Metabolism - Electron Flow and Energy Production (1)

Metabolism Overview

  • Electron Flow and Energy Production

    • Metabolism encompasses all biochemical reactions, primarily involving electron flow for energy production.

Energy Metabolism Processes

  • Anabolism vs. Catabolism

    • Anabolism: Uses nutrients for biosynthesis, requires energy to form macromolecules and cellular components.

    • Catabolism: Breaks down organic and inorganic compounds to release energy, used for motility and nutrient transport.

    • Waste products from catabolism include fermentation by-products (acids, alcohols, gases).

Understanding Metabolism

  • Definition of Metabolism

    • Sum of all chemical reactions in a cell.

    • Catabolic reactions: Energy-producing processes, breaking down molecules.

    • Anabolic reactions: Energy-using processes, building complex molecules.

Redox Reactions in Energy Production

  • Oxidation-Reduction Reactions

    • Oxidation: Loss of electrons.

    • Reduction: Gain of electrons.

    • These reactions are coupled; electron donors transfer electrons to acceptors, where donors get oxidized and acceptors are reduced.

Example of a Redox Reaction

  • Overall Reaction:

    • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

    • Glucose (C6H12O6) oxidized to CO2; O2 reduced to H2O.

Electron Carriers in Metabolism

  • Role of Electron Carriers: Facilitate electron transfer from donors to acceptors.

    • Includes membrane-bound carriers (e.g., cytochrome c) and freely diffusible coenzymes (e.g., NAD+/NADH).

    • NAD+/NADH details:

      • NAD+: Oxidized form

      • NADH: Reduced form, involved in electron transport and energy production.

Enzymatic Reactions and Energy Transfer

  • Enzyme Reactions:

    • Reaction 1: Enzyme I + NAD+ reacts with substrate to form NADH, produce CO2, and generate a-ketoglutarate.

    • Reaction 2: Enzyme II + NADH reacts with a-ketoglutarate to form Glutamate.

NAD+/NADH Cycling - Key Steps

  1. Enzyme I reacts with electron donor and NAD+ to form NADH.

  2. The product is released.

  3. Enzyme II then reacts with the electron acceptor and NADH, regenerating NAD+.

Energy Currency in Cells

  • ATP (Adenosine Triphosphate):

    • Main energy carrier in biological systems.

    • Contains two high-energy phosphoanhydride bonds.

  • Energy Storage Compounds:

    • Short-term: ATP.

    • Long-term: Glycogen, Poly-β-hydroxybutyrate, elemental sulfur.

Phosphorylation Processes

  • Substrate-level Phosphorylation: Direct transfer of phosphate from a substrate to ADP to synthesize ATP.

  • Oxidative Phosphorylation: Inorganic phosphate is added to ADP via ATP synthase, utilizing the proton motive force.

Common Enzymes in Metabolism

  • Dehydrogenases: Involved in oxidation reactions. E.g., Glyceraldehyde-3-P dehydrogenase (glycolysis), Lactate dehydrogenase (fermentation).

  • Kinases: Phosphorylate substrates. E.g., Hexokinase (first step of glycolysis).

  • Synthases: Catalyze synthesis reactions. E.g., ATP synthase (oxidative phosphorylation).

Glycolysis Overview

  • Role in Metabolism: Major pathway of glucose metabolism.

  • Outputs: Produces 2 ATP and 2 pyruvate per glucose, occurring in the cytoplasm of cells.

  • Key Steps: Include substrate-level phosphorylation at steps 7 and 10, involving ATP formation.

Fermentation vs. Respiration

  • Anaerobic Processes:

    • Fermentation: Occurs without electron acceptor; yields few ATP.

    • Respiration: Uses electron acceptors (O2 or other molecules) to completely oxidize substrates, producing more ATP.

Types of Fermentation**

  • Alcohol Fermentation: Produces ethanol and CO2 from glucose. Key organisms include yeast.

  • Lactate Fermentation: Produces lactic acid from glucose, involves microbes like Streptococcus.

Methanogenesis and Acetogenesis**

  • Methanogenesis: Anaerobic production of methane by methanogenic archaea from CO2 and H2, crucial in various ecosystems and bioreactors.

  • Acetogenesis: Involves production of acetate from CO2 and H2, important in certain anaerobic bacteria.

Calvin-Benson Cycle**

  • Component of Photosynthesis: Uses ATP to fix CO2 into organic compounds. Key reactions involve enzyme RubisCO and energy input for biosynthesis.

Phototrophic Organisms**

  • Photoautotrophs vs. Photoheterotrophs: Different types of organisms using light as an energy source.

  • Photoautotrophs utilize CO2, whereas photoheterotrophs utilize organic compounds.

Summary of Key Differences**

  • Fermentation: Primarily substrate-level phosphorylation, no electron transport system.

  • Respiration: Involves electron transport, generates more ATP through substrate-level and oxidative phosphorylation.