: This was a review question in my advanced nutrition class. The common pathway for the oxidation of glucose and free fatty acids is: Are you sure you want to delete this answer? 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, adult content, spam, insulting other members, show more I think this answer 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 comment violates the Community Guidelines Chat or rant, adult content, spam, insulting other members, show more I think this comment 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 Upload failed. Please upload a file larger than 100x100 pixels We are experiencing some problems, please try again. You can only upload files of type PNG, JPG, or JPEG. You can only upload files of type 3GP, 3GP Continue reading >>

The Citric Acid Cycle - Biochemistry - Ncbi Bookshelf

The Citric Acid Cycle - Biochemistry - Ncbi Bookshelf

Mitochondrion. The double membrane of the mitochondrion is evident in this electron micrograph. The numerous invaginations of the inner mitochondrial membrane are called cristae. The oxidative decarboxylation of pyruvate and the sequence of reactions (more...) 17.0.1. An Overview of the Citric Acid Cycle: The citric acid cycle is the central metabolic hub of the cell. It is the gateway to the aerobic metabolism of any molecule that can be transformed into an acetyl group or dicarboxylic acid. The cycle is also an important source of precursors, not only for the storage forms of fuels, but also for the building blocks of many other molecules such as amino acids, nucleotide bases, cholesterol, and porphyrin (the organic component of heme). What is the function of the citric acid cycle in transforming fuel molecules into ATP ? Recall that fuel molecules are carbon compounds that are capable of being oxidizedof losing electrons (Chapter 14). The citric acid cycle includes a series of oxidation-reduction reactions that result in the oxidation of an acetyl group to two molecules of carbon dioxide. The overall pattern of the citric acid cycle is shown in Figure 17.2 . A four- carbon compound (oxaloacetate) condenses with a two-carbon acetyl unit to yield a six-carbon tricarboxylic acid (citrate). An isomer of citrate is then oxidatively decarboxylated. The resulting five-carbon compound (-ketoglutarate) also is oxidatively decarboxylated to yield a four-carbon compound (succinate). Oxaloacetate is then regenerated from succinate. Two carbon atoms enter the cycle as an acetyl unit and two carbon atoms leave the cycle in the form of two molecules of carbon dioxide. Three hydride ions (hence, six electrons) are transferred to three molecules of nicotinamide adenine dinucleotide Continue reading >>

Glycolysis

Glycolysis

Glucose G6P F6P F1,6BP GADP DHAP 1,3BPG 3PG 2PG PEP Pyruvate HK PGI PFK ALDO TPI GAPDH PGK PGM ENO PK Glycolysis The metabolic pathway of glycolysis converts glucose to pyruvate by via a series of intermediate metabolites. Each chemical modification (red box) is performed by a different enzyme. Steps 1 and 3 consume ATP (blue) and steps 7 and 10 produce ATP (yellow). Since steps 6-10 occur twice per glucose molecule, this leads to a net production of ATP. Summary of aerobic respiration Glycolysis (from glycose, an older term[1] for glucose + -lysis degradation) is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy molecules ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).[2][3] Glycolysis is a determined sequence of ten enzyme-catalyzed reactions. The intermediates provide entry points to glycolysis. For example, most monosaccharides, such as fructose and galactose, can be converted to one of these intermediates. The intermediates may also be directly useful. For example, the intermediate dihydroxyacetone phosphate (DHAP) is a source of the glycerol that combines with fatty acids to form fat. Glycolysis is an oxygen independent metabolic pathway, meaning that it does not use molecular oxygen (i.e. atmospheric oxygen) for any of its reactions. However the products of glycolysis (pyruvate and NADH + H+) are sometimes metabolized using atmospheric oxygen.[4] When molecular oxygen is used for the metabolism of the products of glycolysis the process is usually referred to as aerobic, whereas if no oxygen is used the process is said to be anaerobic.[5] Thus, glycolysis occurs, with variations, in nearly all organisms, both aerobic and a Continue reading >>

