Ch06 lecture

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Ch06 lecture

  1. 1. Chapter 6 Energy Flow in the Life of a Cell Lectures by Gregory Ahearn University of North Florida Copyright © 2009 Pearson Education, Inc..
  2. 2. 5.1 What Is Energy?  Energy is the capacity to do work. • Synthesizing molecules • Moving objects • Generating heat and light Copyright © 2009 Pearson Education Inc.
  3. 3. 5.1 What Is Energy?  Types of energy • Kinetic: energy of movement • Potential: stored energy Copyright © 2009 Pearson Education Inc. Fig. 5-1
  4. 4. 5.1 What Is Energy?  First Law of Thermodynamics • “Energy cannot be created nor destroyed, but it can change its form.” • Example: potential energy in gasoline can be converted to kinetic energy in a car, but the energy is not lost Copyright © 2009 Pearson Education Inc.
  5. 5. 5.1 What Is Energy?  Second Law of Thermodynamics • “When energy is converted from one form to another, the amount of useful energy decreases.” • No process is 100% efficient. • Example: more potential energy is in the gasoline than is transferred to the kinetic energy of the car moving • Where is the rest of the energy? It is released in a less useful form as heat—the total energy is maintained. Copyright © 2009 Pearson Education Inc.
  6. 6. 5.1 What Is Energy?  Matter tends to become less organized. • There is a continual decrease in useful energy, and a build up of heat and other nonuseful forms of energy. • Entropy: the spontaneous reduction in ordered forms of energy, and an increase in randomness and disorder as reactions proceed • Example: gasoline is made up of an eightcarbon molecule that is highly ordered • When broken down to single carbons in CO2, it is less ordered and more random. Copyright © 2009 Pearson Education Inc.
  7. 7. 5.1 What Is Energy?  In order to keep useful energy flowing in ecosystems where the plants and animals produce more random forms of energy, new energy must be brought in. Copyright © 2009 Pearson Education Inc.
  8. 8. 5.1 What Is Energy?  Sunlight provides an unending supply of new energy to power all plant and animal reactions, leading to increased entropy. Copyright © 2009 Pearson Education Inc. Fig. 5-2
  9. 9. 5.2 How Does Energy Flow In Chemical Reactions?  Chemical reaction: the conversion of one set of chemical substances (reactants) into another (products) • Exergonic reaction: a reaction that releases energy; the products contain less energy than the reactants Copyright © 2009 Pearson Education Inc.
  10. 10. 5.2 How Does Energy Flow In Chemical Reactions?  Exergonic reaction energy released + reactants + products (a) Exergonic reaction Copyright © 2009 Pearson Education Inc. Fig. 5-3a
  11. 11. 5.2 How Does Energy Flow In Chemical Reactions?  Endergonic reaction: a reaction that requires energy input from an outside source; the products contain more energy than the reactants Copyright © 2009 Pearson Education Inc.
  12. 12. 5.2 How Does Energy Flow In Chemical Reactions?  Endergonic reaction energy used + + products reactants (b) Endergonic reaction Copyright © 2009 Pearson Education Inc. Fig. 5-3b
  13. 13. 5.2 How Does Energy Flow In Chemical Reactions?  Exergonic reactions release energy. • Example: sugar burned by a flame in the presence of oxygen produces carbon dioxide (CO2) and water • Sugar and oxygen contain more energy than the molecules of CO2 and water. • The extra energy is released as heat. Copyright © 2009 Pearson Education Inc.
  14. 14. 5.2 How Does Energy Flow In Chemical Reactions?  Burning glucose releases energy. energy released C6H12O6 (glucose) + 6 O2 (oxygen) 6 CO2 (carbon dioxide) Copyright © 2009 Pearson Education Inc. + 6 H2O (water) Fig. 5-4
  15. 15. 5.2 How Does Energy Flow In Chemical Reactions?  Endergonic reactions require an input of energy. • Example: sunlight energy + CO2 + water in photosynthesis produces sugar and oxygen • The sugar contains far more energy than the CO2 and water used to form it. Copyright © 2009 Pearson Education Inc.
