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Can Fatty Acids Be Converted To Glucose?

Metabolic Pathways - Metabolism, Insulin And Other Hormones - Diapedia, The Living Textbook Of Diabetes

Metabolic Pathways - Metabolism, Insulin And Other Hormones - Diapedia, The Living Textbook Of Diabetes

You are viewing a previous revision of this article. Click here to view the current version. 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). 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 Continue reading >>

Why Can Fatty Acids Not Be Converted Into Glucose? : Mcat

Why Can Fatty Acids Not Be Converted Into Glucose? : Mcat

Rudeness or trolling will not be tolerated. Be nice to each other, hating on other users won't help you get extra points on the MCAT, so why do it? Do not post any question information from any resource in the title of your post. These are considered spoilers and should be marked as such. For an example format for submitting pictures of questions from practice material click here Do not link to content that infringes on copyright laws (MCAT torrents, third party resources, etc). Do not post repeat "GOOD LUCK", "TEST SCORE", or test reaction posts. We have one "stickied" post for each exam and score release day, contain all test day discussion/reactions to that thread only. Do not discuss any specific information from your actual MCAT exam. You have signed an examinee agreement, and it will be enforced on this subreddit. Do not intentionally advertise paid products or services of any sort. These posts will be removed and the user banned without warning, subject to the discretion of the mod team Learn More All of the above rules are subject to moderator discretion C/P = Chemical and Physical Foundations of Biological Systems CARS = Critical Analysis and Reasoning Skills B/B = Biological and Biochemical Foundations of Living Systems P/S = Psychological, Social, and Biological Foundations of Behavior Continue reading >>

Intermediary Metabolism

Intermediary Metabolism

may in certain cells or at certain times be used as a source of ATP . The complexity of the mechanism by which cells use glucose may make you fervently hope that a similarly-constructed system is not needed for each kind of fuel. And indeed it is not. One of the great advantages of the step-by-step oxidation of glucose into CO2 and H2O is that several of the intermediate compounds formed in the process link glucose metabolism to the metabolism of other food molecules. For example, when fats are used as fuel, the glycerol portion of the molecule is converted into PGAL and enters the glycolytic pathway at that point. Fatty acids are converted into molecules of acetyl-CoA and enter the respiratory pathway to be oxidized in the mitochondria. The amino acids liberated by the hydrolysis of proteins can also serve as fuel. First, the nitrogen is removed, a process called deamination . The remaining fragments then enter the respiratory pathway at several points. the amino acids Gly , Ser , Ala , and Cys are converted into pyruvic acid and enter the mitochondria to be respired. acetyl-CoA and several intermediates in the citric acid cycle serve as entry points for other amino acid fragments (shown in blue). These links thus permit the respiration of excess fats and proteins in the diet. No special mechanism of cellular respiration is needed by those animals that depend largely on ingested fats (e.g., many birds) or proteins (e.g., carnivores) for their energy supply. Much of the protein we consume is ultimately converted into glucose (a process called gluconeogenesis ) to provide fuel for the brain and other tissues. Although all our foods are interconvertible to some extent, they are not completely so. In other words, no single food can supply all our anabolic needs. We can in Continue reading >>