Fatty Acid Oxidation And Synthesis

Fatty Acid Oxidation And Synthesis

Fatty acid -oxidation is a multi step process by which fatty acids are broken down by various tissues to produce energy. It involves first getting the fatty acid into the cytosol and then transferring it to the mitochondria where -oxidation takes place. -oxidation involves activation to acyl-CoA by conjugation with coenzyme A in the cytosol, conversion to acylcarnitine for transport across the mitochondrial membrane and conversion back to acyl-CoA inside the mitochondrion where fatty acid oxidation (-oxidation) takes place. -oxidation involves a repeated sequence of four enzyme activities that results in the release of an acetyl-CoA unit, a molecule of FADH2 and a molecule of NADH + H+. The acetyl-CoA then enters the mitochondrial tricarboxylic acid cycle (TCA) where it is oxidized to CO2 and H2O with the generation of additional FADH2 and NADH + H+. The NADH and FADH2 produced by both fatty acid -oxidation and the TCA cycle are used by the electron transport chain to generate ATP. Fatty acid synthesis (lipogenesis) is the process by which end products of glucose catabolism are converted to fatty acids, which are subsequently esterified with glycerol to form the triacylglycerols that are packaged in VLDL and secreted from the liver. Lipogenesis starts with acetyl-CoA and builds up by the addition of two carbons units donated by malonyl-CoA, generated by the ATP-dependant carboxylation of acetyl-CoA. The activated donor of two carbon units is malonyl-CoA, the elongation reaction being driven by the release of CO2. Fatty acid synthesis occurs in the cytoplasm in contrast to -oxidation which occurs in the mitochondria. In eukaryotes the enzymes for fatty acid synthesis are organized into a multienzyme complex called fatty acid synthetase. The intermediates in fatty acid s 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 >>

Section 16.1oxidation Of Glucose And Fatty Acids To Co2

Section 16.1oxidation Of Glucose And Fatty Acids To Co2

The complete aerobic oxidation of glucose is coupled to the synthesis of as many as 36 molecules of ATP: Glycolysis, the initial stage of glucose metabolism, takes place in the cytosol and does not involve molecular O. It produces a small amount of ATP and the three-carbon compound pyruvate. In aerobic cells, pyruvate formed in glycolysis is transported into the mitochondria, where it is oxidized by O to CO. Via chemiosmotic coupling, the oxidation of pyruvate in the mitochondria generates the bulk of the ATP produced during the conversion of glucose to CO. In this section, we discuss the biochemical pathways that oxidize glucose and fatty acids to CO and HO; the fate of the released electrons is described in the next section. Go to: Cytosolic Enzymes Convert Glucose to Pyruvate A set of 10 enzymes catalyze the reactions, constituting the glycolytic pathway, that degrade one molecule of glucose to two molecules of pyruvate (Figure 16-3). All the metabolic intermediates between glucose and pyruvate are watersoluble phosphorylated compounds. Four molecules of ATP are formed from ADP in glycolysis (reactions 6 and 9). However, two ATP molecules are consumed during earlier steps of this pathway: the first by the addition of a phosphate residue to glucose in the reaction catalyzed by hexokinase (reaction 1), and the second by the addition of a second phosphate to fructose 6-phosphate in the reaction catalyzed by phosphofructokinase-1 (reaction 3). Thus there is a net gain of two ATP molecules. The balanced chemical equation for the conversion of glucose to pyruvate shows that four hydrogen atoms (four protons and four electrons) are also formed: (For convenience, we show pyruvate in its un-ionized form, pyruvic acid, although at physiological pH it would be largely dissociat Continue reading >>

Energy - Metabiolab

Energy - Metabiolab

Energy metabolism is the general process by which all living cells acquire and use the energy needed to stay alive, to grow, and to reproduce. By coupling oxidation of nutrients with high-energy compounds synthesis, particularly ATP which works as the main chemical energy carrier in all cells, cells become able to capture the released energy while breaking the chemical bonds of nutrient molecules. The human body uses three types of molecules to yield the necessary energy to drive ATP synthesis: fats, proteins, and carbohydrates. Lipids are broken down into fatty acids, proteins into amino acids, and carbohydrates into glucose. There are two main mechanisms of ATP synthesis: oxidative phosphorylation/ATP synthesis , the process by which ATP is synthesized from ADP and inorganic phosphate (Pi) that takes place in mitochondrion substrate-level phosphorylation, in which ATP is synthesized through the transfer of high-energy phosphoryl groups from high-energy compounds to ADP. The latter occurs in both the mitochondrion, during the tricarboxylic acid (TCA) cycle , and in the cytoplasm, during glycolysis . Most cells use glucose for ATP synthesis, but there are other fuel molecules (fatty acids, proteins) that are equally important for maintaining human bodys equilibrium or homeostasis. However, some cells rely only on glucose for ATP synthesis as they are devoid of functional mitochondria (red blood cells, cancer cells,) and unable to oxidize neither fatty acids nor amino acids. But, even in cells that can use all nutrients, the type of food substrate that is oxidized changes according to the physiological situation of the cell, such as the fed and fasting states. Although fatty acids, amino acids, and glucose oxidation pathways begin differently, all these mechanisms ultim Continue reading >>

