Animal Physiology II Lecture Notes - SC/BIOL 3070

ANIMAL PHYSIOLOGY II SC/BIOL 3070 - 4.0 Metabolism Suggested readings: Sherwood et al. pgs. 297-323 and 715-722 Metabolism 1 Outline Learning Objectives: Introduction: anabolism vs. catabolism Carbohydrate, lipid and protein metabolism Metabolic rate (MR) Factors affecting metabolic rate (e.g. size,...

ANIMAL PHYSIOLOGY II SC/BIOL 3070 - 4.0 Metabolism Suggested readings: Sherwood et al. pgs. 297-323 and 715-722 Metabolism 1 Outline Learning Objectives: Introduction: anabolism vs. catabolism Carbohydrate, lipid and protein metabolism Metabolic rate (MR) Factors affecting metabolic rate (e.g. size, activity, temperature, hormones) Metabolism 2 Introduction Metabolism: - the sum total of all the chemical reactions occurring in an organism ➨ balance between two main metabolic pathways: 1) anabolic (synthesis) reactions ➨ chemical reactions that combine simple, smaller molecules into more complex ones - uses energy - e.g. protein formation from amino acids; carbohydrate formation from simple sugars Metabolism 3 Introduction Metabolism: - the sum total of all the chemical reactions occurring in an organism ➨ balance between two main metabolic pathways: 2) catabolic (breakdown) reactions ➨ chemical reactions that break down complex energy-rich molecules into simpler ones - releases energy - e.g. proteins are broken down by various proteases, etc. Metabolism 4 Introduction Summary of Anabolism and Catabolism of Organic Nutrients: Fig. 7-23, p313 Metabolism 5 Carbohydrate metabolism Carbohydrate Catabolism: - breakdown of carbohydrates into smaller units (i.e. glucose) ➨ free energy released is used to form high-energy compounds (e.g. ATP, NADH) - if glucose is immediately needed to supply energy, it is broken down by glycolysis to generate ATP and pyruvic acid ➨ pyruvic acid can enter Krebs cycle to generate more ATP, as well as NADH that is oxidated in the electron transport chain for more ATP energy Metabolism 6 Carbohydrate metabolism Carbohydrate Catabolism: - if blood glucose levels are low and energy is needed, glycogen stored in the liver and muscles can be broken down by glycogenolysis providing free glucose for ATP generation glycogenolysis Metabolism 7 Carbohydrate metabolism Carbohydrate Anabolism: - if blood glucose levels exceed cellular need for ATP synthesis, glycogen can be formed from glucose by process of glycogenesis in liver and muscles glycogenesis Metabolism 8 Carbohydrate metabolism Carbohydrate Anabolism: - gluconeogenesis: conversion of non-carbohydrate precursors (i.e. fat or protein molecules) into glucose - e.g. glycerol derived from hydrolysis of triglycerides (i.e. fats) can contribute to gluconeogenesis - some amino acids can be catabolized to pyruvate, which can then be used in gluconeogenesis ➨ occurs during fasting or starvation ➨ major sites of gluconeogenesis are the liver and kidney Metabolism gluconeogenesis 9 Lipid metabolism Lipid Anabolism: - lipogenesis: conversion of glucose or amino acids into triglycerides ➨ intermediary link in lipogenesis (red arrows) is acetyl CoA ➨ occurs when cellular ATP and glucose levels are high glycolysis lipogenesis Metabolism triglyceride molecule 10 Lipid metabolism Lipid Catabolism: - lipolysis: when triglycerides are released from fat deposits and split into fatty acids and glycerol, which are then catabolized separately lipolysis Metabolism beta oxidation: breakdown of fatty acids to acetyl CoA, which enters Krebs cycle to generate energy (i.e ATP) 11 Lipid metabolism Lipid Catabolism: - ketogenesis: process where fatty acids are catabolized into acetyl CoA molecules by beta oxidation, and subsequently are converted into ketone bodies that can be used as an energy source by brain, heart muscle, kidney ➨ occurs when blood glucose levels are low or during diabetic states (i.e. blood glucose is high, but cannot be taken up by cells), or following a high-fat diet ➨ ketone bodies are acidic!!! - too much ketogenesis can quickly make blood very acidic ➨ e.g. diabetic ketoacidosis results from insulin shortage Metabolism 12 Protein metabolism Protein Catabolism: - amino acid catabolism occurs mainly in the liver and involves deamination, i.e. removal of the amino (-NH2) group by enzymes called deaminases ➨ resulting “carbon skeletons” can be entered into glycolytic or Krebs cycle pathways for energy production ➨ alternatively, can be used to synthesize new amino acids, glucose (gluconeogenesis) or triglycerides (lipogenesis) ➨ amino group is joined with CO2 to form the nitrogenous waste urea generic amino acid Metabolism 13 Protein metabolism Protein Anabolism: - amino acid synthesis involves amination (i.e. addition of ammonia) to components of glycolytic or Krebs cycle pathways via enzymes called transaminases Metabolism 14 Relationship between Anabolism and Catabolism Metabolism 15 Metabolic rate (MR) MR = rate at which energy is expended ➨ expressed as heat energy released per unit time Basal metabolic rate (BMR) ➨ term applied to endotherms ➨ stable rate of energy metabolism at rest (i.e. in a neutrally temperate environment with minimal physiological stress and after fasting) ➨ energy used in this state is sufficient only for vital functioning (e.g. heart, lungs, kidneys etc.) Standard metabolic rate (SMR) ➨ term applied to ectotherms ➨ an animal’s resting and fasting metabolism at ‘preferred’ ambient temperature Metabolism 16 Metabolic rate (MR) Why is it important to know an animal’s MR? ➨ main determinant of how much food an animal requires ➨ provides a quantitative measurement of the total activity of all physiological processes ➨ determines the rate that animals use resources from an ecosystem Metabolism Fig. 15-1, p717 17 Factors influencing metabolic rate 1) body size - metabolic rate is inversely related to body size ➨ i.e. the smaller the animal, the higher the relative metabolic rate per gram of body tissue Why???? ➨ smaller animals have a greater surface area to volume ratio ➨ smaller animals lose more heat to the environment per unit time Fig. 15-3b, p721 Metabolism 18 Factors influencing metabolic rate 1) body size 6x body weight/week ➨ to maintain a constant body temperature, despite rapid heat lost across the body surface, a small animal must metabolize food at a high rate 0.33x body weight/week Metabolism 19 Factors influencing metabolic rate 2) locomotion - amount of energy required (beyond BMR) to move a unit of mass of an animal a unit distance ➨ small animals use more energy to achieve a given velocity of locomotion compared to larger animals Fig. 15-4a, p723 Metabolism 20 Factors influencing metabolic rate 3) environmental (ambient) temperature -in endotherms: metabolic rate lowest in thermoneutral zone (TNZ), but elevates above or below the TNZ - in ectotherms: metabolic rate increases at higher temperature and decreases at lower temperature TNZ Metabolism 21 Factors influencing metabolic rate 3) environmental (ambient) temperature - metabolic rate is only increased proportionally to change in temperature up to a limit ➨ Beyond these limits results in death of the animal thermogenesis evaporative cooling TNZ Similar to Fig. 15-21, p749 Metabolism 22 Factors influencing metabolic rate 4) hormones - insulin - glucagon - epinephrine - glucocorticoids - thyroid hormone Metabolism 23