Multiple Choice Quiz 1

Multiple Choice Quiz 1

(See related pages) 1 Which one of the following would not be a nutrient? 2 Most vitamins, minerals, and water all have this in common: 3 When the body metabolizes nutrients for energy, fats yield about _______ times the energy as carbohydrates or proteins. 4 A calorie is the amount of energy necessary to raise the temperature of one gram of _________ one degree __________. 5 One piece of apple pie would yield about 6 The disaccharide that most people think of as table sugar is 7 When lactose is digested, it yields two monosaccharides called 8 The complex carbohydrate (polysaccharide) that is digested to the monosaccharide, glucose, and is found in vegetables, fruits, and grains and is called 9 If excess glucose is present in the body, the glucose first will be stored as __________ in muscle and the liver. 10 Triglycerides that contain one or more double covalent bonds between carbon atoms of their fatty acids are called 11 Bubbling hydrogen gas through polyunsaturated vegetable oil will cause the oil to become more 12 The lipid that is a component of the plasma membrane and can be used to form bile salts and steroid hormones is 13 The American Heart Association recommends that saturated fats should contribute no more than 10% of total fat intake. Excess fats, especially cholesterol and saturated fat, can increase the risk of 16 The daily-recommended consumption amount of protein for a healthy adult is about _____% of total kilocalorie intake per day. 20 Inorganic nutrients that are necessary for normal metabolism are called 23 When a molecule loses an electron, that molecule is said to be ___________ and often a(n) _____________ ion is lost along with the electron. 25 When a hydrogen ion and an associated electron are lost from a nutrient molecule, which of the followi Continue reading >>

Gluconeogenesis And Beta-oxiation

Gluconeogenesis And Beta-oxiation

Glucogneogenesis Essentially a reversal of glycolysis Pyruvate ïƒ Glucose Requires three irreversible steps of glycolysis to be bypassed Glucose ‘trapping’ The first step in glycolysis Phosphofructokinase The rate limiting step in glycolysis Pyruvate kinase The final step in glycolysis Gluconeogenesis can only occur in the liver Mainly cytoplasmic Glucose 6-phosphatase Reversal of glucose trapping Catalysed by hexokinase/glucokinase Required for release of glucose into the bloodstream Begins with transport of G6P into vesicles of endoplasmic reticulum Special transporter required Hydrolysis of G6P By glucose 6-phosphatase (G6Pase) Glucose goes back into cytoplasm through GLUT-9 Glucose released into blood via GLUT-2 Remember these are very active and [glucose]blood = [glucose]liver G6Pase is increased in activity on starvation Regulated by increased transcription/translation of gene Fructose 1,6 bisphosphatase Reversal of F6P ïƒ F16BP Above reaction stimulated by allosteric effector F26BP F26BP made by PFK-2 F26BP inhibits F16BPase and stimulates PFK So when F26BP is high, glycolysis is favoured Phosphorylation of PFK-2 converts it into F26BPase Thus the amount of F26BP decreases PFK is inhibited and F16BPase increases So when F26BP is low, gluconeogensis is favoured Phosphoryation is catalysed by cAMP-dependant protein kinase Protein kinase A PKA will be active when cAMP is high When glucagon has bound to its receptors on the liver cell membrane F16BPase is activated when glucagon levels are high As in starvation! Gluconeogenesis & Glycolysis When starving glucagon ï‚ ïƒ ï‚ [cAMP] [F2,6BP]  No stimulus for PFK ïƒ no glycolysis No inhibition for F1,6BPase ïƒ favours gluconeogenesis Reverse PEPïƒ pyruvate Glycolytic ste Continue reading >>

Alcohol Metabolism

Alcohol Metabolism

The metabolic pathways for the disposal of excess NADH and the consequent blocking of other normal metabolic pathways is shown in the graphic on the left. The conversion of pyruvic acid to lactic acid requires NADH: Pyruvic Acid + NADH + H+ ---> Lactic Acid + NAD+ This pyruvic acid normally made by transamination of amino acids, is intended for conversion into glucose by gluconeogenesis. This pathway is inhibited by low concentrations of pyruvic acid, since it has been converted to lactic acid. The final result may be acidosis from lactic acid build-up and hypoglycemia from lack of glucose synthesis. Excess NADH may be used as a reducing agent in two pathways--one to synthesize glycerol (from a glycolysis intermediate) and the other to synthesis fatty acids. As a result, heavy drinkers may initially be overweight. The NADH may be used directly in the electron transport chain to synthesize ATP as a source of energy. This reaction has the direct effect of inhibiting the normal oxidation of fats in the fatty acid spiral and citric acid cycle. Fats may accumulate or acetyl CoA may accumulate with the resulting production of ketone bodies. Accumulation of fat in the liver can be alleviated by secreting lipids into the blood stream. The higher lipid levels in the blood may be responsible for heart attacks. A central role in the toxicity of alcohol may be played by acetaldehyde itself. Although the liver converts acetaldehyde into acetic acid, it reaches a saturation point where some of it escapes into the blood stream. The accumulated acetaldehyde exerts its toxic effects by inhibiting the mitochondria reactions and functions. The alcoholic is a victim of a vicious circle; a high acetaldehyde level impairs mitochondria function, metabolism of acetaldehyde to acetic acid decr Continue reading >>

