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Published byΖέφυρ Πύῤῥος Βασιλειάδης Modified over 6 years ago
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CHAPTER 6 Energy, Enzymes, and Metabolism
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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 Potential energy can be converted to kinetic energy, which does work.
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Energy Conversion figure jpg Kinetic Potential
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First Law of Thermodynamics
Energy cannot be created or destroyed.
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Second Law of Thermodynamics
figure jpg In 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)
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Energy and Energy Conversions
Organisms are open systems that are part of a larger closed system (universe)
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Energy and Energy Conversions
Changes in free energy, total energy, temperature, and entropy are related DG = DH – TDS Exergonic reactions Release free energy Have a negative DG Entropy increases, enthalpy decreases Spontaneous Endergonic reactions Take up free energy Have a positive DG Entropy decreases, enthalpy increases Non-spontaneous
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Reactions figure jpg
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Energy and Energy Conversions
G determines equilibrium point Exergonic reactions Equilibrium lies toward completion Endergonic reacitons Reaction will not occur without input of energy G-1-P G-6-P G=-1.7kcal/mol
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ATP: Transferring Energy in Cells
ATP - an energy currency in cells Hydrolysis of ATP releases free energy.
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ATP: Transferring Energy in Cells
Reaction Coupling couples exergonic and endergonic reactions
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Coupling Reaction figure jpg Glutamate
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Enzymes: Biological Catalysts
Rates of reactions are independent of DG Determined by the activation energy Catalysts speed reactions by lowering the activation energy
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Enzymes: Biological Catalysts
Highly specific for their substrates Active site determines specificity where catalysis takes place enzyme–substrate complex Domains
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Enzymes: Biological Catalysts
In the active site, the substrate is induced into a transition state Transition state temporary substrate configuration Inducing & stabilizing the transition state decreases activation energy & increases reaction rate
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Catalytic Mechanisms figure jpg Lysozyme
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Molecular Structure Determines Enzyme Function
Induced Fit Enzyme conformation alters upon substrate binding
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Enzymes: Biological Catalysts
Substrate concentration affects the rate of an enzyme-catalyzed reaction
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Molecular Structure Determines Enzyme Function
The active sites of many enzymes contain special reactive molecules which mediate the chemical catalysis
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Metabolism and Enzyme Regulation
Metabolic pathways Upstream downstream sequence of reactions Product of one reaction is a reactant for the next Regulation of enzymes Feedback inhibition Downstream products inhibit upstream enzymes
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Enzyme Regulation - Competitive Inhibition
Succinate fumarate malate OAA Build up of OAA inhibits succinate dehydrogenase
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Enzyme Regulation - Competitive Inhibition
Thr a-Ketobutyrate Ile Buildup of Ile inhibits threonine dehydratase
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Enzyme Regulation - Suicide Inhibitors
figure jpg Inhibitor reacts with amino acids in the active site permanently inhibiting the enzyme PMSF inhibits serine proteases such as trypsin
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Metabolism and Enzyme Regulation
Allosteric enzymes, reaction rate v substrate concentration is sigmoidal
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Enzyme Regulation figure jpg Allosteric inhibitors bind to sites different from the active site Multiple catalytic subunits may interact cooperatively
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Enzyme Regulation End product of pathway may inhibit upstream allosteric enzymes
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Enzyme Regulation pH and temperature affect enzyme activity
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