Metabolic Pathways

Metabolic Pathways

There are three groups of molecules that form the core building blocks and fuel substrates in the body: carbohydrates (glucose and other sugars); proteins and their constituent amino acids; and lipids and their constituent fatty acids. The biochemical processes that allow these molecules to be synthesized and stored (anabolism) or broken down to generate energy (catabolism) are referred to as metabolic pathways. Glucose metabolism involves the anabolic pathways of gluconeogenesis and glycogenesis, and the catabolic pathways of glycogenolysis and glycolysis. Lipid metabolism involves the anabolic pathways of fatty acid synthesis and lipogenesis and the catabolic pathways of lipolysis and fatty acid oxidation. Protein metabolism involves the anabolic pathways of amino acid synthesis and protein synthesis and the catabolic pathways of proteolysis and amino acid oxidation. Under conditions when glucose levels inside the cell are low (such as fasting, sustained exercise, starvation or diabetes), lipid and protein catabolism includes the synthesis (ketogenesis) and utilization (ketolysis) of ketone bodies. The end products of glycolysis, fatty acid oxidation, amino acid oxidation and ketone body degradation can be oxidised to carbon dioxide and water via the sequential actions of the tricarboxylic acid cycle and oxidative phosphorylation, generating many molecules of the high energy substrate adenosine triphosphate (ATP). Interplay between metabolic pathways The interplay between glucose metabolism, lipid metabolism, ketone body metabolism and protein and amino acid metabolism is summarized in Figure 1. Amino acids can be a source of glucose synthesis as well as energy production and excess glucose that is not required for energy production can be stored as glycogen or metabo Continue reading >>

Metabolic Pathway - Wikipedia

Metabolic Pathway - Wikipedia

In biochemistry , a metabolic pathway is a linked series of chemical reactions occurring within a cell . The reactants, products, and intermediates of an enzymatic reaction are known as metabolites , which are modified by a sequence of chemical reactions catalyzed by enzymes . [1] :26 In most cases a metabolic pathway, the product of one enzyme acts as the substrate for the next. However, set products are considered waste and removed from the cell. [2] These enzymes often require dietary minerals, vitamins, and other cofactors to function. Different metabolic pathways function based on the position within a eukaryotic cell and the significance of the pathway in the given compartment of the cell. [3] For instance, the citric acid cycle , electron transport chain , and oxidative phosphorylation all take place in the mitochondrial membrane. [4] :73, 74 & 109 In contrast, glycolysis , pentose phosphate pathway , and fatty acid biosynthesis all occur in the cytosol of a cell. [5] :441442 There are two types of metabolic pathways that are characterized by their ability to either synthesize molecules with the utilization of energy ( anabolic pathway ) or break down of complex molecules by releasing energy in the process ( catabolic pathway ). [6] The two pathways complement each other in that the energy released from one is used up by the other. The degradative process of a catabolic pathway provides the energy required to conduct a biosynthesis of an anabolic pathway. [6] In addition to the two distinct metabolic pathways is the amphibolic pathway, which can be either catabolic or anabolic based on the need for or the availability of energy. [7] Pathways are required for the maintenance of homeostasis within an organism and the flux of metabolites through a pathway is regula Continue reading >>