Macronutrients

Macronutrients

Overview Carbohydrates, fats and proteins are macronutrients. We require them in relatively large amounts for normal function and good health. These are also energy-yielding nutrients, meaning these nutrients provide calories. On This Page: What are Carbohydrates? Carbohydrates Understanding Carbohydrates Every few years, carbohydrates are vilified as public enemy number one and are accused of being the root of obesity, diabetes, heart disease and more. Carb-bashers shun yogurt and fruit and fill up on bun-less cheeseburgers. Instead of beans, they eat bacon. They dine on the tops of pizza and toss the crusts into the trash. They so vehemently avoid carbs and spout off a list of their evils that they may have you fearing your food. Rest assured, you can and should eat carbohydrates. In fact, much of the world relies on carbohydrates as their major source of energy. Rice, for instance, is a staple in Southeast Asia. The carbohydrate-rich potato was so important to the people of Ireland that when the blight devastated the potato crop in the mid 1800s, much of the population was wiped out. What are Carbohydrates? The basic structure of carbohydrates is a sugar molecule, and they are classified by how many sugar molecules they contain. Simple carbohydrates, usually referred to as sugars, are naturally present in fruit, milk and other unprocessed foods. Plant carbohydrates can be refined into table sugar and syrups, which are then added to foods such as sodas, desserts, sweetened yogurts and more. Simple carbohydrates may be single sugar molecules called monosaccharides or two monosaccharides joined together called disaccharides. Glucose, a monosaccharide, is the most abundant sugar molecule and is the preferred energy source for the brain. It is a part of all disaccharides Continue reading >>

Fatty Acids In Energy Metabolism Of The Central Nervous System

Fatty Acids In Energy Metabolism Of The Central Nervous System

BioMed Research International Volume 2014 (2014), Article ID 472459, 22 pages 1Institute of Molecular Biology and Biophysics, Siberian Division of the Russian Academy of Medical Sciences (SB RAMS), 2 Timakova st., Novosibirsk 630117, Russia 2Department of Surgery, Drexel University College of Medicine, Philadelphia, PA, USA Academic Editor: Ancha Baranova Copyright © 2014 Alexander Panov et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract In this review, we analyze the current hypotheses regarding energy metabolism in the neurons and astroglia. Recently, it was shown that up to 20% of the total brain’s energy is provided by mitochondrial oxidation of fatty acids. However, the existing hypotheses consider glucose, or its derivative lactate, as the only main energy substrate for the brain. Astroglia metabolically supports the neurons by providing lactate as a substrate for neuronal mitochondria. In addition, a significant amount of neuromediators, glutamate and GABA, is transported into neurons and also serves as substrates for mitochondria. Thus, neuronal mitochondria may simultaneously oxidize several substrates. Astrocytes have to replenish the pool of neuromediators by synthesis de novo, which requires large amounts of energy. In this review, we made an attempt to reconcile -oxidation of fatty acids by astrocytic mitochondria with the existing hypothesis on regulation of aerobic glycolysis. We suggest that, under condition of neuronal excitation, both metabolic pathways may exist simultaneously. We provide experimental evidence that isolated neuronal mitochondria may oxidize palmitoyl c Continue reading >>

