1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick An Introduction to Metabolism Chapter 8

2. Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics Metabolism –Catabolism: “energy releasing” –Anabolism: “energy consuming” © 2011 Pearson Education, Inc.

3. Figure 8.3a (a)First law of thermodynamics = conservation of energy Chemical energy

4. Figure 8.3b (b) Second law of thermodynamics = law of entropy Heat

5. Free-Energy Change,  G Energy that can do work © 2011 Pearson Education, Inc.

6. The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T) ∆G = ∆H – T∆S Only processes with a negative ∆G are spontaneous Spontaneous processes can be harnessed to perform work © 2011 Pearson Education, Inc.

7. Figure 8.5 More free energy (higher G) Less stable Greater work capacity In a spontaneous 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 (b) Diffusion(c) Chemical reaction

8. Exergonic and Endergonic Reactions in Metabolism exergonic reaction: net release of free energy and is spontaneous endergonic reaction: absorbs free energy from its surroundings and is nonspontaneous © 2011 Pearson Education, Inc.

9. Figure 8.6 (a) Exergonic reaction: energy released, spontaneous (b) Endergonic reaction: energy required, nonspontaneous Reactants Energy Products Progress of the reaction Amount of energy released (  G  0) Reactants Energy Products Amount of energy required (  G  0) Progress of the reaction Free energy

10. Equilibrium and Metabolism Reactions in a closed system eventually reach equilibrium and then do no work Cells are not in equilibrium; they are open systems experiencing a constant flow of materials A defining feature of life is that metabolism is never at equilibrium © 2011 Pearson Education, Inc.

11. Figure 8.7c (c) A multistep open hydroelectric system  G  0

12. Figure 8.8 (a) The structure of ATP Phosphate groups Adenine Ribose Adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP

13. Figure 8.9 Glutamic acid Ammonia Glutamine (b) Conversion reaction coupled with ATP hydrolysis Glutamic acid conversion to glutamine (a) (c) Free-energy change for coupled reaction Glutamic acid Glutamine Phosphorylated intermediate Glu NH 3 NH 2 Glu  G Glu = +3.4 kcal/mol ATP ADP NH 3 Glu P P i ADP Glu NH 2  G Glu = +3.4 kcal/mol Glu NH 3 NH 2 ATP  G ATP =  7.3 kcal/mol  G Glu = +3.4 kcal/mol +  G ATP =  7.3 kcal/mol Net  G =  3.9 kcal/mol 1 2

14. Figure 8.10 Transport protein Solute ATP P P i ADP P i ADP ATP Solute transported Vesicle Cytoskeletal track Motor proteinProtein and vesicle moved (b) Mechanical work: ATP binds noncovalently to motor proteins and then is hydrolyzed. (a) Transport work: ATP phosphorylates transport proteins.

15. Figure 8.11 Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP ADPP i H2OH2O

16. Figure 8.UN02 Sucrase Sucrose (C 12 H 22 O 11 ) Glucose (C 6 H 12 O 6 ) Fructose (C 6 H 12 O 6 )

17. Figure 8.12 Transition state Reactants Products Progress of the reaction Free energy EAEA  G  O A B C D A B C D A B C D

18. Figure 8.13 Course of reaction without enzyme E A without enzyme E A with enzyme is lower Course of reaction with enzyme Reactants Products  G is unaffected by enzyme Progress of the reaction Free energy

19. Substrate Specificity of Enzymes substrate enzyme-substrate complex active site Induced fit © 2011 Pearson Education, Inc.

20. Figure 8.14 Substrate Active site Enzyme Enzyme-substrate complex (a) (b)

21. Catalysis in the Enzyme’s Active Site In an enzymatic reaction, the substrate binds to the active site of the enzyme The active site can lower an E A barrier by –Orienting substrates correctly –Straining substrate bonds –Providing a favorable microenvironment –Covalently bonding to the substrate © 2011 Pearson Education, Inc.

22. Figure 8.15-1 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. 1 2 Enzyme Active site

23. Figure 8.15-2 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. Active site can lower E A and speed up a reaction. 1 2 3 Substrates are converted to products. 4 Enzyme Active site

24. Figure 8.15-3 Substrates Substrates enter active site. Enzyme-substrate complex Enzyme Products Substrates are held in active site by weak interactions. Active site can lower E A and speed up a reaction. Active site is available for two new substrate molecules. Products are released. Substrates are converted to products. 1 2 3 4 5 6

25. Figure 8.16 Optimal temperature for typical human enzyme (37°C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C) Temperature (°C) (a) Optimal temperature for two enzymes Rate of reaction 120 100 80 60 40200 0 12 3 4 5 6 78910 pH (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme)

26. Cofactors organic cofactor = coenzyme –vitamins © 2011 Pearson Education, Inc.

27. Enzyme Inhibitors Competitive inhibitors Noncompetitive inhibitors Examples of inhibitors include toxins, poisons, pesticides, and antibiotics © 2011 Pearson Education, Inc.

28. Figure 8.17 (a) Normal binding(b) Competitive inhibition (c) Noncompetitive inhibition Substrate Active site Enzyme Competitive inhibitor Noncompetitive inhibitor

29. The Evolution of Enzymes Enzymes = proteins encoded by genes Changes (mutations) in genes lead to changes in amino acid composition of an enzyme Altered amino acids in enzymes may alter their substrate specificity Under new environmental conditions a novel form of an enzyme might be favored © 2011 Pearson Education, Inc.

30. Figure 8.19 Regulatory site (one of four) (a) Allosteric activators and inhibitors Allosteric enzyme with four subunits Active site (one of four) Active form Activator Stabilized active form Oscillation Non- functional active site Inactive form Inhibitor Stabilized inactive form Inactive form Substrate Stabilized active form (b) Cooperativity: another type of allosteric activation

31. Allosteric Activation and Inhibition Most allosterically regulated enzymes are made from polypeptide subunits Each enzyme has active and inactive forms The binding of an activator stabilizes the active form of the enzyme The binding of an inhibitor stabilizes the inactive form of the enzyme © 2011 Pearson Education, Inc.

32. Cooperativity is a form of allosteric regulation that can amplify enzyme activity One substrate molecule primes an enzyme to act on additional substrate molecules more readily Cooperativity is allosteric because binding by a substrate to one active site affects catalysis in a different active site © 2011 Pearson Education, Inc.

33. Identification of Allosteric Regulators Allosteric regulators are attractive drug candidates for enzyme regulation because of their specificity Inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses © 2011 Pearson Education, Inc.

34. Figure 8.20 Caspase 1 Active site Substrate SH Known active form Active form can bind substrate Allosteric binding site Allosteric inhibitor Hypothesis: allosteric inhibitor locks enzyme in inactive form Caspase 1 Active formAllosterically inhibited form Inhibitor Inactive form EXPERIMENT RESULTS Known inactive form

35. Feedback Inhibition In feedback inhibition, the end product of a metabolic pathway shuts down the pathway Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed © 2011 Pearson Education, Inc.

36. Figure 8.21 Active site available Isoleucine used up by cell Feedback inhibition Active site of enzyme 1 is no longer able to catalyze the conversion of threonine to intermediate A; pathway is switched off. Isoleucine binds to allosteric site. 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)