on on Fats (or triglycerides) within the body are ingested as food or synthesized by adipocytes or hepatocytes from carbohydrate precursors ([link]). Lipid metabolism entails the oxidation of fatty acids to either generate energy or synthesize new lipids from smaller constituent molecules. Lipid metabolism is associated with carbohydrate metabolism, as products of glucose (such as acetyl CoA) can be converted into lipids. Lipid metabolism begins in the intestine where ingested triglycerides are broken down into smaller chain fatty acids and subsequently into monoglyceride molecules (see [link]b) by pancreatic lipases, enzymes that break down fats after they are emulsified by bile salts. When food reaches the small intestine in the form of chyme, a digestive hormone called cholecystokinin (CCK) is released by intestinal cells in the intestinal mucosa. CCK stimulates the release of pancreatic lipase from the pancreas and stimulates the contraction of the gallbladder to release stored bile salts into the intestine. CCK also travels to the brain, where it can act as a hunger suppressant. Together, the pancreatic lipases and bile salts break down triglycerides into free fatty acids. These fatty acids can be transported across the intestinal membrane. However, once they cross the membrane, they are recombined to again form triglyceride molecules. Within the intestinal cells, these triglycerides are packaged along with cholesterol molecules in phospholipid vesicles called chylomicrons ([link]). The chylomicrons enable fats and cholesterol to move within the aqueous environment of your lymphatic and circulatory systems. Chylomicrons leave the enterocytes by exocytosis and enter the lymphatic system via lacteals in the villi of the intestine. From the lymphatic system, the chylo Continue reading >>
Ch. 7 Nutrition
Sort a 30. Your roommate Demetrius is participating in a weightlifting course and complains of a burning pain during workouts. You explain to Demetrius that the rapid breakdown of glucose in his muscles produces large amounts of pyruvate, which leads to a fall in pH within the muscle and that the muscle responds by converting excess pyruvate to a. lactate. b. glycerol. c. acetyl CoA. d. amino acids. b 61. Which of the following accounts for the higher energy density of a fatty acid compared with the other energy-yielding nutrients? a. Fatty acids have a lower percentage of hydrogen-carbon bonds b. Fatty acids have a greater percentage of hydrogen-carbon bonds c. Other energy-yielding nutrients have a lower percentage of oxygen-carbon bonds d. Other energy-yielding nutrients undergo fewer metabolic reactions, thereby lowering the energy yield c 66. Which of the following is the most likely explanation for the body's higher metabolic efficiency of converting a molecule of corn oil into stored fat compared with a molecule of sucrose? a. The enzymes specific for metabolizing absorbed fat have been found to have higher activities than those metabolizing sucrose b. The absorbed corn oil is transported to fat cells at a faster rate than the absorbed sucrose, thereby favoring the uptake of corn oil fat c. There are fewer metabolic reactions for disassembling the corn oil and re-assembling the parts into a triglyceride for uptake by the fat cells d. Because corn oil has a greater energy content than sucrose, conversion of these nutrients into stored fat requires a smaller percentage of the energy from the corn oil a 69. Which of the following is a characteristic of the metabolism of specific macronutrients? a. The rate of fat oxidation does not change when fat is eaten in excess 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 >>
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). 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. 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 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 >>
The Catabolism Of Fats And Proteins For Energy
The Catabolism of Fats and Proteins for Energy Before we get into anything, what does the word catabolism mean? When we went over catabolic and anabolic reactions , we said that catabolic reactions are the ones that break apart molecules. To remember what catabolic means, think of a CATastrophe where things are falling apart and breaking apart. You could also remember cats that tear apart your furniture. In order to make ATP for energy, the body breaks down mostly carbs, some fats and very small amounts of protein. Carbs are the go-to food, the favorite food that cells use to make ATP but now were going to see how our cells use fats and proteins for energy. What were going to find is that they are ALL going to be turned into sugars (acetyl) as this picture below shows. First lets do a quick review of things you already know because it is assumed you learned cell respiration already and how glucose levels are regulated in your blood ! Glucose can be stored as glycogen through a process known as glycogenesis. The hormone that promotes this process is insulin. Then when glycogen needs to be broken down, the hormone glucagon, promotes glycogenolysis (Glycogen-o-lysis) to break apart the glycogen and increase the blood sugar level. Glucose breaks down to form phosphoglycerate (PGAL) and then pyruvic acid. What do we call this process of splitting glucose into two pyruvic sugars? Thats glycolysis (glyco=glucose, and -lysis is to break down). When theres not enough oxygen, pyruvic acid is converted into lactic acid. When oxygen becomes available, lactic acid is converted back to pyruvic acid. Remember that this all occurs in the cytoplasm. The pyruvates are then, aerobically, broken apart in the mitochondria into Acetyl-CoA. The acetyl sugars are put into the Krebs citric aci 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 >>
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 >>
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 >>
Breaking Down Fatty Acid Synthesis: Energy From Fat Stores
