Lecture__6_Metabolism_annotated_2

Introduction to Metabolism

  • Metabolism: The acquisition, storage, and use of energy in an organism.

Key Metabolic Components

  • Polysaccharides: Complex carbohydrates like starch and glycogen.

  • Glycoproteins: Molecules consisting of proteins attached to carbohydrates.

  • Lipids: Include fatty acids and membrane compounds.

  • ATP and NADPH: Critical molecules for energy transfer and storage.

Fundamental Tasks of Cells

  1. Synthesize New Parts

    • Components like cell walls, membranes, ribosomes, and nucleic acids.

  2. Harvest Energy

    • Energy fuels cellular reactions, critical for growth and reproduction.

  • The sum of chemical reactions is termed metabolism.

  • Important implications in areas like biofuels and food production, as well as in achieving drug targets.

Energy Types

  • Potential Energy: Stored energy (e.g., chemical bonds).

  • Kinetic Energy: Energy of motion.

Laws of Thermodynamics

  1. First Law: Energy cannot be created or destroyed, only transformed.

  2. Second Law: The universe is naturally inclined toward increased entropy.

Energy Sources in Metabolism

  • Autotrophs: Generate energy from light or inorganic sources.

    • Phototrophs: Use sunlight.

    • Chemotrophs: Use chemical sources.

  • Heterotrophs: Extract energy from organic materials (e.g., animals, plants).

    • Organotrophs: Obtain energy from organic compounds.

    • Lithotrophs: Obtain energy from inorganic compounds.

Microbial Metabolism Factors

  • Temperature: Affects metabolic rate and replication speed.

    • Psychrophiles (cold-loving) to thermophiles (heat-loving) have different growth conditions.

  • Aerotolerance: Organisms differ in their need for oxygen during growth.

    • Types include obligate aerobes, facultative anaerobes, and more.

  • pH Level: Influence on growth; varies across prokaryotes (e.g., acidophiles and alkaliphiles).

  • Water Availability: Affecting organisms’ ability to grow in high-salinity environments.

Metabolic Pathways Overview

  • Anabolism: Building biological molecules; requires energy (endergonic).

  • Catabolism: Breaking down molecules; releases energy (exergonic).

  • Metabolic pathways involve the conversion of substrates into products, regulated by enzymes.

Enzymes and Reaction Control

  • Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

    • Specific to substrates and act in metabolic pathways.

    • Active Site: Enzyme region where substrate binds, inducing a conformation change.

    • Apoenzyme: Inactive enzyme needing a cofactor to function.

Enzyme Inhibition

  1. Noncompetitive Regulation: Inhibitor binds to an allosteric site, altering the enzyme's activity.

  2. Competitive Inhibition: Inhibitor competes with the substrate for the active site.

Metabolic Pathway Characteristics

  • Metabolic Pathway: Chemical reactions converting starting compounds to end products; often involves inhibitors.

  • Phosphorylation: ATP generation mechanisms differ:

    • Substrate-level phosphorylation: Direct ATP generation from exergonic reactions.

    • Oxidative phosphorylation: Involves the electron transport chain (ETC).

Overview of Catabolism

  • Focus on glucose as it is a pivotal energy source and metabolite precursor.

  • Glycolysis: First stage in glucose oxidation; produces ATP and NADH.

    • Divided into two phases: Investment and Payoff.

    • Overall reaction example: Glucose + 2 ATP + 2 ADP + 2 NAD+ → 2 Pyruvate + 4 ATP + 2 NADH.

Pathways after Glycolysis

  • Aerobic Pathway: Requires oxygen to convert pyruvate to CO2 and water.

  • Anaerobic Pathways: Include fermentation with lower energy yields without oxygen.

Krebs Cycle Overview

  • Converts Acetyl CoA to high-energy molecules during oxidative phosphorylation, recycling carbon and generating energy efficiently.

    • Substrates: 2 Acetyl CoA, 6 NAD+, 2 FAD; Products: 4 CO2, 2 GTP (ATP equivalents), 6 NADH, and 2 FADH2.

Electron Transport Chain (ETC)

  • Systems in aerobic respiration consist of large protein complexes that utilize electrons from NADH and FADH2, pumping protons to create a gradient.

  • Significant enzymes in the ETC include:

    • Complex I: Accepts electrons from NADH.

    • Complex II: Accepts from FADH2.

    • Complex III: Transfers electrons to ubiquinone.

    • Complex IV: Transferring electrons to terminal acceptor (O2).

Oxidative Phosphorylation Summary

  • Hydrogen and electrons create a potential gradient leading to ATP synthesis via ATP synthase; a technique critical for energy transfer in cells.