Electron Transport Chain

Invasive Species in Michigan

  • Aquatic Invasive Species (AIS): Priority species identified as significant threats to Michigan's natural resources.

    • Importance: Early detection and timely reporting crucial for prevention.

    • Watch List Species:

      • Grass Carp (Ctenopharyngodon idella)

      • Snakehead (Channa argus)

      • New Zealand Mudsnail (Potamopyrgus jenkinsi)

      • Red Swamp Crayfish (Procambarus clarkii)

      • Bighead Carp (Hypophthalmichthys nobilis)

      • Black Carp (Mylopharyngodon piceus)

Biochemistry of the Electron Transport Chain (ETC)

Understanding the Basics

  • Mitochondrion Structure:

    • Two membranes: Outer (permeable to small molecules) and Inner (impermeable, requires transporters).

  • Mitochondrial Cristae:

    • Convolutions of the inner membrane; more present in cells with high metabolic activity.

Focus Questions

  • Basic structure of mitochondria.

  • ATP and ADP transport mechanisms.

  • Glycerol 3-phosphate and malate-aspartate shuttles and their purposes.

  • Role of electron transport in ATP synthesis via redox potential and proton motive force.

  • Experimental procedures to determine electron transfer order in the ETC.

  • Path of electrons from NADH and FADH2 entering the ETC.

  • Mitochondria's mechanisms to prevent ROS release.

  • Calculation of ATP production in various scenarios.

Mitochondrial Electron Transport & ATP-ADP Translocase

  • ATP-ADP Transport: Mechanism of translocase responsible for moving ADP into the mitochondria while exporting ATP.

Shuttles for Electron Transport

  1. Glycerol 3-phosphate Shuttle:

    • Utilizes NADH from the cytosol to reduce dihydroxyacetone phosphate (DHAP) to glycerol 3-phosphate, which is oxidized to reform DHAP while producing FADH2.

    • Predominantly found in skeletal muscles.

  2. Malate-Aspartate Shuttle:

    • Transfers electrons from cytosolic NADH to mitochondrial matrix using oxaloacetate and glutamate.

    • Predominantly active in heart and liver tissues.

  • Return Mechanism: Transports oxaloacetate back to cytosol while generating alpha-ketoglutarate.

Components of the Electron Transport Chain

  • Electron Movement:

    • Electrons flow down an energy gradient, creating a proton gradient.

    • Complex I: Transfers electrons from NADH to Ubiquinone, pumping protons out of the matrix.

    • Complex II: Succinate to Ubiquinone, no proton pumping involved.

    • Complex III: Transfers electrons from Ubiquinone to cytochrome c, pumps protons into the intermembrane space.

    • Complex IV: Carries electrons to molecular oxygen, reducing it to water and pumping protons across the membrane.

Proteins as Electron Carriers

  • Coenzyme Q: Transfers protons and electrons, exists in various oxidation states.

  • Cytochromes: Electron transfer proteins containing heme groups that facilitate single electron transfers.

  • Iron-Sulfur Proteins: Participate in one-electron transfers, important for various biological oxidation-reduction reactions.

Energy and Proton-Motive Force

  • Proton-motive force: Energy stored in the electrochemical gradient across the mitochondrial inner membrane, composed of both chemical and electrical potential energy.

Quick Quizzes

  • Quiz 1: True/False statements about electron transfer processes.

    1. Iron-sulfur clusters can transfer two electrons at a time.

    2. Molecular oxygen is a strong oxidizing agent.

    3. Protons are pumped from matrix to intermembrane space.

  • Quiz 2: Identify the true statement in a set about the ETC and electron transfers.

Reactive Oxygen Species (ROS)

  • Production of ROS from partial O2 reduction poses risks, linked to various pathological conditions.

  • Protective Mechanisms:

    • Enzymes like superoxide dismutase (SOD) convert superoxide radicals into hydrogen peroxide, which catalase then decomposes into water and oxygen.

ATP Calculation from Glucose Oxidation

  • 1 mole NADH produces 2.5 moles ATP; 1 mole FADH2 produces 1.5 moles ATP. Total ATP from complete glucose oxidation must be calculated based on glycolysis, PDC, and CAC pathways.

Summary: Citric Acid Cycle and Its Role in Cancer

  • Introduction: Discussion on the citric acid cycle (CAC), its metabolic significance, and its connection to cancer.

  • Focus Questions: Review relationships between glycolysis and CAC, and understand different nomenclatures like CAC (Citric Acid Cycle), TCA (Tricarboxylic Acid Cycle), and Kreb Cycle.

  • Glycolysis to CAC Connection: Pyruvate from glycolysis can convert to acetyl CoA, which feeds into the CAC, ultimately producing CO2 and reducing equivalents.

  • Overview of CAC: The CAC begins with the condensation of oxaloacetate and acetyl CoA, undergoing oxidative decarboxylation to produce reducing equivalents, eventually regenerating oxaloacetate.

  • Amphibolic Pathway: CAC serves both anabolic and catabolic functions. Intermediates can be used for amino acid synthesis and other metabolic processes. Anaplerotic reactions replenish CAC intermediates.

  • Reaction Steps: Detailed examination of individual steps, enzymes involved (like citrate synthase, aconitase), and regulatory mechanisms influenced by energy charge (ATP, NADH levels).

  • Regulation of CAC: The activity varies based on cellular energy states—high ATP/NADH favors storage processes while low levels stimulate CAC activity.

  • CAC and Cancer: Defects in CAC enzymes can lead to altered metabolic pathways that promote cancer progression through mechanisms like hypoxia-inducible factor activation, facilitating blood vessel growth, and changing DNA methylation patterns, significantly impacting gene expression.