Beta Oxidation - An Overview | Sciencedirect Topics

Beta Oxidation - An Overview | Sciencedirect Topics

Fatty acid oxidation is the dominant energy source for the heart when circulating FFAs are high, as after an overnight fast or after catecholamine simulation.10 Fatty acid oxidation is called -oxidation because the bond between the (C2) and carbon (C3) of the fatty acid is broken during each round of the cycle, which involves four enzymatic steps as illustrated in Fig. 2 and reviewed elsewhere.6,7 First, a double bond is introduced between C2 and C3 by the action of the acyl-CoA dehydrogenases (ACADs). ACADs are flavoenzymes that have a noncovalently bound FAD moiety on each subunit to accept electrons during the dehydrogenation reaction. The next step is hydration of the newly introduced double bond. This reaction is stereospecific, forming only the L isomer, and is catalyzed by enoyl-CoA hydratases (EHs). The product of the reaction, l-3-hydroxyacyl-CoA, is oxidized in step three by hydroxyacyl-CoA dehydrogenases (HADs) using NAD+ as an electron acceptor and yielding 3-ketoacyl-CoA. Finally, -ketothiolases complete the cycle using free CoA to generate a new acyl-CoA molecule which is two carbons shorter, and an acetyl-CoA. The shortened acyl-CoA can repeat this cycle until completely reduced to acetyl-CoA units. Fatty acids are thus a rich source of energy. A single C18 fatty acid is broken into 9 acetyl-CoA which by way of the TCA cycle and electron transport chain produces 90 ATP. The same number of carbons from glucose (three glucose molecules) would also produce 90 ATP. The advantage to fatty acid oxidation are the electrons captured at steps one and three of the -oxidation cycle, which yield an additional 30 ATP for a single C18 fatty acid, bringing the total to 120 ATP per 18 carbons versus 90 ATP for the same number of glucose carbons. Ernesto R. Bongarzone, . Continue reading >>

Fatty Acid Oxidation And Its Relation With Insulin Resistance And Associated Disorders

Fatty Acid Oxidation And Its Relation With Insulin Resistance And Associated Disorders

Fatty Acid Oxidation and Its Relation with Insulin Resistance and Associated Disorders Faculty of Medicine and Dentistry, 423 HMRB University of Alberta, Edmonton, Alberta T6G 2S2 (Canada) Alterations in muscle fatty acid metabolism have been implicated in mediating the severity of insulin resistance. In the insulin resistant heart fatty acids are favored as an energy source over glucose, which is thus associated with increased fatty acid oxidation, and an overall decrease in glycolysis and glucose oxidation. In addition, excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. In animal studies, mice fed a high fat diet (HFD) show cardiac insulin resistance in which the accumulation of intra-myocardial diacylglycerol has been implicated, likely involving parallel signaling pathways. A HFD also results in accumulation of fatty acid oxidation byproducts in muscle, further contributing to insulin resistance. Carnitine acetyltransferase (CrAT) has an essential role in the cardiomyocyte because of its need for large amounts of carnitine. In the cardiomyocyte, carnitine switches energy substrate preference in the heart from fatty acid oxidation to glucose oxidation. This carnitine-induced switch in fatty acid oxidation to glucose oxidation is due to the presence of cytosolic CrAT and reverse CrAT activity. Accordingly, inhibition of fatty acid oxidation, or stimulation of CrAT, may be a novel approach to treatment of insulin resistance. Alterations in muscle fatty acid metabolism have been implicated in mediating the severity of insulin resistance. As muscle fatty acid uptake and oxidation is increased in insulin-resistant and diabetic individuals, increased fatty acid metabolism can thus directly impair glucose metabolism Continue reading >>

The Study Of Metabolic Pathways

The Study Of Metabolic Pathways

There are two main reasons for studying a metabolic pathway: (1) to describe, in quantitative terms, the chemical changes catalyzed by the component enzymes of the route; and (2) to describe the various intracellular controls that govern the rate at which the pathway functions. Studies with whole organisms or organs can provide information that one substance is converted to another and that this process is localized in a certain tissue; for example, experiments can show that urea, the chief nitrogen-containing end product of protein metabolism in mammals, is formed exclusively in the liver. They cannot reveal, however, the details of the enzymatic steps involved. Clues to the identity of the products involved, and to the possible chemical changes effected by component enzymes, can be provided in any of four ways involving studies with either whole organisms or tissues. First, under stress or the imbalances associated with diseases, certain metabolites may accumulate to a greater extent than normal. Thus, during the stress of intense exercise, lactic acid appears in the blood, while glycogen, the form in which carbohydrate is stored in muscle, disappears. Such observations do not, however, prove that lactic acid is a normal intermediate of glycogen catabolism; rather, they show only that compounds capable of yielding lactic acid are likely to be normal intermediates. Indeed, in the example, lactic acid is formed in response to abnormal circumstances and is not directly formed in the pathways of carbohydrate catabolism. Second, the administration of metabolic poisons may lead to the accumulation of specific metabolites. If fluoroacetic acid or fluorocitric acid is ingested by animals, for example, citric acid accumulates in the liver. This correctly suggests that fluoroci Continue reading >>

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