Metabolism and Energetics

Metabolism and Energetics

  • Definition of Metabolism and Energetics

    • Metabolism refers to the set of life-sustaining chemical reactions that occur within cells, utilizing oxygen, nutrients, water, vitamins, minerals, organic substrates, and ions.

    • It is responsible for energy transformation to perform essential cellular functions.

Functions of Metabolism

  • Anabolism

    • The process of building larger molecules from smaller units.

    • This is an uphill process that requires energy input to form new chemical bonds.

  • Catabolism

    • The process of breaking down molecules to release energy.

    • Releases energy generally in the form of ATP, and includes oxidation-reduction reactions (redox reactions).

    • In a redox reaction:

    • A reduced atom or molecule gains energy.

    • An oxidized atom or molecule loses energy.

Energy Release and Utilization

  • Energy is often lost as heat during metabolic reactions, but some energy is available for:

    • Performing physical work

    • Performing chemical work

Oxidation-Reduction Reactions

  • Role of Electrons

    • Electrons carry chemical energy; in redox reactions, there is a transfer of electrons.

    • Mitochondrial electron transport serves as a pathway for this electron transfer.

  • Formation of Water

    • Involves combining electrons with oxygen atoms and hydrogen ions to produce water.

Role of Enzymes

  • Definition and Function

    • Enzymes are biological catalysts that facilitate metabolic processes by lowering the activation energy required.

    • Examples include coenzymes such as NAD and FAD, which accept and transfer electrons during reactions.

Coenzyme Reactions

  • NAD (Nicotinamide Adenine Dinucleotide)

    • Accepts hydrogen atoms (H), resulting in a reduced form, NADH.

  • FAD (Flavin Adenine Dinucleotide)

    • Accepts hydrogen atoms, reducing to FADH, and subsequently forming ATP during transport chain processes.

Glycolysis

  • Overview

    • Glycolysis is the metabolic pathway that converts glucose into pyruvic acid in the cytosol, which does not require oxygen.

    • It breaks one glucose molecule into two pyruvic acid (polarized form) molecules, initiating ATP production.

  • Key Steps

    • Initiation: An enzyme phosphorylates a glucose (creating glucose-6-phosphate).

    • Produces ADP and NADH during the conversion process.

Mitochondrial Functionality

  • Mitochondrial Structure

    • Outer membrane: Permeable to ions and small organic molecules.

    • Inner membrane: Contains proteins for ATP synthesis.

    • Intermembrane space separates the outer and inner membranes.

Citric Acid Cycle (Krebs Cycle)

  • Overview

    • Removes hydrogen atoms from pyruvate, yielding significant energy and releasing CO2.

    • The cycle contributes to GTP (guanosine triphosphate) formation and produces ATP through substrate-level phosphorylation.

  • Energy Production

    • Major source of ATP in cellular metabolism, producing approximately 90% of ATP used by the body.

Electron Transport Chain (ETC)

  • Functionality

    • A series of protein complexes located in the inner mitochondrial membrane.

    • Electrons from NADH and FADH2 are transferred to produce energy.

  • Key Steps of ATP Formation

    • Transfer of electrons through respiratory complexes, generating a proton gradient used for ATP synthesis via chemiosmosis.

Summary of ATP Production

  • ATP Yields

    • From one glucose molecule processed:

    • Glycolysis: 2 ATP

    • NADH from glycolysis: 3 to 5 ATP

    • Citric Acid Cycle: 2 ATP (GTP)

    • Electron Transport Chain: 23 ATP

    • Total Yield: 30 to 32 ATP molecules.

Lipid Metabolism

  • Overview

    • Lipids consist of carbon, hydrogen, and oxygen and are metabolized for energy.

    • Triglycerides split into glycerol and fatty acids, with fatty acids undergoing beta oxidation to enter the citric acid cycle.

  • Beta Oxidation

    • A process that breaks fatty acids down to produce acetyl-CoA, allowing conversion to ATP.

  • Energy Production

    • A single 18-carbon fatty acid can yield up to 120 ATP, exceeding the ATP yield from glucose breakdown.

Protein Metabolism

  • Overview

    • Proteins are made from 20 amino acids, serving various roles such as enzymes and structural components.

    • Amino acids undergo catabolism for energy only after conversion to forms that fit into metabolic pathways.

  • Key Processes

    • Transamination: Transfer of amino groups.

    • Deamination: Removal of amino groups primarily in the liver, producing ammonium ions processed through the urea cycle.

Measuring Metabolic Rate

  • Definition

    • The average rate of caloric expenditure, indicating energy gains and losses.

  • Heat Exchange Mechanisms

    • Methods of heat loss include radiation, convection, conduction, and evaporation, which help maintain homeostasis.

Homeostasis and Thermoregulation

  • Thermoregulatory Mechanisms

    • Body's response to heat via sympathetic nervous system adjustments to regulate blood flow in extremities and maintain optimal temperature.

  • Homeostatic Values

    • Normal body temperature: 37.2°C (99°F).

Gastrointestinal Process

  • Overview

    • The gastrointestinal (GI) tract encompasses the stomach and intestines essential for nutrient processing through ingestion, digestion, absorption, and defecation.

  • Digestive Processes

    • Mechanical Digestion: Physical breakdown by organs.

    • Chemical Digestion: Hydrolytic reactions leading to absorbable materials.

  • Significance of Complete Proteins

    • Foods providing all essential amino acids in ideal proportions support bodily functions without the necessity of excess nitrogen intake.