Chapter 6 Metabolism

Two Laws of Thermodynamics Biology, 9th ed,Sylvia Mader Chapter 06 Two Laws of Thermodynamics Metabolism 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

6.2 Metabolic Reactions and Energy Transformations Biology, 9th ed,Sylvia Mader Chapter 06 6.2 Metabolic Reactions and Energy Transformations Metabolism 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)

Biology, 9th ed,Sylvia Mader Chapter 06 ATP: Energy for Cells Metabolism Adenosine triphosphate (ATP) High energy compound used to drive metabolic reactions Constantly being generated from adenosine diphosphate (ADP) Composed of: Adenine, ribose (together = adenosine), and three phosphate groups Coupled reactions Energy released by an exergonic reaction captured in ATP ATP is used to drive an endergonic reaction

The ATP Cycle 5 Metabolism Biology, 9th ed,Sylvia Mader Chapter 06 Slide #5 Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. adenosine triphosphate ATP is unstable and has a high potential energy. P P P Exergonic Reaction: • Creation of ATP from ADP and Prequires input of energy from Other sources. ATP • Has positive delta G. • Example: cellular respiration ADP + P Endergonic 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 P P + P 5 adenosine diphosphate + phosphate ADP is more stable and has lower potential energy than ATP.

6.3 Metabolic Pathways and Enzymes Biology, 9th ed,Sylvia Mader Chapter 06 6.3 Metabolic Pathways and Enzymes Metabolism Reactions 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 AB C D E FG “A” is Initial Reactant B, C, D, E, and F are Intermediates “G” is End Product

6.3 Metabolic Pathways and Enzymes Biology, 9th ed,Sylvia Mader Chapter 06 6.3 Metabolic Pathways and Enzymes Metabolism 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 E1 E2 E3 E4 E5 E6 A  B  C  D  E  F  G

Biology, 9th ed,Sylvia Mader Chapter 06 Energy of Activation Metabolism 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

Biology, 9th ed,Sylvia Mader Chapter 06 Energy of Activation Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. energy of activation (Ea) energy of reactant energy of activation (Ea) Free Energy energy of product enzyme not present enzyme present Progress of the Reaction

Enzyme-Substrate Complex Biology, 9th ed,Sylvia Mader Chapter 06 Enzyme-Substrate Complex Metabolism 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

Enzyme-Substrate Complex Biology, 9th ed,Sylvia Mader Chapter 06 Enzyme-Substrate Complex Metabolism 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

Biology, 9th ed,Sylvia Mader Enzymatic Actions Chapter 06 Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. products enzyme substrate enzyme-substrate complex active site Degradation The substrate is broken down to smaller products. a. enzyme product enzyme substrates enzyme-substrate complex active site Synthesis The substrates are combined to produce a larger product. b. enzyme

Factors Affecting Enzymatic Speed Biology, 9th ed,Sylvia Mader Chapter 06 Factors Affecting Enzymatic Speed Metabolism 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

The Effect of Temperature on Rate of Reaction Biology, 9th ed,Sylvia Mader Chapter 06 The Effect of Temperature on Rate of Reaction Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (product per unit of time) Rate of Reaction 0 10 20 30 40 50 60 Temperature C 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. b: © James Watt/Visuals Unlimited; c: © Creatas/PunchStock

The Effect of pH on Rate of Reaction Biology, 9th ed,Sylvia Mader Chapter 06 The Effect of pH on Rate of Reaction Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pepsin trypsin (product per unit of time) Rate of Reaction 1 2 3 4 5 6 7 8 9 10 1 1 12 pH

Factors Affecting Enzymatic Speed Biology, 9th ed,Sylvia Mader Chapter 06 Factors Affecting Enzymatic Speed Metabolism 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

Cofactors at Active Site Biology, 9th ed,Sylvia Mader Chapter 06 Slide #17 Cofactors at Active Site Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cofactor active site substrate a. b. 17

Biology, 9th ed,Sylvia Mader Chapter 06 Enzyme Inhibition Metabolism 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

Noncompetitive Inhibition of an Enzyme Biology, 9th ed,Sylvia Mader Noncompetitive Inhibition of an Enzyme Chapter 06 Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A E allosteric site 1 enzymes substrates E 1 E 2 E 3 E 4 E 5 F A B C D E (end product) 1 Metabolic pathway produces F, the end product. F active site E (end product) 1 2 F binds to allosteric site and the active site of E1 changes shape. F A E (end product) 1 3 A cannot bind to E1; the enzyme has been inhibited by F.

Enzyme Inhibitors Can Spell Death Biology, 9th ed,Sylvia Mader Chapter 06 Enzyme Inhibitors Can Spell Death Metabolism 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

6.4 Organelles and the Flow of Energy Biology, 9th ed,Sylvia Mader Chapter 06 6.4 Organelles and the Flow of Energy Metabolism 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

Photosynthesis and Cellular Respiration Biology, 9th ed,Sylvia Mader Chapter 06 Photosynthesis and Cellular Respiration Metabolism

Electron Transport Chain Biology, 9th ed,Sylvia Mader Chapter 06 Electron Transport Chain Metabolism 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

ElectronTransport Chain Biology, 9th ed,Sylvia Mader ElectronTransport Chain Chapter 06 Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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. energy for Synthesis of ATP electron transport chain As energy is released, the electrons become more stable and have less potential energy. low-energy electrons e-

Chemiosmosis 25 High H+ concentration H+ H+ H+ pump in electron Biology, 9th ed,Sylvia Mader Chemiosmosis Chapter 06 Slide #25 Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High H+ concentration H+ H+ H+ pump in electron transport chain H+ H+ H+ ATP ADP + P ATP synthase complex ADP + P NADH NAD + H+ ATP H+ Low H+ concentration 25