HUN1201 LECTURE NOTES CHAPTER 7 Metabolism From Food to Life Metabolism Metabolism is the sum of all chemical and physical processes by which the body breaks down and builds up molecules Calorimeter measures a food s caloric content Anabolism is the process of making larger chemically complex molecules Critical for growth repair maintenance and synthesis of chemical products essential for human functioning Anabolism from smaller ones Requires energy Catabolism Catabolism breakdown of larger complex molecules to smaller more basic ones Begins with digestion chemical reactions break down proteins lipids carbohydrates Old cells or tissues are broken down for repair or replacement Releases energy Adenosine Triphosphate ATP ATP is an organic compound used by cells as a source of energy Potential energy is stored in the high energy phosphate bonds When bonds are broken energy is released This energy is used to keep cells functioning Mitochondria is the primary site of chemical energy ATP production Metabolic Enzymes Enzymes mediate chemical reactions Coenzymes are non protein substances necessary for enzyme activity FAD FADH2 and vitamins function as coenzymes Cofactors are typically minerals required for enzyme activity Iron magnesium and zinc function as cofactors Energy from Carbohydrates When glucose is transported to the liver it is Phosphorylated and metabolized for energy or stored as glycogen Released into circulation for other cells to use as fuel or stored as glycogen muscle tissue Converted to fatty acids if glucose exceeds energy needs and stored as triglycerides in adipose tissue Fructose and galactose are converted to glucose in the liver and follow the same process Glycolysis Occurs in the cytosol Anaerobic reaction Energy from fat Lipolysis triglycerides are broken down by lipase to yield 1 glycerol and 3 fatty acids Glycerol is converted to pyruvate then to acetyl CoA for entry into the TCA cycle Fatty acids FAs are used for energy Ketone Synthesis Ketones are by products of fat catabolism Ketosis occurs when ketones acidic inappropriately lower blood pH Ketoacidosis occurs when blood pH falls further resulting in severe dehydration Energy from Protein The body preferentially uses fat and carbohydrate as fuel sources Protein is saved for metabolic functions that cannot be performed by other compounds Protein is used for fuel primarily when total energy or carbohydrate intake is low Proteolysis dietary proteins are digested into amino acids or small peptides Amino acids are transported to the liver Made into proteins Released into the blood for uptake by other cells for building and repair functions Excess dietary protein Used for energy or stored as triglycerides During starvation the body turns to its own tissues for energy Ammonia from amino acid deamination Used as nitrogen source for synthesis of nonessential amino acids High levels are toxic Liver converts ammonia to less toxic urea Alcohol Oxidation Alcohol is oxidized primarily in the liver by enzymes Alcohol dehydrogenase ADH Aldehyde dehydrogenase ALDH Microsomal ethanol oxidizing system MEOS First pass metabolism small amount of alcohol is oxidized in the stomach before being absorbed into the bloodstream Gastric ADH activity Reduces alcohol absorption Genetic differences in amount of activity Alcohol Absorption Most is absorbed into the blood and transported to be oxidized by the liver Liver typically oxidizes alcohol at a constant rate about 1 drink per hour This rate varies with the individual s genetic profile state of health body size use of medication and nutritional status Excess alcohol goes back into the blood Stored Energy Stored energy can be used during times of sleep fasting or exercise Extra energy is stored as Carbohydrate in limited amounts as liver and muscle glycogen Fat triglycerides in unlimited amounts Synthesizing Macronutrients Gluconeogenesis making new glucose from nonglucose substrates glucogenic amino acids primarily glycerol triglyceride Maintains blood glucose during sleep fasting trauma and exercise Protein catabolism for glucose production can draw on vital tissue proteins skeletal and heart muscles and organ proteins Lipogenesis de novo synthesis making fat from nonfat substances such as carbohydrates amino acids and alcohol When consuming excess calories acetyl CoA units form fatty acid chains Fatty acids combine with glycerol to form triglycerides Mostly occurs in liver cells Amino acid synthesis NEAA The body makes the carbon skeleton of nonessential amino acids Amine group comes from transamination Synthesis of NEAA occurs only when the body has enough energy and nitrogen Since essential amino acids cannot be synthesized they must be consumed Hormones regulate metabolism Insulin is the primary anabolic hormone Increases in the blood after a meal Activates storage enzymes Signals cellular uptake of glucose fatty acids and amino acids Glucagon epinephrine and cortisol are catabolic hormones Trigger the breakdown of stored triglycerides glycogen and body protein for energy Metabolic responses to feeding acids Anabolic state bloodstream enriched with glucose fatty acids and amino Glucose stored as glycogen Glycogen stores are saturated remaining glucose is stored as triglycerides Fatty acids are stored as triglycerides mostly in adipose tissues Amino acids are deaminated and carbon skeletons are converted to fatty acids for storage as triglycerides Metabolic responses to fasting Liver glycogen is broken down Blood glucose released Most cells can switch to using fatty acids as fuel to conserve glucose for brain and other cells that rely on glucose as fuel Ketones form as acetyl CoA units are blocked from entering TCA cycle Glycogenesis glucogenic amino acids and glycerol Metabolic responses to starvation The body shifts to survival mode Blood glucose is maintained to support brain and red blood cells Decline in activity body temperature and resting metabolic rate Fatty acids become the primary fuel Brain cells start to use ketone bodies Muscle protein supplies glucose
View Full Document
Unlocking...