Insulin And Glucagon

Insulin And Glucagon

Acrobat PDF file can be downloaded here. The islets of Langerhans The pancreatic Islets of Langerhans are the sites of production of insulin, glucagon and somatostatin. The figure below shows an immunofluorescence image in which antibodies specific for these hormones have been coupled to differing fluorescence markers. We can therefore identify those cells that produce each of these three peptide hormones. You can see that most of the tissue, around 80 %, is comprised of the insulin-secreting red-colored beta cells (ß-cells). The green cells are the α-cells (alpha cells) which produce glucagon. We see also some blue cells; these are the somatostatin secreting γ-cells (gamma cells). Note that all of these differing cells are in close proximity with one another. While they primarily produce hormones to be circulated in blood (endocrine effects), they also have marked paracrine effects. That is, the secretion products of each cell type exert actions on adjacent cells within the Islet. An Introduction to secretion of insulin and glucagon The nutrient-regulated control of the release of these hormones manages tissue metabolism and the blood levels of glucose, fatty acids, triglycerides and amino acids. They are responsible for homeostasis; the minute-to-minute regulation of the body's integrated metabolism and, thereby, stabilize our inner milieu. The mechanisms involved are extremely complex. Modern medical treatment of diabetes (rapidly becoming "public enemy number one") is based on insight into these mechanisms, some of which are not completely understood. I will attempt to give an introduction to this complicated biological picture in the following section. Somewhat deeper insight will come later. The Basics: secretion Let us begin with two extremely simplified figur Continue reading >>

Metabolism | Definition, Process, & Biology - Anaplerotic Routes | Britannica.com

Metabolism | Definition, Process, & Biology - Anaplerotic Routes | Britannica.com

See trusted Britannica articles at the top of every search. Download our free Chrome Extension Although the catabolism of carbohydrates can occur via a variety of routes, all give rise to pyruvate. During the catabolism of pyruvate, one carbon atom is lost as carbon dioxide and the remaining two form acetyl coenzyme A (reaction [37]); these two are involved in the TCA cycle ([41] and [42]). Because the TCA cycle is initiated by the condensation of acetyl coenzyme A with oxaloacetate, which is regenerated in each turn of the cycle, the removal of any intermediate from the cycle would cause the cycle to stop. Yet, various essential cell components are derived from -oxoglutarate, succinyl coenzyme A, and oxaloacetate, so that these compounds are, in fact, removed from the cycle. Microbial growth with a carbohydrate as the sole carbon source is thus possible only if a cellular process occurs that effects the net formation of some TCA cycle intermediate from an intermediate of carbohydrate catabolism. Such a process, which replenishes the TCA cycle, has been described as an anaplerotic reaction . The anaplerotic function may be carried out by either of two enzymes that catalyze the fixation of carbon dioxide onto a three-carbon compound , either pyruvate (reaction [50]) or phosphoenolpyruvate (PEP; [50a]) to form oxaloacetate, which has four carbon atoms. Both reactions require energy . In [50] it is supplied by the cleavage of ATP to ADP and inorganic phosphate (Pi), and in [50a] it is supplied by the release of the high-energy phosphate of PEP as inorganic phosphate. Pyruvate serves as a carbon dioxide acceptor not only in many bacteria and fungi but also in the livers and kidneys of higher organisms, including humans; PEP serves as the carbon dioxide acceptor in many bac Continue reading >>

