1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and Jane Reece Chapter 8 An Introduction to Metabolism

2. 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. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, a diver has less potential energy.

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.3 The two laws of thermodynamics (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). 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. (b) Chemical energy Heat co 2 H2OH2O +

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change. Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. More free energy (higher G) Less stable Greater work capacity Less free energy (lower G) More stable Less 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 (a) (b) (c)

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.6 Free energy changes (  G) in exergonic and endergonic reactions (a) Exergonic reaction: energy released Reactants Products Energy Progress of the reaction Amount of energy released (∆G<0) Free energy Energy Products Amount of energy released (∆G>0) Progress of the reaction Reactants Free energy (b) Endergonic reaction: energy required

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) A closed hydroelectric system ∆G < 0∆G = 0 (b) An open hydroelectric system ∆G < 0 A multistep open hydroelectric system (c) ∆G < 0 Figure 8.7 Equilibrium and work in closed and open systems

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.8 The structure of adenosine triphosphate (ATP) CH –O–OOOO CH 2 H OH H N HH O N C HC N C C N NH 2 Adenine Ribose O–O– OO O–O– O O–O– P P P Phosphate groups

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.9 The hydrolysis of ATP P Adenosine triphosphate (ATP) H2OH2O + Energy Inorganic phosphate Adenosine diphosphate (ADP) P P PPP i

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.10 Energy coupling using ATP hydrolysis Endergonic reaction: ∆G is positive, reaction is not spontaneous ∆G = +3.4 kcal/mol Glu ∆G = –7.3 kcal/mol ATP H2OH2O + + NH 3 ADP + NH 2 Glutamic acid Ammonia Glutamine Exergonic reaction: ∆ G is negative, reaction is spontaneous P Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.11 How ATP drives cellular work + P Motor protein P i Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ATP Solute P P i ADP + Solute transported (b) Transport work: ATP phosphorylates transport proteins Glu NH 3 NH 2 P i P + (c) Chemical work: ATP phosphorylates key reactants Reactants: Glutamic acid and ammonia Product (glutamine) made

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.12 The ATP cycle ATP synthesis from ADP + P i requires energy ATP ADP + P i Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy yielding processes) ATP hydrolysis to ADP + P i yields energy

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.13 Example of an enzyme-catalyzed reaction: hydrolysis of sucrose by sucrase H2OH2O H H H H HO OH O O O O O H H H H H H H CH 2 OH OH CH 2 OH Sucrase HO OH CH 2 OH H H H O Sucrose Glucose Fructose C 12 H 22 O 11 C 6 H 12 O 6 + H OHH HO

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.14 Energy profile of an exergonic reaction A C D A A B B B C C D D Transition state Products Progress of the reaction ∆G < O Reactants Free energy EAEA The reactants AB and CD must absorb enough energy from the surroundings to reach the unstable transition state, where bonds can break. Bonds break and new bonds form, releasing energy to the surroundings.

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.15 The effect of enzymes on reaction rate. Progress of the reaction Products Course of reaction without enzyme Reactants Course of reaction with enzyme EAEA without enzyme E A with enzyme is lower ∆G is unaffected by enzyme Free energy

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Substrate Active site Enzyme (a) (b) Enzyme- substrate complex Figure 8.16 Induced fit between an enzyme and its substrate

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Products Enzyme Enzyme-substrate complex 5 Products are Released. 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 E A 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. 6 Active site is available for two new substrate molecules.

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.18 Environmental factors affecting enzyme activity Optimal p H for two enzymes Rate of reaction 0 20 40 60 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes (b) Optimal pH for two enzymes pH Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) 1 0 23 4 56 7 8910 (heat-tolerant) bacteria

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.19 Inhibition of enzyme activity 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 (a) Normal binding (b) Competitive inhibition A substrate can bind normally to the active site of an enzyme. A competitive inhibitor mimics the substrate, competing for the active site. Substrate Active site Enzyme Noncompetitive inhibitor (c) Noncompetitive inhibition

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.20 Allosteric regulation of enzyme activity Stabilized inactive form Allosteric activater stabilizes active from Allosteric enyzme with four subunits Active site (one of four) Regulatory site (one of four) Active form Activator Stabilized active form Allosteric activater stabilizes active form Inhibitor Inactive form Non- functional active site (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Oscillation

20. 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.

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.21 Feedback inhibition in isoleucine synthesis Active site available Isoleucine used up by cell Feedback inhibition Isoleucine binds to allosteric site Active site of enzyme 1 no longer binds threonine; pathway is switched off Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine)

22. 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