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Ch.08An Introduction to Metabolism

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Ch.08An Introduction to Metabolism A diver has more potential Diving converts energy on the platform potential energy to than in the water. kinetic energy. Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting Product molecule Climbing up converts the kinetic A diver has less potential energy of muscle movement energy in the water to potential energy. than on the platform. 1 2 • More free energy (higher G) • Less stable • Greater work capacity Heat CO2 In a spontaneous change + • The free energy of the system Chemical H O decreases (∆G < 0) energy 2 • The system becomes more stable • The released free energy can be harnessed to do work • Less free energy (lower G) • More stable (a) First law of thermodynamics (b) Second law of thermodynamics • Less work capacity (a) Gravitational motion (b) Diffusion (c) Chemical reaction 3 4 Reactants ∆G < 0 ∆G = 0 Amount of energy released (∆G < 0) Energy Products (a) An isolated hydroelectric system Free energy (b) An open hydroelectric system Progress of the reaction ∆G < 0 (a) Exergonic reaction: energy released Products Amount of energy ∆G < 0 required ∆G < 0 (∆G > 0) ∆G < 0 Energy Reactants Free energy Progress of the reaction (b) Endergonic reaction: energy required (c) A multistep open hydroelectric system 5 6 Adenine P P P Adenosine triphosphate (ATP) H2O Phosphate groups Ribose + P i P P + Energy Inorganic phosphate Adenosine diphosphate (ADP) 7 8 NH2 Membrane protein NH + 3 ∆G = +3.4 kcal/mol Glu Glu Glutamic Ammonia Glutamine acid (a) Endergonic reaction P P i Solute Solute transported 1 ATP phosphorylates P glutamic acid, + ATP + ADP (a) Transport work: ATP phosphorylates Glu Glu making the amino transport proteins ADP acid less stable. ATP + NH2 P i P Vesicle Cytoskeletal track 2 Ammonia displaces NH + 3 + P the phosphate group, Glu Glu i forming glutamine. (b) Coupled with ATP hydrolysis, an exergonic reaction ATP Motor protein Protein moved (b) Mechanical work: ATP binds noncovalently (c) Overall free-energy change to motor proteins, then is hydrolyzed 9 10 ATP + H2O Sucrose (C12H22O11) Sucrase Energy from Energy for cellular catabolism (exergonic, work (endergonic, energy-releasing ADP + P i energy-consuming processes) processes) Glucose (C6H12O6) Fructose (C6H12O6) 11 12 A B Course of C D reaction E Transition state without A enzyme without enzyme EA with enzyme A B EA is lower Reactants C D Reactants Course of Free energy ∆G is unaffected reaction A B by enzyme with enzyme ∆G < O Free energy C D Products Products Progress of the reaction Progress of the reaction 13 14 1 Substrates enter active site; enzyme changes shape such that its active site 2 Substrates held in enfolds the substrates (induced fit). active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrate Substrates Enzyme-substrate complex 3 Active site can lower EA and speed up a reaction. Active site 6 Active site is available for two new substrate molecules. Enzyme Enzyme Enzyme-substrate complex (a) (b) 5 Products are 4 Substrates are released. converted to products. Products 15 16 Optimal temperature for Optimal temperature for typical human enzyme enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction Substrate 0 20 40 60 80 100 Temperature (ºC) Active site (a) Optimal temperature for two enzymes Competitive inhibitor Optimal pH for pepsin Optimal pH Enzyme (stomach enzyme) for trypsin (intestinal enzyme) Noncompetitive inhibitor (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Rate of reaction 0 1 2 3 4 5 6 7 8 9 10 pH (b) Optimal pH for two enzymes 17 18 Allosteric enyzme Active site with four subunits (one of four) Initial substrate (threonine) Active site available Threonine Regulatory in active site site (one Activator of four) Active form Stabilized active form Enzyme 1 (threonine Isoleucine deaminase) used up by Oscillation cell Intermediate A Feedback Enzyme 2 inhibition Active site of enzyme 1 no longer binds Intermediate B threonine; pathway is Enzyme 3 Non- Inhibitor switched off. functional Inactive form Stabilized inactive active form site Intermediate C Isoleucine (a) Allosteric activators and inhibitors binds to Enzyme 4 allosteric Substrate site Intermediate D Enzyme 5 Inactive form Stabilized active End product form (isoleucine) (b) Cooperativity: another type of allosteric activation 19 20 .
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