chapter 6 energy, enzymes, and metabolism

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CHAPTER 6 Energy, Enzymes, and Metabolism. Energy and Energy Conversions. Energy is the capacity to do work Potential energy is the energy of state or position; it includes energy stored in chemical bonds Kinetic energy is the energy of motion - PowerPoint PPT Presentation


  • CHAPTER 6Energy, Enzymes, and Metabolism

  • Energy and Energy ConversionsEnergy is the capacity to do workPotential energy is the energy of state or position; it includes energy stored in chemical bondsKinetic energy is the energy of motionPotential energy can be converted to kinetic energy, which does work.

  • Energy Conversion figure 06-01.jpgKineticPotential

  • First Law of Thermodynamics

    Energy cannot be created or destroyed.

  • Second Law of ThermodynamicsIn a closed system, the quantity of energy available to do work decreases and unusable energy increases Usable energy = free energy (G)Unusable energy = product of entropy (S) and absolute temperature (T) Total energy before transformation = enthalpy (H) figure 06-03.jpg

  • Energy and Energy ConversionsOrganisms are open systems that are part of a larger closed system (universe)

  • Energy and Energy ConversionsChanges in free energy, total energy, temperature, and entropy are related DG = DH TDS

    Exergonic reactionsRelease free energy Have a negative DG Entropy increases, enthalpy decreasesSpontaneousEndergonic reactions Take up free energyHave a positive DG Entropy decreases, enthalpy increasesNon-spontaneous

  • Reactions figure 06-05.jpg

  • Energy and Energy ConversionsG determines equilibrium point Exergonic reactions Equilibrium lies toward completionEndergonic reacitonsReaction will not occur without input of energy G-1-P G-6-P G=-1.7kcal/mol

  • ATP: Transferring Energy in CellsATP - an energy currency in cellsHydrolysis of ATP releases free energy.

  • ATP: Transferring Energy in CellsReaction Coupling couples exergonic and endergonic reactions

  • Coupling Reaction figure 06-10.jpgGlutamate

  • Enzymes: Biological CatalystsRates of reactions are independent of DG Determined by the activation energy Catalysts speed reactions by lowering the activation energy

  • Enzymes: Biological CatalystsHighly specific for their substratesActive sitedetermines specificitywhere catalysis takes placeenzymesubstrate complexDomains

  • Enzymes: Biological CatalystsIn the active site, the substrate is induced into a transition state Transition state temporary substrate configurationInducing & stabilizing the transition state decreases activation energy & increases reaction rate

  • Catalytic Mechanisms figure 06-15.jpgLysozyme

  • Molecular Structure Determines Enzyme FunctionInduced Fit Enzyme conformation alters upon substrate binding

  • Enzymes: Biological CatalystsSubstrate concentration affects the rate of an enzyme-catalyzed reaction

  • Molecular Structure Determines Enzyme FunctionThe active sites of many enzymes contain special reactive molecules which mediate the chemical catalysis

  • Metabolism and Enzyme RegulationMetabolic pathways Upstream downstream sequence of reactions Product of one reaction is a reactant for the next

    Regulation of enzymes Feedback inhibitionDownstream products inhibit upstream enzymes

  • Enzyme Regulation - Competitive InhibitionSuccinate fumarate malate OAABuild up of OAA inhibits succinate dehydrogenase

  • Enzyme Regulation - Competitive InhibitionThr a-Ketobutyrate IleBuildup of Ile inhibits threonine dehydratase

  • Enzyme Regulation - Suicide InhibitorsInhibitor reacts with amino acids in the active site permanently inhibiting the enzymePMSF inhibits serine proteases such as trypsin figure 06-20.jpg

  • Metabolism and Enzyme RegulationAllosteric enzymes, reaction rate v substrate concentration is sigmoidal

  • Enzyme RegulationAllosteric inhibitors bind to sites different from the active site

    Multiple catalytic subunits may interact cooperatively figure 06-23.jpg

  • Enzyme RegulationEnd product of pathway may inhibit upstream allosteric enzymes

  • Enzyme RegulationpH and temperature affect enzyme activity


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