Chapter 6: Energy, Enzymes, and Metabolism CHAPTER 6 Energy, Enzymes, and Metabolism

Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Energy and Energy Conversions ATP: Transferring Energy in Cells ATP: Transferring Energy in Cells Enzymes: Biological Catalysts Enzymes: Biological Catalysts

Chapter 6: Energy, Enzymes, and Metabolism Molecular Structure Determines Enzyme Function Molecular Structure Determines Enzyme Function Metabolism and the Regulation of Enzymes Metabolism and the Regulation of Enzymes

Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Energy is the capacity to do work.Energy is the capacity to do work. Potential energy is the energy of state or position; it includes energy stored in chemical bonds.Potential energy is the energy of state or position; it includes energy stored in chemical bonds. Kinetic energy is the energy of motion.Kinetic energy is the energy of motion.4

Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Potential energy can be converted to kinetic energy, which does work. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions The first law of thermodynamics tells us energy cannot be created or destroyed. The second tells us that, in a closed system, the quantity of energy available to do work decreases and unusable energy increases. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Living things obey the laws of thermodynamics. Organisms are open systems that are part of a larger closed system. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Changes in free energy, total energy, temperature, and entropy are related by the equation  G =  H – T  S.Changes in free energy, total energy, temperature, and entropy are related by the equation  G =  H – T  S.11

Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions Spontaneous, exergonic reactions release free energy and have a negative  G. Non-spontaneous, endergonic reactions take up free energy, have a positive  G, and proceed only if free energy is provided. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions The change in free energy of a reaction determines its point of chemical equilibrium, at which forward and reverse reactions proceed at the same rate. For spontaneous, exergonic reactions, the equilibrium point lies toward completion. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism ATP: Transferring Energy in Cells ATP serves as an energy currency in cells.ATP serves as an energy currency in cells. Hydrolysis of ATP releases a relatively large amount of free energy.Hydrolysis of ATP releases a relatively large amount of free energy. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism ATP: Transferring Energy in Cells The ATP cycle couples exergonic and endergonic reactions, transferring free energy from the exergonic to the endergonic reaction. Review Figures 6.9,

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Chapter 6: Energy, Enzymes, and Metabolism Enzymes: Biological Catalysts The rate of a chemical reaction is independent of  G but is determined by the size of the activation energy barrier.The rate of a chemical reaction is independent of  G but is determined by the size of the activation energy barrier. Catalysts speed reactions by lowering the barrier.Catalysts speed reactions by lowering the barrier. Review Figures 6.11,

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Chapter 6: Energy, Enzymes, and Metabolism Enzymes: Biological Catalysts Enzymes are biological catalysts, highly specific for their substrates. Substrates bind to the active site, where catalysis takes place, forming an enzyme– substrate complex. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Enzymes: Biological Catalysts At the active site, a substrate can be oriented correctly, chemically modified, or strained.At the active site, a substrate can be oriented correctly, chemically modified, or strained. As a result, the substrate readily forms its transition state, and the reaction proceeds.As a result, the substrate readily forms its transition state, and the reaction proceeds. Review Figures 6.14,

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Chapter 6: Energy, Enzymes, and Metabolism Enzymes: Biological Catalysts Substrate concentration affects the rate of an enzyme-catalyzed reaction. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Molecular Structure Determines Enzyme Function The active site where substrate binds determines the specificity of an enzyme.The active site where substrate binds determines the specificity of an enzyme. Upon binding to substrate, some enzymes change shape, facilitating catalysis.Upon binding to substrate, some enzymes change shape, facilitating catalysis. Review Figures 6.13,

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Chapter 6: Energy, Enzymes, and Metabolism Molecular Structure Determines Enzyme Function Some enzymes require cofactors for catalysis. Prosthetic groups are permanently bound to the enzyme. Coenzymes usually are not. They enter into the reaction as a “cosubstrate,” as they are changed by the reaction and released from the enzyme. Review Table

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Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes Metabolism is organized into pathways: the product of one reaction is a reactant for the next.Metabolism is organized into pathways: the product of one reaction is a reactant for the next. Each reaction is catalyzed by an enzyme.Each reaction is catalyzed by an enzyme.35

Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes Enzyme activity is subject to regulation. Some compounds react irreversibly with them and reduce their catalytic activity. Others react reversibly, inhibiting enzyme action temporarily. A compound structurally similar to an enzyme’s normal substrate may inhibit enzyme action. Review Figures 6.20,

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Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes For allosteric enzymes, plots of reaction rate versus substrate concentration are sigmoidal, in contrast to plots of the same variables for non-allosteric enzymes. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes Allosteric inhibitors bind to a site different from the active site and stabilize the inactive form of the enzyme.Allosteric inhibitors bind to a site different from the active site and stabilize the inactive form of the enzyme. The multiple catalytic subunits of many allosteric enzymes interact cooperatively.The multiple catalytic subunits of many allosteric enzymes interact cooperatively. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes The end product of a metabolic pathway may inhibit the allosteric enzyme that catalyzes the commitment step of the pathway. Review Figure

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Chapter 6: Energy, Enzymes, and Metabolism Metabolism and the Regulation of Enzymes Enzymes are sensitive to their environment. Both pH and temperature affect enzyme activity. Review Figures 6.25,

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