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Chapter 6 • Energy Flow in the Life of a Cell Copyright © 2005 Pearson Prentice Hall, Inc. Energy? • ABILITY TO DO WORK – potential (stored) kinetic (active) (the diver illustration) • “Acts” According to 2 “Rules” – First Law of Thermodynamics Energy Cannot be Created or Destroyed OR Energy Can Only be Converted from 1 Form to Another OR “YOU CAN’T WIN” – Second Law of Thermodynamics Every Process Generates Some Unusable Energy (= Heat) Every System “Wants” To Get To Its Lowest Energy State OR “YOU CAN’T BREAK EVEN” OR • Organisms Are Organized = High Energy State – 2nd Law Constantly “Driving Them Down” – Therefore Organisms Constanly Use Energy to Stay Organized Copyright © 2005 Pearson Prentice Hall, Inc. Energy? • ABILITY TO DO WORK – potential (stored) kinetic (active) Unnumbered (diver) • “Acts” According to 2 “Rules” – First Law of Thermodynamics Energy Cannot be Created or Destroyed Energy Can Only be Converted from 1 Form to Another “YOU CAN’T WIN” – Second Law of Thermodynamics Every Process Generates Unusable Energy (= Heat) Every System “Wants” To Get To Its Lowest Energy State “YOU CAN’T BREAK EVEN” • Organisms Are Organized = High Energy State – 2nd Law Constantly “Driving Them Down” – Therefore Organisms Constanly Use Energy to Stay Organized Copyright © 2005 Pearson Prentice Hall, Inc. gas 100 units chemical energy (concentrated) 75 units heat energy 25 units kinetic energy (motion) How Do Organisms Constantly Use Energy to Stay Organized? • By Reaction Coupling 2 Types of Reactions: – Exergonic – Release Energy – Endergonic – Take In Energy – Energy relations in exergonic and endergonic reactions – Organisms Use the Energy of Sunlight to Maintain The Highly Organized (=Low-Entropy) Condition Known as Life • Carry Out Reaction Coupling By Energy Carriers: Copyright © 2005 Pearson Prentice Hall, Inc. Exergonic reaction energy released reactants products Endergonic reaction energy used products reactants Burning glucose energy released 6 O O glucose oxygen 6 O C O carbon dioxide 6 H O H water Photosynthesis energy 6 O O 6 O C O carbon dioxide 6 H glucose O H water oxygen Burning glucose (sugar): an exergonic reaction high Photosynthesis: an endergonic reaction high activation energy needed to ignite glucose energy content of molecules glucose + O2 energy released by burning glucose energy content of molecules CO2 + H2O low activation energy from light captured by photosynthesis CO2 + H2O low progress of reaction progress of reaction glucose net energy captured by synthesizing glucose Exergonic reaction: ATP 100 units ADP energy released P 80 units energy ADP released as heat P Endergonic reaction: 20 units energy contracted muscle relaxed muscle Coupled reaction: ATP relaxed muscle contracted muscle Exergonic reaction: + ADP 100 units energy released ATP + P ADP + P Endergonic reaction: + 20 units energy contracted muslce relaxed muscle Coupled reaction: + relaxed muscle + 80 units energy + released as heat ATP contracted muslce 6.3 How Is Cellular Energy Carried Between Coupled Reactions? • 6.3.1 ATP Is the Principal Energy Carrier in Cells – Figure 6.4 ADP and ATP (p. 104) – Unnumbered Figure 6 (Hide/Reveal) ATP synthesis: Energy is stored in ATP (p. 104) – Unnumbered Figure 7 (Hide/Reveal) ATP breakdown: Energy of ATP is released (p. 104) – Figure 6.5 Coupled reactions within living cells (p. 105) Copyright © 2005 Pearson Prentice Hall, Inc. Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) NH2 adenine N C C NH22 "high-energy” bond N N C C N N C CH "high-energy” bonds HC HC N C N CH O– O CH2 ribose H H H OH OH Shorthand representations A Energy content O P H O– H O phosphate groups low P or ADP A H H OH OH P O– O– O P O– O O P N O CH2 H P O O P O O– O P O– O phosphate groups P P high or ATP Adenosine diphosphate (ADP) NH2 adenine N C C N N C CH "high-energy” bond HC N O– O CH2 H ribose H Shorthand representations Energy content H H OH OH A O P O– P O– O O O phosphate groups P low P or ADP Adenosine triphosphate (ATP) NH2 N C C "high-energy” bonds N HC N C N CH O H A H H OH OH P O– O– O CH2 H P O O P O O– O P O– O phosphate groups P P high or ATP ATP synthesis: Energy is stored in ATP energy A A P ADP P P phosphate P ATP P P ATP synthesis: Energy is stored in ATP energy A A P ATP P ADP P P phosphate P P ATP breakdown: Energy of ATP is released energy A P P P ATP A P ADP P P phosphate ATP breakdown: Energy of ATP is released energy A P P P ATP A P ADP P P phosphate Coupled reaction: glucose breakdown and protein synthesis glucose A exergonic (glucose breakdown) P P P protein endergonic (ATP synthesis) exergonic (ATP breakdown) endergonic (protein synthesis) CO2 + H2O + heat A P P P ADP net exergonic "downhill" reaction heat amino acids 6.3 How Is Cellular Energy Carried Between Coupled Reactions? • 6.3.2 Electron Carriers Also Transport Energy Within Cells – Figure 6.6 Electron carriers (p. 105) Copyright © 2005 Pearson Prentice Hall, Inc. Electron carrier molecules transport energy NADH exergonic reaction _ (energized carrier) e _ e (depleted carrier) NAD+ H net exergonic "downhill" reaction endergonic reaction 6.4 How Do Cells Control Their Metabolic Reactions? • Figure 6.7 Simplified view of metabolic pathways (p. 106) Copyright © 2005 Pearson Prentice Hall, Inc. Initial reactant PATHWAY 1 A D C B enzyme 1 Final products Intermediates enzyme 2 enzyme 3 PATHWAY 2 E enzyme 4 F enzyme 5 G enzyme 6 6.4 How Do Cells Control Their Metabolic Reactions? • 6.4.1 At Body Temperatures, Spontaneous Reactions Proceed Too Slowly to Sustain Life • 6.4.2 Catalysts Reduce Activation Energy – Figure 6.8 Catalysts lower activation energy, increasing the rate of reactions (p. 106) Copyright © 2005 Pearson Prentice Hall, Inc. high activation energy without catalyst energy content of molecules activation energy with catalyst reactants products low progress of reaction 6.4 How Do Cells Control Their Metabolic Reactions? • 6.4.3 Enzymes Are Biological Catalysts • 6.4.4 The Structure of Enzymes Allows Them to Catalyze Specific Reactions – Figure 6.9 The cycle of enzyme–substrate interactions (p. 107) Copyright © 2005 Pearson Prentice Hall, Inc. substrates active site of enzyme enzyme substrates active site of enzyme enzyme 6.4 How Do Cells Control Their Metabolic Reactions? • 6.4.5 Cells Regulate the Amount and the Activity of Their Enzymes – Figure 6.10 Enzyme regulation by feedback inhibition (p. 108) – Figure 6.11 Enzyme regulation by allosteric regulation and competitive inhibition (p. 109) Copyright © 2005 Pearson Prentice Hall, Inc. CH3 CH3 H C OH H C NH3 CH2 A B enzyme 1 enzyme 2 enzyme 3 C D enzyme 4 COOH threonine (substrate amino acid) enzyme 5 H C CH3 H C NH3 COOH Feedback inhibition: Isoleucine inhibits enzyme 1 isoleucine (end-product amino acid) Enzyme structure substrate active site enzyme allosteric regulatory site Allosteric inhibition Competitive inhibition allosteric regulator molecule Enzyme structure substrate active site enzyme allosteric regulatory site Allosteric inhibition Competitive inhibition allosteric regulator molecule 6.4 How Do Cells Control Their Metabolic Reactions? • 6.4.6 The Activity of Enzymes Is Influenced by Their Environment Copyright © 2005 Pearson Prentice Hall, Inc.