Biology Sylvia S. Mader Michael Windelspecht Chapter 6 Metabolism: Energy and Enzymes Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1

Outline 6.1 Cells and the Flow of Energy 6.2 Metabolic Reactions and Energy Transformations 6.3 Metabolic Pathways and Enzymes 6.4 Organelles and the Flow of Energy 2

6.1 Cells and the Flow of Energy Energy – The ability to do work or bring about a change  Kinetic energy Energy of motion Mechanical  Potential energy Stored energy Chemical energy 3

Flow of Energy 4 solar energy heat Mechanical energy Chemical energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Two Laws of Thermodynamics First law:  Law of conservation of energy  Energy cannot be created or destroyed, but can be changed from one form to another Second law:  Law of entropy  When energy is changed from one form to another, there is a loss of usable energy  Waste energy goes to increase disorder 5

6 Entropy  S  S

sun CO 2 H2OH2O solar energyproducer carbohydrate heat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Carbohydrate Metabolism 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carbohydrateuncontracted musclecontracted muscle heat

Cells and Entropy 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H2OH2O C 6 H 12 O 6 more organized more potential energy less stable (entropy) a. Carbon dioxide and water less organized less potential energy more stable (entropy) CO 2 kinetic energy channel protein H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Unequal distribution of hydrogen ions Equal distribution of hydrogen ions more organized more potential energy b. less stable (entropy) less organized less potential energy more stable (entropy) Glucose H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

6.2 Metabolic Reactions and Energy Transformations Metabolism  Sum of cellular chemical reactions in cell  Reactants participate in a reaction  Products form as result of a reaction Free energy is the amount of energy available to perform work  Exergonic Reactions - Products have less free energy than reactants (release energy)  Endergonic Reactions - Products have more free energy than reactants (require energy input) 10

11 ATP and Coupled Reactions Adenosine triphosphate (ATP)  High energy compound used to drive metabolic reactions  Constantly being generated from adenosine diphosphate (ADP) Composed of:  Adenine and ribose (together = adenosine), and  Three phosphate groups Coupled reactions  Energy released by an exergonic reaction captured in ATP  That ATP used to drive an endergonic reaction

The ATP Cycle 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PPP adenosine triphosphate ATP is unstable and has a high potential energy. ATP

The ATP Cycle 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PP P P adenosine triphosphate ATP is unstable and has a high potential energy. ATP Exergonic Reaction: The hydrolysis of ATP releases previously stored energy, allowing the change in free energy to do work and drive other processes. Has negative delta G. Examples: protein synthesis, nerve conduction, muscle contraction ATP +

The ATP Cycle 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PP + P PPP + P adenosine triphosphate ATP is unstable and has a high potential energy. ATP Exergonic Reaction: The hydrolysis of ATP releases Previously stored energy, allowing the change in free energy to do work and drive other processes. Has negative delta G. Examples: protein synthesis, nerve conduction, muscle contraction adenosine diphosphatephosphate ADP is more stable and has lower potential energy than ATP. + ADP

The ATP Cycle 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PP + P PPP + + P Endergonic Reaction: Creation of ATP from ADP and Prequires input of energy from Other sources. Has positive delta G. Example: cellular respiration adenosine triphosphate ATP is unstable and has a high potential energy. ATP ADP adenosine diphosphatephosphate ADP is more stable and has lower potential energy than ATP. Exergonic Reaction: The hydrolysis of ATP releases Previously stored energy, allowing the change in free energy to do work and drive other processes. Has negative delta G. Examples: protein synthesis, nerve conduction, muscle contraction

Coupled Reactions 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Myosin assumes its resting shape when It combines with ATP. myosin actin ATP

Coupled Reactions 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 2 P Myosin assumes its resting shape when It combines with ATP. ATP splits into ADP and p, causing myosin to change its shape and allowing it to attach to actin. ADP myosin actin ATP

Coupled Reactions 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display P Myosin assumes its resting shape when It combines with ATP. ATP splits into ADP and p, causing myosin to change its shape and allowing it to attach to actin. Release of ADP and p cause myosin to again change shape and pull again stactin, generating force and motion. ADP myosin actin ATP

Coupled Reactions 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display P Myosin assumes its resting shape when It combines with ATP. ATP splits into ADP and p, causing myosin to change its shape and allowing it to attach to actin. Release of ADP and p cause myosin to again change shape and pull against actin, generating force and motion. ADP myosin actin ATP

Work-Related Functions of ATP Primarily to perform cellular work  Chemical Work - Energy needed to synthesize macromolecules  Transport Work - Energy needed to pump substances across plasma membrane  Mechanical Work - Energy needed to contract muscles, beat flagella, etc 20

21 Metabolic Pathways Reactions are usually occur in a sequence  Products of an earlier reaction become reactants of a later reaction  Such linked reactions form a metabolic pathway Begins with a particular reactant, Proceeds through several intermediates, and Terminates with a particular end product AG A  B  C  D  E  F  G A “A” is Initial Reactant “G” is End Product B, C, D, E, and F are Intermediates

Enzymes  Protein molecules that function as catalysts  The reactants of an enzymatically accelerated reaction are called substrates  Each enzyme accelerates a specific reaction  Each reaction in a metabolic pathway requires a unique and specific enzyme  End product will not appear unless ALL enzymes present and functional 22 E 1 E 2 E 3 E 4 E 5 E 6 A  B  C  D  E  F  G

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6.3 Metabolic Pathways and Enzymes Reactions usually occur in a sequence PProducts of an earlier reaction become reactants of a later reaction SSuch linked reactions form a metabolic pathway Begins with a particular reactant, proceeds through several intermediates, and terminates with a particular end product 24 A  B  C  D  E  F  G “A” is Initial Reactant “G” is End Product B, C, D, E, and F are Intermediates

