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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 8: An introduction to Metabolism.

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 8: An introduction to Metabolism."— Presentation transcript:

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2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 8: An introduction to Metabolism

3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Is a living organism an open or closed system? Explain your answer. Start Your Engines

4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism Metabolism in the living cell – Miniature factory where thousands of reactions or energy conversions occur – Energy Free energy Energy in Biological systems ATP – Enzymes Function Regulation

5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Starter. Explain the concept of energy coupling in the of biological system. (hint: think ATP)

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism What is Metabolism – The totality of an organisms chemical reactions.

7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism Metabolism transforms matter and energy, subject to the laws of thermodynamics 1.Energy can be transferred and transformed but NOT destroyed 2. Every energy transformation Increases the entropy in the universe. Energy Conversion is not 100%

8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Pathways Metabolism is Controlled – Metabolism occurs in pathways sometimes with many steps. – Begins w/ specific molecule, ends w/ product – Each step catalyzed by specific enzyme Enzyme 1Enzyme 2Enzyme 3 A B C D Reaction 1Reaction 2Reaction 3 Starting molecule Product

9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism Catabolic pathways – Complex molecules simpler compounds – Release energy Proteins Amino Acids

10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolism Anabolic pathways – Build complicated molecules from simpler ones – Consume energy

11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Energy can be converted from one form to another 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. Figure 8.2 Kinetic Potential Chemical Thermal

12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy in a Biological System Energy conversion Chemical energy

13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Second Law of Thermodynamics Spontaneous changes increase the entropy, or disorder, of the universe Heat co 2 H2OH2O + Energy Conversion is not 100%

14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Living systems – Increase entropy of the universe – Use energy to maintain order 50µm Figure 8.4

15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Free-Energy Change, G Determines if reaction occurs spontaneously

16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Change in free energy, G during a biological process – Related directly to the enthalpy (total energy of a system H) change and the change in entropy G = H – TS Free energy= (Enthalpy) – T(Entropy) Negative G= Spontaneous Positive G = Requires energy

17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exergonic reaction Net release of free E, spontaneous Figure 8.6 Reactants Products Energy Progress of the reaction Amount of energy released (G <0) Free energy (a) Exergonic reaction: energy released

18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endergonic reaction Absorbs free E from surroundings, nonspontaneous Figure 8.6 Energy Products Amount of energy released (G>0) Reactants Progress of the reaction Free energy (b) Endergonic reaction: energy required

19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy in a Biological Systems Maximum stability system at equilibrium 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) Figure 8.5

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic pathways as systems: Closed System Reactions in a closed system eventually reach equilibrium G < 0 G = 0

21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Open System Cells constant flow of materials in and out, do not reach equilibrium G < 0

22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multi-Step Open System Analogy for cellular respiration G < 0 Holy Exergonic Reactions Batman!

23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Cellular Energy Currency (adenosine triphosphate) – Cells Energy shuttle. ATP powers cellular work by coupling exergonic reactions to endergonic reactions Figure 8.8 O O O O CH 2 H OH H N HH O N C HC N C C N NH 2 Adenine Ribose Phosphate groups O O O O O O CH

24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP E released from ATP w hen terminal phosphate bond is broken (hydrolysis) Figure 8.9 P Adenosine triphosphate (ATP) H2OH2O + Energy Inorganic phosphate Adenosine diphosphate (ADP) PP PPP i

25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Must look at total G ATP hydrolysis coupled to other reactions Endergonic reaction: G is positive, reaction is not spontaneous G = +3.4 kcal/mol Glu G = 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

26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular work p owered by hydrolysis of ATP (c) Chemical work : ATP phosphorylates key reactants P Membrane protein Motor protein P i Protein moved (a) Mechanical work : ATP phosphorylates motor proteins ATP (b) Transport work : ATP phosphorylates transport proteins Solute PP i transportedSolute Glu NH 3 NH 2 P i + + Reactants: Glutamic acid and ammonia Product (glutamine) made ADP + P

27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regeneration of ATP Energy from Food!! Catabolic pathways: ATP from ADP and phosphate (ATP Synthesis) 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 Figure 8.12

28 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

29 Enzymes Proteins, speed up metabolic reactions by lowering E barriers Catalyst: speeds up a reaction w/o being consumed by the reaction Proximity

30 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes Substrate – Reactant an enzyme acts on Enzyme – Binds to substrate, forming enzyme-substrate complex Enzyme Complex Substrate

31 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes Lower the E A Barrier Activation energy, E A Initial amount of E needed to start a chemical reaction. Often in the form of heat 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 Figure 8.15 Even w/ -G reaction may be too slow biologically

32 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How Enzymes Work Active site – Region on enzyme where the substrate binds Figure 8.16 Substate Active site Enzyme (a)

33 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Induced fit of substrate – substrate in positions that enhance catalysis Figure 8.16 (b) Enzyme- substrate complex Can be multiple active sites

34 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catalytic cycle of an enzyme Conformational change Substrates Products Enzyme Enzyme-substrate complex 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 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. 5 Products are Released. 1 6 Active site Is available for two new substrate Mole. Figure 8.17

35 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes Enzymes have optimal conditions in which they function Figure 8.18 Optimal temperature for enzyme of thermophilic Rate of reaction Temperature (Cº) (a) Optimal temperature for two enzymes Optimal temperature for typical human enzyme (heat-tolerant) bacteria Temp pH

36 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes Cofactors – Nonprotein enzyme helper Cu +, Mg 2+, Mn 2+ Coenzymes – Organic cofactors NAD, FAD, vitamins

37 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme Regulation Regulation of enzyme activity controls metabolism Cells metabolic pathways tightly regulated

38 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme Regulation: Competitive inhibitors Bind to active site, compete w/ substrate Figure 8.19 (b) Competitive inhibition A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding

39 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme regulation: Noncompetitive inhibitors Bind to another part of enzyme, changing function Figure 8.19 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. Noncompetitive inhibitor (c) Noncompetitive inhibition

40 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme Regulation: Allosteric Proteins function at one site is affected by binding of a regulatory molecule at another site 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 inactivater stabilizes inactive 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 Figure 8.20

41 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme regulation: Cooperativity Cooperativity; allosteric regulation that amplifies enzyme activity Figure 8.20 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.

42 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme Regulation: Feedback Inhibition End product of metabolic pathway shuts down pathway 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) Figure 8.21


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