Fatty acids are important as a source of energy in our bodies. Knowing the effects from breaking down fatty acid synthesis and energy from fat stores is important to those who are dieting or working out. If you have an excess amount of glucose, another source of energy, in your system, this can easily be stored as fat as well. All of the cell membranes in the human body are made up of phospholipids, which have two different fatty acids in them. These fatty acids are used for protein modification, and the resulting metabolism of these fatty acids ends in the production of energy. How Your Body Uses Stored Fat When you are not eating, your body is not producing energy and it will rely on the stored energy in carbohydrates, fats and proteins. When this happens, certain organs in the body secrete hormones that have an effect on the liver, fat and muscle tissues. During this period your body is pulling energy from these sources and depleting them at the same time. Fat cells do not disappear, but they do get smaller as more energy is used. Fatty acids are stored in the body as triglycerides and are an important source of energy since they are both anhydrous, meaning that is contains no water, and reduced which has to do with the changing of the oxidation of an atom. The energy created from fatty acids is more than twice that of the same amount of carbohydrates. One gram of carbohydrates results in 4Kcal/g while the same amount of fatty acids delivers 9Kcal/g. Fat is an important and powerful means of storing energy just as they are a noticeable source of dietary calories. About 30-40% of calories, at least in the American diet, are from fat. As can be noted from this chart, fatty acids are excellent at storing energy that can later be used when needed: Fat: 100,000 Kcal Prote Continue reading >>
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 >>
Metabolism: Transformations and Interactions Chemical Reactions in the Body Plants use the sunâ€™s energy to make carbohydrate from carbon dioxide and water. This is called photosynthesis. Humans and animals eat the plants and use the carbohydrate as fuel for their bodies. During digestion, the energy-yielding nutrients are broken down to monosaccharides, fatty acids, glycerol, and amino acids. After absorption, enzymes and coenzymes can build more complex compounds. In metabolism they are broken down further into energy (ATP), water and carbon dioxide. Chemical Reactions in the Body Metabolic reactions take place inside of cells, especially liver cells. Anabolism is the building up of body compounds and requires energy. Catabolism is the breakdown of body compounds and releases energy. Chemical Reactions in the Body Enzymes and coenzymes are helpers in reactions. Enzymes are protein catalysts that cause chemical reactions. Coenzymes are organic molecules that function as enzyme helpers. Cofactors are organic or inorganic substances that facilitate enzyme action. Breaking Down Nutrients for Energy The breakdown of glucose to energy starts with glycolysis to pyruvate. Pyruvate may be converted to lactic acid anaerobically (without oxygen) and acetyl CoA aerobically (with oxygen). Eventually, all energy-yielding nutrients enter the TCA cycle or tricarboxylic acid cycle (or Krebâ€™s cycle) and the electron transport chain. Breaking Down Nutrients for Energy Glucose Glucose-to-pyruvate is called glycolysis or glucose splitting. Pyruvateâ€™s Options Anaerobic â€“ lactic acid Aerobic â€“ acetyl CoA Pyruvate-to-Lactate Oxygen is not available or cells lack sufficient mitochondria Lactate is formed when hydrogen is added to pyruvate. Liver cells recycle 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 >>
The Catabolism Of Fats And Proteins For Energy
Before we get into anything, what does the word catabolism mean? When we went over catabolic and anabolic reactions, we said that catabolic reactions are the ones that break apart molecules. To remember what catabolic means, think of a CATastrophe where things are falling apart and breaking apart. You could also remember cats that tear apart your furniture. In order to make ATP for energy, the body breaks down mostly carbs, some fats and very small amounts of protein. Carbs are the go-to food, the favorite food that cells use to make ATP but now we’re going to see how our cells use fats and proteins for energy. What we’re going to find is that they are ALL going to be turned into sugars (acetyl) as this picture below shows. First let’s do a quick review of things you already know because it is assumed you learned cell respiration already and how glucose levels are regulated in your blood! Glucose can be stored as glycogen through a process known as glycogenesis. The hormone that promotes this process is insulin. Then when glycogen needs to be broken down, the hormone glucagon, promotes glycogenolysis (Glycogen-o-lysis) to break apart the glycogen and increase the blood sugar level. Glucose breaks down to form phosphoglycerate (PGAL) and then pyruvic acid. What do we call this process of splitting glucose into two pyruvic sugars? That’s glycolysis (glyco=glucose, and -lysis is to break down). When there’s not enough oxygen, pyruvic acid is converted into lactic acid. When oxygen becomes available, lactic acid is converted back to pyruvic acid. Remember that this all occurs in the cytoplasm. The pyruvates are then, aerobically, broken apart in the mitochondria into Acetyl-CoA. The acetyl sugars are put into the Krebs citric acid cycle and they are totally broken 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 >>
Nutrition Ch. 7
• ATP (transfer of energy in reactions) o one of the main energy-storage molecules: only form of energy that can be used directly by cells to do work they need to do o Made up of 3 phosphate groups o add water - Hydrolysis of its phosphate groups generates energy • Provides energy that powers living cell activity • Body captures and releases energy in bonds of ATP o Involved in coupled reactions • coupled reactions: hydrolysis at time body needs energy • Body converts chemical energy of food to chemical energy of ATP -when used, called ADP • Pyruvate #1 → lactate - When body needs energy quickly, but energy doesn't last long (couple of minutes) - Anaerobic (no oxygen) - Pyruvate accepts hydrogen - Occurs even a little at rest - During intense exercise, lactate accumulates in muscles and causes blood pH drop, burning pain, and fatigue - Liver can convert lactate to glucose - called Cori cycle (recycling process) o Pyruvate → acetyl CoA • When body expends energy more slowly, but energy sustained for longer (greater total energy yield) • Aerobic (requires oxygen) • Carbon group removed from 3-carbon pyruvate → 2-carbon compound → bonds with CoA → acetyl CoA • Produces carbon dioxide • Not reversible pathway • Much more ATP produced than glycolysis • Amino acids o Amino acid deamination occurs (lose their nitrogen-containing amino group) o Amino acid pathways: • Some amino acid → pyruvate -- Can provide glucose • Some amino acid → acetyl CoA -- Can provide additional energy or make body fat (but not glucose) • Some amino acid enter TCA cycle directly as compounds -- Can generate energy in cycle -- Can generate glucose Continue reading >>