6.3 Metabolic Pathways and Enzymes Enzyme  Protein molecules that function as catalysts  The reactants of an enzymatically catalyzed reaction are called substrates  Each enzyme accelerates a specific reaction  Each reaction in a metabolic pathway requires a unique and specific enzyme  The end product will not be formed unless ALL enzymes in the pathway are present and functional 25 E 1 E 2 E 3 E 4 E 5 E 6 A  B  C  D  E  F  G

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Energy of Activation Molecules frequently do not react with one another unless they are activated in some way  Energy must be added to at least one reactant to initiate the reaction Energy of activation Enzyme Operation:  Enzymes operate by lowering the energy of activation  Accomplished by bringing substrates into contact with one another 27

Energy of Activation 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Progress of the Reaction energy of reactant energy of product energy of activation (E a ) enzyme not present enzyme present Free Energy energy of activation (E a )

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Enzyme-Substrate Complex The active site complexes with the substrates  Causes the active site to change shape  Shape change forces substrates together, initiating bond  Induced fit model Enzyme is induced to undergo a slight alteration to achieve optimum fit for the substrates 30

Enzyme-Substrate Complex Degradation:  Enzyme complexes with a single substrate molecule  Substrate is broken apart into two product molecules Synthesis:  Enzyme complexes with two substrate molecules  Substrates are joined together and released as a single product molecule 31

Enzymatic Actions 32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Degradation The substrate is broken down to smaller products. products substrate enzyme a. b. active site enzyme-substrate complex enzyme Synthesis The substrates are combined to produce a larger product. product substrates enzyme active site enzyme-substrate complex enzyme

Factors Affecting Enzymatic Speed Substrate concentration  Enzyme activity increases with substrate concentration due to more frequent collisions between substrate molecules and the enzyme Temperature  Enzyme activity increases with temperature  Warmer temperatures cause more effective collisions between enzyme and substrate  However, hot temperatures can denature and destroy enzymes pH  Most enzymes are optimized for a particular pH 33

The Effect of Temperature on Rate of Reaction 34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rate of Reaction (product per unit of time) a.Rate of reaction as a function of temperature b. Body temperature of ectothermic animals often limits rates of reactions. c. Body temperature of endothermic animals promotes rates of reactions. Temperature C b: © James Watt/Visuals Unlimited; c: © Creatas/PunchStock

The Effect of pH on Rate of Reaction 35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rate of Reaction (product per unit of time) pH trypsinpepsin

Factors Affecting Enzymatic Speed Cells can regulate the presence/absence of an enzyme Cells can regulate the concentration of an enzyme Cells can activate or deactivate some enzymes  Enzyme Cofactors Molecules required to activate enzyme Coenzymes are nonprotein organic molecules Vitamins are small organic compounds required in the diet for the synthesis of coenzymes 36

Cofactors at Active Site 37 cofactor active site a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cofactors at Active Site 38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. substrate b.

Cofactors at Active Site 39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cofactor active site substrate b.a.

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Enzyme Inhibition Reversible enzyme inhibition  A substance known as an inhibitor binds to an enzyme and decreases its activity Competitive inhibition – the substrate and the inhibitor are both able to bind to active site Noncompetitive inhibition – the inhibitor does not bind at the active site, but at an allosteric site 41

Noncompetitive Inhibition of an Enzyme 42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 active site enzymes substrates allosteric site E 2 E 3 E 4 E 5 A A F (end product) A Metabolic pathway produces F, the end product. F binds to allosteric site and the active site of E 1 changes shape. A cannot bind to E 1 ; the enzyme has been inhibited by F. BCDE E 1 E 1 E 1 E 1 F 3 1 F (end product) (end product)

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Enzyme Inhibitors Can Spell Death Materials that irreversibly inhibit an enzyme are known as poisons Cyanide inhibits enzymes required for ATP production Sarin inhibits an enzyme located at the neuromuscular junction. Warfarin inhibits an enzyme responsible for the blood clotting process 44

6.4 Organelles and the Flow of Energy Oxidation-reduction (redox) reactions  Electrons pass from one molecule to another Oxidation - loss of an electron Reduction – gain of an electron  Both take place at same time  One molecule accepts the electron given up by the other 45

Photosynthesis and Cellular Respiration 46

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Electron Transport Chain Consists of membrane-bound carrier proteins found in mitochondria and chloroplasts Physically arranged in an ordered series  Starts with high-energy electrons  Pass electrons from one carrier to another Electron energy used to pump hydrogen ions (H + ) to one side of membrane Establishes an electrochemical gradient across the membrane The electrochemical gradient is used to make ATP from ADP – Chemiosmosis  Ends with low-energy electrons and high-energy ATP 48

ElectronTransport Chain 49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. e–e– high-energy electrons High-energy electrons are unstable and have high potential energy. This energy is released in stages, as kinetic energy, during the electron transport chain. electron transport chain low-energy electrons As energy is released, the electrons become more stable and have less potential energy. ATP energy for Synthesis of e-e-

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Chemiosmosis 51 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High H + concentration H + pump in electron transport chain H+H+ Low H + concentration NADH NAD + H+H+ ATP synthase complex

Chemiosmosis 52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High H + concentration H + pump in electron transport chain H+H+ H+H+ H+H+ H+H+ H+H+ Low H + concentration NADH NAD + ATP synthase complex

Chemiosmosis 53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High H + concentration H + pump in electron transport chain H+H+ H+H+ H+H+ H+H+ H+H+ Low H + concentration NADH NAD + ATP synthase complex

Chemiosmosis 54 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P P High H + concentration H + pump in electron transport chain H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Low H + concentration NADH NAD + ATP synthase complex ATP ADP + ATP