Milk Composition - Milk Fat

Milk Composition - Milk Fat

Summary of Fatty Acid Synthesis Reactions: Each cycle through the malonyl-CoA pathway results in two carbons being added to the FA chain. The total reaction is (given here for synthesis of palmitate; C16): Acetyl-CoA + 7 Malonyl-CoA + 14 NADPH2 are catalyzed by Fatty Acid Synthetase to yield = The Fatty Acid Synthesis Pathway involves the following steps : The steps involved in the malonyl-CoA pathway occur with the growing FA chain esterified to an acyl carrier protein. Fatty acid synthetase is a large complex of enzymatic activities which are responsible for the reactions of FA synthesis. In addition, there are enzyme activities called acylthioesterases which are responsible for cleaving off the growing FA chain from the acyl carrier protein once it has reached a certain chain length. The long chain acylthioesterase is part of the fatty acid synthetase complex and cleaves off FA chain lengths longer that C16. The medium chain acylthioesterase cleaves off the growing FA chain at or before it reaches C16. In nonruminants, the medium chain acylthioesterase is cytoplasmic and cleaves off free FAs (unesterified). In the ruminant, the medium chain acylthioesterase is associated with the fatty acid synthetase complex and releases acyl-CoA thioesters. Below is a diagram of the pathway of fatty acid synthesis. Note that acetate carbons come into play twice, once as the source of acetyl-CoA to enter the malonyl-CoA pathway and once as the source of malonyl-CoA that adds the two carbons to each cycle of the fatty acid synthetase. In the latter case, conversion of acetyl-CoA to malonyl-CoA is the rate limiting step in fatty acid synthesis. The reaction is catalyzed by acetyl-CoA carboxylase, a biotinylated protein. Acetyl-CoA carboxylase activity is regulated by lactogenic hormo Continue reading >>

How Does Fat Get Converted To Calories?

How Does Fat Get Converted To Calories?

Opinions expressed by Forbes Contributors are their own. Answer by Bart Loews , passionate exercise enthusiast, on Quora : How is fat being converted into calories at cellular level? First lets get some term clarification: A calorie is a measure of energy, specifically heat. Its a measurement of an indirect use of your biological fuels. Your body doesnt really convert things to calories, it converts them to ATP which is used as energy. Calories are, sadly, the best way we have to measure this process.Ill assume that the point of this question is: How does fat turn into energy? Fat is a term used interchangeably with lipids and with adipose tissue. Lipids are molecules that consist of a hydrophobic tail with a hydrophilic head. Because of this polarized set up, they are able to cluster together to form barriers between water and non water, like bubbles. Your cell membranes are composed of lipids. Adipose tissue is what makes you fat. Adipose tissue stores lipids in the form of triglycerides or 3 fatty acid chains with a glycerol backbone. These triglycerides are what is broken down to be used for energy. Adipose tissue is made up of collections of adipocytes or fat cells. Adipose tissue is used for insulation, cushioning, and energy storage. You get a particular number of fat cells (between 30 and 300 billion) during adolescence and childhood. You don't lose them naturally, but you can gain more if they grow more than 4 fold from their original size. They grow and shrink as they take on more energy. Fat cells have a few other roles in the endocrine system, they release the hormone, Leptin when they receive energy from insulin. Leptin signals to your body that you're full. The more fat cells you have, the more leptin is released. It's been found that obese people are lep Continue reading >>

How Does The Body Adapt To Starvation?

How Does The Body Adapt To Starvation?

- [Instructor] In this video, I want to explore the question of how does our body adapt to periods of prolonged starvation. So in order to answer this question, I actually think it's helpful to remind ourselves first of a golden rule of homeostasis inside of our body. So in order to survive, remember that our body must be able to maintain proper blood glucose levels. I'm gonna go ahead and write we must be able to maintain glucose levels in our blood, and this is important even in periods of prolonged starvation, because it turns out that we need to maintain glucose levels above a certain concentration in order to survive, even if that concentration is lower than normal. And this of course brings up the question, well, how does our body maintain blood glucose levels? So let's go ahead and answer this question by starting off small. Let's say we have a mini case of starvation, let's say three or four hours after a meal. Your blood glucose levels begin to drop, and so what does your body do to resolve that? Well, at this point, it has a quick and easy solution. It turns to its glycogen stores in the liver. Remember that our body stores up these strings of glucose inside of our body so that we can easily pump it back into the blood when we're not eating. But unfortunately humans only have enough glycogen stores to last us about a day, so after a day of starvation, our body's pretty much reliant exclusively on the metabolic pathways involved in gluconeogenesis, which if you remember is the pathway by which we produce new or neo glucose. And we produce this glucose from non-carbohydrate precursor molecules. So let's think about what else we have in our body. Remember that our other two major storage fuels are fats, and we usually think about fatty acids containing most of th Continue reading >>

