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Notes on Metabolism: Transformations and Interactions - Nutrition | NUFS 2110, Study notes of Dietetics

chapter 7 Material Type: Notes; Professor: Oates; Class: Elementary Nutrition; Subject: Nutrition and Foods; University: Tennessee State University; Term: Spring 2011;

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2010/2011

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Download Notes on Metabolism: Transformations and Interactions - Nutrition | NUFS 2110 and more Study notes Dietetics in PDF only on Docsity! Chapter 7 – Metabolism: Transformations and Interactions Chapter 7 Review I. Chemical Reactions in the Body Plants use the sun’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. A. Metabolic reactions take place inside of cells, especially liver cells. B. Anabolism is the building up of body compounds and requires energy. C. Catabolism is the breakdown of body compounds and releases energy. D. The Transfer of Energy in Reactions—ATP 1. A high-energy compound called adenosine triphosphate (ATP) is made. 2. Coupled reactions are chemical reactions that occur simultaneously. E. Enzymes and coenzymes are helpers in reactions. 1. Enzymes are protein catalysts that cause chemical reactions. 2. Coenzymes are organic molecules that function as enzyme helpers. 3. Cofactors are organic or inorganic substances that facilitate enzyme action. II. 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 Kreb’s cycle) and the electron transport chain. A. Glucose 1. Glucose-to-pyruvate is called glycolysis or glucose splitting. 2. Pyruvate’s Options a. Anaerobic – lactic acid b. Aerobic – acetyl CoA 3. Pyruvate-to-Lactate a. Oxygen is not available or cells lack sufficient mitochondria b. Lactate is formed when hydrogen is added to pyruvate. c. Liver cells recycle muscle lactic acid through the Cori cycle. 4. Pyruvate-to-acetyl CoA is irreversible. 5. Acetyl CoA’s Options a. Synthesize fats when the body has enough ATP b. Generate ATP when the cell is low in energy B. Glycerol and Fatty Acids 1. The conversion of glycerol to pyruvate is easy because they are both three-carbon compounds. 2. Fatty acids-to-acetyl CoA reactions are called fatty acid oxidation. 3. Fatty acids cannot be used to synthesize glucose. Glucose must be available to provide energy to the red blood cells, brain, and nervous system. C. Amino Acids 1. Amino acids can be concerted to acetyl CoA after deamination. 2. Amino Acids-to-Glucose – a fairly good source of glucose when carbohydrate is not available 3. Deamination results in two products: a. Keto acid b. Ammonia 4. Transamination is the transfer of the amino group from an amino acid to a keto acid. 5. Ammonia is converted to urea—a much less toxic compound—in the liver. 6. Urea is excreted through the kidneys to rid the body of unused nitrogen. D. Breaking Down Nutrients for Energy—In Summary 1. Glucose and fatty acids are primarily used for energy, amino acids to a lesser extent. 2. Glucose is made from all carbohydrates, most amino acids and the glycerol portion of fat. 3. Protein is made from amino acids. 4. Glucose can be made into nonessential amino acids if nitrogen is present. 5. All energy-yielding nutrients consumed in excess can contribute to fat storage. E. The Final Steps of Catabolism 1. The TCA cycle contains a 4-carbon compound called oxaloacetate that has a critical role. 2. The Electron Transport Chain a. Consumes oxygen b. Produces carbon dioxide and water c. Produces energy as ATP 3. The kCalories-per-Gram Secret Revealed a. Fat provides 9 kcal/gram. b. Carbohydrate provides 4 kcal/gram. c. Protein provides 4 kcal/gram. d. Fat provides more energy because the bonds in fat molecules are easily oxidized and result in more ATP. III. Energy Balance When energy intake exceeds energy output, there is a gain in weight. Excess energy can come from protein, fat or carbohydrate. Fat is the most efficient in being stored as fat. A. Feasting—Excess Energy 1. Excess protein is converted to fat but this is inefficient and indirect. Its priority is other roles. 2. Excess carbohydrate is converted to fat but this is inefficient and indirect. Its priority is glycogen stores. 3. Excess fat is efficiently converted to fat. B. The transition from feasting to fasting draws on reserves. C. Fasting—Inadequate Energy 1. Glucose Needed for the Brain 2. Protein Meets Glucose Needs 3. The Shift to Ketosis a. Ketones are produces when glucose is not available. 4. Ketosis causes a suppression of the appetite. 5. Slowing of Metabolism 6. Symptoms of Starvation a. Muscle wasting b. Decreased heart rate, respiratory rate, metabolic rate, and body temperature c. Impaired vision d. Organ failure e. Decreased immunity f. Depression, anxiety, and food-related dreams IV. Highlight: Alcohol (ethyl alcohol, ethanol) and Nutrition The metabolism of alcohol is handled differently in the body. Alcohol interferes with metabolism and impairs health and nutrition. There are potential health benefits to consuming moderate amounts of alcohol. A. Alcohol in Beverages 1. Beer, wine and distilled liquor (hard liquor) 2. Alcohol behaves like a drug, therefore altering body functions. 3. Moderation of drinks a. 5 ounces of wine b. 10 ounces of wine cooler c. 12 ounces of beer d. 1 ½ ounces distilled liquor (80 proof) B. Alcohol in the Body 1. Quickly absorbed 2. Carbohydrates decrease the absorption of alcohol. 3. Alcohol dehydrogenase breaks down alcohol in the stomach. 4. Women absorb more alcohol then men. C. Alcohol Arrives in the Liver 1. Accumulation of fatty acids 2. Alcohol dehydrogenase breaks down alcohol to acetaldehyde. 3. Alcohol abuse has damaging effects. 4. Coenzyme NAD D. Alcohol Disrupts the Liver 1. Development of a fatty liver is the first stage of liver deterioration. 2. Fibrosis is the second stage. 3. Cirrhosis is the most advanced stage of liver deterioration. 4. Microsomal ethanol-oxidizing system (MEOS) metabolizes alcohol and drugs. E. Alcohol Arrives in the Brain 1. Alcohol acts as a narcotic, anesthetizes pain 2. Alcohol suppresses antidiuretic hormone (ADH) resulting in the loss of body water. F. Alcohol and Malnutrition
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