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Chapter 8 An Introduction to Metabolism PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and Jane Reece Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.2 Transformations between kinetic and potential energy On the platform, a diver has more potential energy. Climbing up converts kinetic energy of muscle movement to potential energy. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diving converts potential energy to kinetic energy. In the water, a diver has less potential energy. Figure 8.3 The two laws of thermodynamics Heat + H2O Chemical energy (a) First law of thermodynamics: Energy can be transferred or transformed but neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). co2 (b) Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change • More free energy (higher G) • Less stable • Greater work capacity In a spontaneously change • The free energy of the system decreases (∆G<0) • The system becomes more stable • The released free energy can be harnessed to do work. • Less free energy (lower G) • More stable • Less work capacity (a) Gravitational motion. Objects (b) Diffusion. Molecules move spontaneously from a in a drop of dye diffuse higher altitude to a lower one. until they are randomly dispersed. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (c) Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. Figure 8.6 Free energy changes (G) in exergonic and endergonic reactions Reactants Free energy Amount of energy released (∆G<0) Energy Products Progress of the reaction (a) Exergonic reaction: energy released Free energy Products Amount of energy released (∆G>0) Energy Reactants Progress of the reaction (b) Endergonic reaction: energy required Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.7 Equilibrium and work in closed and open systems ∆G < 0 ∆G = 0 (a) A closed hydroelectric system (b) An open hydroelectric system ∆G < 0 ∆G < 0 ∆G < 0 ∆G < 0 (c) A multistep open hydroelectric system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.8 The structure of adenosine triphosphate (ATP) Adenine N O –O P O– O P O– O P C C N C CH HC O O O N CH2 O O– H Phosphate groups H H Ribose H OH Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NH2 OH N Figure 8.9 The hydrolysis of ATP P P P Adenosine triphosphate (ATP) H2O Pi + Inorganic phosphate P P Adenosine diphosphate (ADP) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Figure 8.10 Energy coupling using ATP hydrolysis Endergonic reaction: ∆G is positive, reaction is not spontaneous NH2 Glu + Glutamic acid NH3 Glu Ammonia Glutamine ∆G = +3.4 kcal/mol Exergonic reaction: ∆ G is negative, reaction is spontaneous ATP + H2O ADP + Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P ∆G = –7.3 kcal/mol ∆G = –3.9 kcal/mol Figure 8.11 How ATP drives cellular work P i P Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP + ATP P Pi P Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins P Glu + NH3 Reactants: Glutamic acid and ammonia NH2 + P i Glu Product (glutamine) made (c) Chemical work: ATP phosphorylates key reactants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings i Figure 8.12 The ATP cycle ATP hydrolysis to ADP + P i yields energy ATP synthesis from ADP + P i requires energy ATP Energy from catabolism (exergonic, energy yielding processes) ADP + P Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings i Energy for cellular work (endergonic, energyconsuming processes) Figure 8.13 Example of an enzyme-catalyzed reaction: hydrolysis of sucrose by sucrase CH2OH CH2OH O O H H H H OH H HO O + HO CH2OH H OH Sucrase H2O OH H CH2OH O H H H OH H OH HO H OH CH2OH O HO H HO H CH2OH OH H Sucrose Glucose Fructose C12H22O11 C6H12O6 C6H12O6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.14 Energy profile of an exergonic reaction The reactants AB and CD must absorb enough energy from the surroundings to reach the unstable transition state, where bonds can break. A B C D Bonds break and new bonds form, releasing energy to the surroundings. Free energy Transition state A B C D EA Reactants A B ∆G < O C D Products Progress of the reaction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.15 The effect of enzymes on reaction rate. Course of reaction without enzyme EA without enzyme Free energy EA with enzyme is lower Reactants ∆G is unaffected by enzyme Course of reaction with enzyme Products Progress of the reaction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.16 Induced fit between an enzyme and its substrate Substrate Active site Enzyme- substrate complex Enzyme (a) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Figure 8.17 The active site and catalytic cycle of an enzyme 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates Enzyme-substrate complex 6 Active site is available for two new substrate molecules. Enzyme 5 Products are Released. Products Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. 3 Active site (and R groups of its amino acids) can lower EA and speed up a reaction by • acting as a template for substrate orientation, • stressing the substrates and stabilizing the transition state, • providing a favorable microenvironment, • participating directly in the catalytic reaction. 4 Substrates are Converted into Products. Figure 8.18 Environmental factors affecting enzyme activity Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction Optimal temperature for typical human enzyme 0 60 40 20 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes Rate of reaction Optimal pH for pepsin (stomach enzyme) 0 1 2 3 4 5 pH Optimal pH for trypsin (intestinal enzyme) 6 OptimalpH for two two enzymes enzymes (b) Optimal pH for Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7 8 9 10 Figure 8.19 Inhibition of enzyme activity A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Competitive inhibitor (b) Competitive inhibition Noncompetitive inhibitor (c) Noncompetitive inhibition Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.20 Allosteric regulation of enzyme activity Allosteric enyzme with four subunits Regulatory site (one of four) Active site (one of four) Allosteric activater stabilizes active from Activator Active form Stabilized active form Oscillation Allosteric activater stabilizes active form NonInactive form Inhibitor functional active site Stabilized inactive form (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Substrate Inactive form Stabilized active form (b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.21 Feedback inhibition in isoleucine synthesis Active site available Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell Intermediate A Feedback inhibition Active site of enzyme 1 no longer binds threonine; pathway is switched off Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 End product (isoleucine) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.22 Organelles and structural order in metabolism Mitochondria, sites of cellular respiration 1 µm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings