Metabolism and Energetics: Key Terms and Concepts

Metabolism and Energetics

Introduction

This unit covers the essential vocabulary and concepts related to metabolism and energetics, which are foundational topics in anatomy and physiology. Understanding these terms is crucial for describing how the body obtains, transforms, and utilizes energy at the cellular and systemic levels.

Key Concepts in Metabolism

• Metabolism: The sum of all chemical reactions that occur within a living organism to maintain life, including both anabolic (building up) and catabolic (breaking down) processes.

• Cellular metabolism: The set of metabolic reactions and processes that take place in the cells to convert nutrients into energy and building blocks for macromolecules.

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input.

• Metabolic turnover: The continuous breakdown and synthesis of cellular components.

• Nutrient pool: The reserve of nutrients available for metabolic processes in the body.

Energy Pathways

• Glycolysis: The anaerobic process of breaking down glucose into pyruvate, yielding ATP and NADH.

• Anaerobic metabolism: Energy production in the absence of oxygen, primarily through glycolysis.

• Aerobic metabolism: Energy production in the presence of oxygen, involving the citric acid cycle and electron transport chain.

• Citric acid cycle (Krebs cycle): A series of enzyme-catalyzed reactions in the mitochondria that generate high-energy electron carriers from acetyl CoA.

• Acetyl CoA (acetyl coenzyme A): A central molecule in metabolism that enters the citric acid cycle.

• Coenzyme: Non-protein compounds that assist enzymes in catalyzing reactions (e.g., NAD, FAD).

• NAD (nicotinamide adenine dinucleotide): An electron carrier involved in redox reactions.

• FAD (flavin adenine dinucleotide): Another electron carrier used in the citric acid cycle and electron transport chain.

• Electron transport system (ETS): A series of protein complexes in the mitochondrial membrane that transfer electrons and produce ATP.

• Oxidative phosphorylation: The process of ATP formation as electrons are transferred to oxygen in the ETS.

• Cytochromes: Proteins in the ETS that transfer electrons.

• ATP synthase: The enzyme that synthesizes ATP from ADP and inorganic phosphate, powered by a proton gradient.

• Chemiosmosis: The movement of ions across a semipermeable membrane, generating ATP.

Carbohydrate Metabolism

• Glycogenesis: The formation of glycogen from glucose for storage in the liver and muscles.

• Glycogenolysis: The breakdown of glycogen to release glucose.

• Gluconeogenesis: The synthesis of glucose from non-carbohydrate sources, such as amino acids.

• Salivary amylase, Pancreatic alpha-amylase: Enzymes that break down starches into simpler sugars.

• Maltase, Sucrase, Lactase: Enzymes that digest disaccharides into monosaccharides.

• Flatus: Gas produced by bacterial fermentation of undigested carbohydrates in the intestine.

• Carrier protein: Proteins that transport substances across cell membranes.

• Pyruvate: The end product of glycolysis, which can enter aerobic or anaerobic pathways.

Lipid Metabolism

• Lingual lipase, Pancreatic lipase: Enzymes that break down dietary fats into fatty acids and glycerol.

• Bile salts: Compounds that emulsify fats, aiding in their digestion and absorption.

• Emulsification: The process of breaking large fat globules into smaller droplets.

• Micelles: Small transport carriers in the intestine that enable absorption of lipids.

• Chylomicrons, Lipoproteins: Complexes that transport lipids in the blood.

• Lipoprotein lipase: Enzyme that breaks down triglycerides in lipoproteins.

• LDL, VLDL, HDL: Types of lipoproteins classified by density; involved in cholesterol transport.

• Lipolysis: The breakdown of triglycerides into fatty acids and glycerol.

• Beta-oxidation: The process of breaking down fatty acids for energy in the mitochondria.

• Essential fatty acid: Fatty acids that must be obtained from the diet.

• Lipogenesis: The synthesis of fatty acids from acetyl CoA.

Protein Metabolism

• Pepsin, Enteropeptidase, Proenzyme, Trypsinogen, Trypsin, Chymotrypsin, Carboxypeptidase, Elastase: Enzymes involved in protein digestion.

• Peptidases, Dipeptidases: Enzymes that further break down peptides into amino acids.

• Essential amino acid: Amino acids that cannot be synthesized by the body and must be obtained from the diet.

• Amination, Transamination, Deamination: Processes involved in amino acid metabolism and the removal or transfer of amino groups.

• Urea, Urea cycle: The process by which ammonia is converted to urea for excretion.

Metabolic States and Disorders

• Absorptive state: The period following a meal when nutrients are being absorbed and used for energy or storage.

• Postabsorptive state: The period when the digestive tract is empty and the body relies on stored nutrients.

• Ketone bodies, Ketoacidosis, Ketosis: Compounds produced during fat metabolism; excessive accumulation can lead to metabolic acidosis.

• Protein deficiency disease (Kwashiorkor): A condition caused by inadequate protein intake.

• Gout, Uric acid, Gouty arthritis: Disorders related to the accumulation of uric acid crystals in joints.

• Nitrogenous wastes: Waste products from protein metabolism, primarily urea and uric acid.

Nutrition and Energetics

• Nutrition: The process of obtaining and using food for growth, metabolism, and repair.

• Vitamins, Minerals: Essential nutrients required in small amounts for various physiological functions.

• Fat-soluble vitamins, Water-soluble vitamins: Classification based on solubility; affects absorption and storage.

• Hypovitaminosis, Hypervitaminosis: Deficiency or excess of vitamins, respectively.

• Intrinsic factor: A protein necessary for vitamin B12 absorption.

• Balanced diet, Malnutrition: Adequate vs. inadequate intake of essential nutrients.

• Calorie vs. calorie, Kilocalorie: Units of energy; 1 kilocalorie (kcal) = 1,000 calories.

• Complete proteins, Incomplete proteins: Proteins containing all essential amino acids vs. those lacking one or more.

• Eating disorders (Anorexia, Anorexia nervosa, Bulimia, Obesity): Conditions affecting food intake and body weight.

• Regulatory obesity, Metabolic obesity: Obesity due to behavioral vs. metabolic causes.

• Phenylketonuria (PKU): A genetic disorder affecting amino acid metabolism.

Energetics and Thermoregulation

• Energetics: The study of energy flow and transformation in biological systems.

• Basal metabolic rate (BMR): The rate of energy expenditure at rest.

• Thermoregulation: The maintenance of body temperature within a normal range.

• Feeding center, Satiety center: Hypothalamic centers that regulate hunger and fullness.

• Neuropeptide Y (NPY), Ghrelin, Leptin: Hormones and peptides involved in appetite regulation.

• Radiation, Evaporation, Convection, Conduction: Mechanisms of heat transfer in the body.

• Insensible perspiration, Sensible perspiration: Types of water loss through the skin.

• Heat-loss center, Heat-gain center: Hypothalamic centers that regulate body temperature.

• Vasodilation, Blood shunting, Sweat production, Respiratory heat loss: Physiological responses to regulate heat loss or retention.

• Nonshivering thermogenesis, Shivering thermogenesis: Mechanisms of heat production in the body.

Example: ATP Production in Mitochondria

The mitochondrion is the site of aerobic metabolism, where the citric acid cycle and electron transport system generate ATP. The process of oxidative phosphorylation couples the transfer of electrons to the synthesis of ATP via ATP synthase.

Key Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$

Additional info: The above equation summarizes aerobic cellular respiration, which is the primary method of ATP production in most eukaryotic cells.