Basic Biochemistry | Digital Textbook Library

Basic Biochemistry | Digital Textbook Library

Vertebrates cannot convert fatty acids, or the acetate derived from them, to carbohydrates. Conversion of phosphoenolpyruvate to pyruvate and of pyruvate to acetyl-CoA is so exergonic as to be essentially irreversible. If a cell cannot convert acetate into phosphoenolpyruvate, acetate cannot serve as the starting material for the gluconeogenic pathway, which leads from phosphoenolpyruvate to glucose. Without this capacity, then, a cell or organism is unable to convert fuels or metabolites that are degraded to acetate (fatty acids and certain amino acids) into carbohydrates. In plants, certain invertebrates, and some microorganisms (including E. coli and yeast) acetate can serve both as an energy-rich fuel and as a source of phosphoenolpyruvate for carbohydrate synthesis. In these organisms, enzymes of the glyoxylate cycle catalyse the net conversion of acetate to succinate or other four-carbon intermediates of the citric acid cycle: In the glyoxylate cycle, acetyl-CoA condenses with oxaloacetate to form citrate, and citrate is converted to isocitrate, exactly as in the citric acid cycle. The next step, however, is not the breakdown of isocitrate by isocitrate dehydrogenase but the cleavage of isocitrate by isocitratelyase, forming succinate and glyoxylate. The glyoxylate then condenses with a second molecule of acetyl-CoA to yield malate, in a reaction catalysed by malate synthase. The malate is subsequently oxidized to oxaloacetate, which can condense with another molecule of acetyl-CoA to start another turn of the cycle (Fig. 6.12). Each turn of the glyoxylate cycle consumes two molecules of acetyl-CoA and produces one molecule of succinate, which is then available for biosynthetic purposes. The succinate may be converted through fumarate and malate into oxaloacetate Continue reading >>

Converting Carbohydrates To Triglycerides

Converting Carbohydrates To Triglycerides

Consumers are inundated with diet solutions on a daily basis. High protein, low fat, non-impact carbohydrates, and other marketing “adjectives” are abundant within food manufacturing advertising. Of all the food descriptors, the most common ones individuals look for are “fat free” or “low fat”. Food and snack companies have found the low fat food market to be financially lucrative. The tie between fat intake, weight gain, and health risks has been well documented. The dietary guidelines suggest to keep fat intake to no more than 30% of the total diet and to consume foods low in saturated and trans fatty acids. But, this does not mean that we can consume as much fat free food as we want: “Fat free does not mean calorie free.” In many cases the foods that are low in fat have a large amount of carbohydrates. Carbohydrate intake, like any nutrient, can lead to adverse affects when over consumed. Carbohydrates are a necessary macronutrient, vital for maintenance of the nervous system and energy for physical activity. However, if consumed in amounts greater than 55% to 65% of total caloric intake as recommended by the American Heart Association can cause an increase in health risks. According to the World Health Organization the Upper Limit for carbohydrates for average people is 60% of the total dietary intake. Carbohydrates are formed in plants where carbons are bonded with oxygen and hydrogen to form chains of varying complexity. The complexity of the chains ultimately determines the carbohydrate classification and how they will digest and be absorbed in the body. Mono-and disaccharides are classified as simple carbohydrates, whereas polysaccharides (starch and fiber) are classified as complex. All carbohydrates are broken down into monosaccharides before b Continue reading >>

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