Microbio 310 1st Edition Lecture 7Outline of Last Lecture I. 3.1 Cell MorphologyII. 3.2 Cell Size and the Significance of SmallnessIII. 3.3 The Cytoplasmic MembraneIV. 3.4 Functions of the Cytoplasmic MembraneV. 3.6 The Cell Wall of Bacteria: PeptidoglycanVI. 3.7 The Outer MembraneVII. 3.8 Cell Walls of ArchaeaVIII. 3.9 Cell Surface StructuresIX. 3.10 Cell InclusionsX. 3.11 Gas VesiclesXI. 3.12 EndosporesXII. 3.13 Flagella and MotilityXIII. 3.15 Microbial TaxesOutline of Current Lecture I. 4.6 Electron Donors and Electron AcceptorsII. 4.7 Energy-Rich Compounds and Energy StorageIII. 4.8 Glycolysis IV. 4.9 Respiration and Electron Carriers These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.V. 4.10 The Proton Motive Force VI. 4.11 The Citric Acid Cycle VII. 4.12 Catabolic Diversity VIII. 4.14 Biosynthesis of Amino Acids and NucleotidesIX. 4.15 Biosynthesis of Fatty Acids and LipidsCurrent Lecture4.6 Electron Donors and Electron Acceptors- Energy from oxidation–reduction (redox) reactions is used in synthesis of energy-rich compounds (e.g., ATP)- Redox reactions occur in pairs (two half reactions) - Electron donor: the substance oxidized in a redox reaction - Electron acceptor: the substance reduced in a redox reaction - Useful acronym: OIL RIG (Oxidation Is Loss and Reduction Is Gain)- Reduction potential (E0′ ) : tendency to donate electrons – Expressed as volts (V) - Substances can be either electron donors or acceptors under different circumstances (redox couple)- Reduced substance of a redox couple with a more negative E0 donates electrons to the ′oxidized substance of a redox couple with a more positive E0 ′- The redox towerrepresents the range of possible reduction potentials. The reduced substance at the top of the tower donates electrons.- The farther the electrons “drop,Cthe greater the amount of energy released – Passing of electrons leads to free energy that is captured- Redox reactions usually involve reactions between intermediates (carriers) - Electron carriers are divided into two classes:– Prosthetic groups (attached to enzymes) – Coenzymes (diffusible) - Examples: NAD+, NADP - NAD+ and NADH facilitate redox reactions without being consumed; they are recycled 4.7 Energy-Rich Compounds and Energy Storage- Chemical energy released in redox reactions is primarily stored in certain phosphorylated compounds– ATP; the prime energy currency - Portable energy source; can capture energy in one place and use itsomewhere else– Phosphoenolpyruvate– Glucose 6-phosphate- Chemical energy also stored in coenzyme A• Long-term energy storage involves insoluble polymers that can be oxidized to generate ATP– Examples in prokaryotes• Glycogen• Poly--hydroxybutyrate (acetylCoA polymer ‘bioplastic’)• Elemental sulfur– Examples in eukaryotes• Starch• Lipids (simple fats)-we do store energy in fat4.8 Glycolysis• Two reaction series are linked to energy conservation in chemoorganotrophs: fermentation and respiration • Differ in mechanism of ATP synthesis– Fermentation: substrate-level phosphorylation; ATP directly synthesized from an energy-rich intermediate; lactate is a product– Respiration: oxidative phosphorylation; ATP produced from proton motive force formed by transport of electrons• Fermented substance is both an electron donor and an electron acceptor• Glycolysis:a common pathway for catabolism of glucose– Anaerobic process (no oxygen)– Gluco –lysed– 2 ATP from SLP– Alcohol4.9 Respiration and Electron Carriers• AerobicRespiration– Oxidation using O2 as the terminal electron acceptor– Higher ATP yield than fermentation• ATP produced at the expense of the proton motive force, which is generated by electron transport• Electron Transport Systems– Membrane associated (inner membrane of mitochondria)– Mediate transfer of electrons– Conserve some of the energy released during transfer and use it to synthesizeATP– Many oxidation–reduction enzymes are involved in electron transport (e.g., NADH dehydrogenases, flavoproteins, iron– sulfur proteins, cytochromes)- NADH dehydrogenases: proteins bound to inside surface of cytoplasmic membrane; active site binds NADH and accepts 2 electrons and 2 protons that are passed to flavoproteins- Flavoproteins: contains flavin prosthetic group (e.g., FMN, FAD) that accepts 2 electrons and 2 protons but only donates the electrons to the next protein in the chain • Cytochromes– Proteins that contain heme prosthetic groups– Accept and donate a single electron via the iron atom in heme4.10 The Proton Motive Force- Electron transport system oriented in cytoplasmic membrane so that electrons are separated from protons- Electron carriers arranged in membrane in order of their reduction potential– Carrier with most reducing potential is farthest down the line- The final carrier in the chain donates the electrons and protons to the terminal electron acceptor- During electron transfer, several protons (H+) are released on the outside of the membrane– Protons originate from NADH and the dissociation of water- Results in generation of pH gradient and an electrochemical potential across the membrane (the proton motive force)– The inside becomes electrically negative and alkaline (lower concentration of H+)– The outside becomes electrically positive and acidic (higher concentration of H+)- Complex I (NADH:quinoneoxidoreductase) – NADH donates e-to FAD– FADH donates e-to quinone- Complex II (succinate dehydrogenase complex) – Bypasses Complex I – Feeds e-and H+from FADH directly to quinone pool • Complex III (cytochrome bc1 complex)– Transfers e from quinones to cytochrome c– Cytochrome c shuttles e to cytochromes a and a3• Complex IV (cytochromes a and a3)– Terminal oxidase; reduces O2 to H2O• ATP synthase (ATPase) : complex that converts proton motive force into ATP; enzyme that makes ATP; two components– F1: multiproteinextramembrane complex, faces cytoplasm, responsible for catalyzing the formation of ATP– Fo: proton-conducting intramembrane channel, flow of protons through this channel causes it to rotate– Uses mechanical/rotational and potential energyo Mechanical force allows ADP and P to be pushed together– Reversible (can run in both directions: make ATP or make ADP); dissipates proton motive