Nutr 470 1st edition Lecture 23 Current Lecture• Introduction – Energy Metabolism• Energy is generated from food.• The reducing equivalents (2H) are collected by the respiratory chain for oxidation and coupled generation of ATP.• Energy balance (homeostasis)• Energy (food) intake• Energy expenditure• Malnutrition or undernutrition• Imbalance of energy• Overnutrition• Basic Concepts of DRIs• AIs: Adequate Intakes• Levels of nutrient intake judged based on less conclusive scientific information than are the RDAs. • RDAs: Recommended Dietary Allowances• Levels of essential nutrient intake judged to be adequate to meet the known nutrient needs.• RDA of carbohydrate is 130 g/day, which is lowand based on the amount of glucose needed by the brain.• Definition— Glycemic index is a measure of the extent to which carbohydrate and carbohydrate containing foods increase glucose levels.• Recommendations for Carbohydrates• The extent to which blood glucose is raised by a 50-g portion of a carbohydrate-containing food compared to 50 g of glucose. • Diets providing low glycemic index carbohydrates can improve blood glucose control in people with diabetes, as well as reduce elevated levels of blood cholesterol and triglycerides; have many benefits.• High fiber diets reduce the rates of glucose absorption and may help prevent cardiovascular• diseases.• Low carbohydrate and/or high fiber diets are considered as healthy foods• High fiber diets may reduce the risk of colon cancer.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Digestion of Carbohydrates• Maltase— dividing maltose into glucose + glucose• Sucrase— dividing sucrose into glucose + fructose• Lactase— dividing lactose into glucose + galactose• Final digestion products of carbohydrates are glucose, galactose, and fructose.• Endogenous Glucose Production• Why only the liver and the kidney, but not other organs, generate glucose?• Gluconeogenesis, Glycogen breakdown —> G-6-P• Glucose-6-phosphatase is the only enzyme that hydrolyzes glucose-6-phosphate to produce glucose.• Glucose-6-phosphatase is only present in the liver, kidney, and small intestine (?).• Significance of Glucose Transporters• GLUT2— allows rapid uptake or release of glucose liver cells and pancreatic β cells• GLUT4 is insulin-sensitive• The response of GLUT4 to insulin is crucial for the maintenance of glucose homeostasis. • Glucose• Glycolytic Pathway • HK/GK: hexokinase/glucokinase• HK/GK catalyze the phosphorylation of glucose as the first step of glycolysis• 6PFK1 catalyzes the rate-limiting step of glycolysis• F-2,6-P2 is the most powerful activator of• ATP is generated at two steps of glycolysis• 6PFK1: 6-phosphofructo-1-kinase• Gluconeogenesis• Gluconeogenesis (GNG) is the biosynthesis of new glucose.• FBPase catalyzes the rate-limiting step of GNG.• FBPase F-2,6-P2 is the most powerful inhibitor of FBPase.• GNG is the generation of GLUCOSE whereas G6Pgenesis is the generation of G6P.• Cooperative Regulation in the Liver• Hepatic 6PFK2/FBP2 exemplifies how fasting/feeding regulates fuel metabolism at the molecular level• Reactions of TCA Cycle• The synthesis of Citrate is catalyzed by citrate synthase• Citrate is isomerized to isocitrate by aconitase• First oxidative decarboxylation. • Second oxidative decarboxylation. • Substrate-level phosphorylation• Regeneration of oxaloacetate• Coordination in Glycogenolysis and Glycogenesis• When glucose levels are high— Promoting glucose storage • When glucose levels are low— Promoting glucose production from the liver• Glycogenesis and glycolysis is regulated in a coordinate pattern— Rapid regulation of glucose homeostasis.• Coordination in Glycogenolysis and Gluconeogenesis • When glucose levels are high—decrease of Glycogenolysis• When glucose levels are low— increase of Glycogenolysis• Fats come in two basic types.• Saturated fats• Unsaturated fats• Unsaturated fatty acids are of similar form.• cis fats• trans fats • Essential fatty acids must be supplied in the diet.• Linoleic acid a-Linolenic acid• Dietary Reference Intakes for Lipid• There is no RDA or AI for total fat.• There is an Acceptable Macronutrient Distribution Range (AMDR) for total fat – 20% ~35%• Less then the low end: high CHO• Higher than the high end: high fat• Hydrolysis of Triglycerides• Lipid digestion – intestine lumen• Pancreatic lipase hydrolyzes triglycerides in the form of micelles. Free fatty acids enter into the enterocytes by simple diffusion.• Lipid transport – circulation • Lipoprotein lipase hydrolyzes triglycerides in forms of CM and VLDL.• Lipolysis – fat cell• Lipogenesis• De novo synthesis of fatty acids occurs in the cytosol.• Source of acetyl-CoA• Acetyl-CoA – brought into cytosol through citrate-pyruvate cycle.• NADPH – generated after conversion of OAA to malate by malic enzyme• NADPH – generated from pentose phosphate shunt• Key Reactions of Lipogenesis• Acetyl-CoA —> —> Malonyl-CoA• ACC is the most important enzyme in the regulation of lipogenesis.• Acetyl-CoA carboxylase (ACC) catalyzes the generation of malonyl-CoA as the first step of• lipogenesis.• Regulation of Lipolysis• The rates of release of free fatty acids from adipose tissue are subjected to the regulation by hormones. • Hormones that favor lipolysis• Glucagon• Epinephrine and norepinephrine• Glucocorticoids• These hormones activate HSL.• The rates of release of free fatty acids from adipose tissue are subjected to the regulation by hormones. • Hormone that suppresses lipolysis• Insulin is the most powerful anti-lipolytic hormone.• A principal action of insulin in adipose tissue is to inhibit the activity of hormonesensitive• lipase (HSL).• Reactions of Fatty Acid Oxidation• The rates of release of free fatty acids from adipose tissue are subjected to the regulation by hormones. • Transferring acyl-CoA into mitochondria is the rate-limiting step of beta oxidation.• Carnitine palmitoyltransferase 1• CPT1, present in the out mitochondrial membrance, converts long chain acylCoA to acylcarnitine.• Inside mitochondrial matrix, CPT2 converts acylcarnitine back to acyl-CoA.• Ketogenesis•