  16. 16. 5.2 How Does Energy Flow In Chemical Reactions?  Photosynthesis requires energy. energy C6H12O6 + 6 O2 (glucose) (oxygen) 6 CO2 (carbon dioxide) + 6 H 2O (water) Copyright © 2009 Pearson Education Inc. Fig. 5-5
  17. 17. 5.2 How Does Energy Flow In Chemical Reactions?  All reactions require an initial input of energy. • The initial energy input to a chemical reaction is called the activation energy. Activation energy needed to ignite glucose high Energy level of reactants energy content of molecules Activation energy captured from sunlight glucose glucose + O2 CO2 + H2O CO2 + H2O Energy level of reactants low progress of reaction (a) Burning glucose (sugar): an exergonic reaction Copyright © 2009 Pearson Education Inc. progress of reaction (b) Photosynthesis: an endergonic reaction Fig. 5-6
  18. 18. 5.2 How Does Energy Flow In Chemical Reactions?  The source of activation energy is the kinetic energy of movement when molecules collide.  Molecular collisions force electron shells of atoms to mingle and interact, resulting in chemical reactions. Copyright © 2009 Pearson Education Inc.
  19. 19. 5.2 How Does Energy Flow in Chemical Reactions?  Exergonic reactions may be linked with endergonic reactions. • Endergonic reactions obtain energy from energy-releasing exergonic reactions in coupled reactions. • Example: the exergonic reaction of burning gasoline in a car provides the endergonic reaction of moving the car • Example: exergonic reactions in the sun release light energy used to drive endergonic sugar-making reactions in plants Copyright © 2009 Pearson Education Inc.
  20. 20. 5.3 How Is Energy Carried Between Coupled Reactions?  The job of transferring energy from one place in a cell to another is done by energycarrier molecules. • ATP (adenosine triphosphate) is the main energy carrier molecule in cells, and provides energy for many endergonic reactions. Copyright © 2009 Pearson Education Inc.
  21. 21. 5.3 How Is Energy Carried Between Coupled Reactions?  ATP is made from ADP (adenosine diphosphate) and phosphate plus energy released from an exergonic reaction (e.g., glucose breakdown) in a cell. energy A A P ADP Copyright © 2009 Pearson Education Inc. P + P phosphate P P P ATP Fig. 5-7
  22. 22. 5.3 How Is Energy Carried Between Coupled Reactions?  ATP is the principal energy carrier in cells. • ATP stores energy in its phosphate bonds and carries the energy to various sites in the cell where energy-requiring reactions occur. • ATP’s phosphate bonds then break yielding ADP, phosphate, and energy. • This energy is then transferred to the energyrequiring reaction. Copyright © 2009 Pearson Education Inc.
  23. 23. 5.3 How Is Energy Carried Between Coupled Reactions?  Breakdown of ATP releases energy. energy A P ATP P P A P ADP Copyright © 2009 Pearson Education Inc. P + P phosphate Fig. 5-8
  24. 24. 5.3 How Is Energy Carried Between Coupled Reactions?  To summarize: • Exergonic reactions (e.g., glucose breakdown) drive endergonic reactions (e.g., the conversion of ADP to ATP). • ATP moves to different parts of the cell and is broken down exergonically to liberate its energy to drive endergonic reactions. Copyright © 2009 Pearson Education Inc.
  25. 25. 5.3 How Is Energy Carried Between Coupled Reactions?  Coupled reactions glucose A exergonic (glucose breakdown) P P P protein endergonic (ATP synthesis) exergonic (ATP breakdown) CO2 + H2O + heat A P P + endergonic (protein synthesis) P amino acids Copyright © 2009 Pearson Education Inc. Fig. 5-9
  26. 26. 5.3 How Is Energy Carried Between Coupled Reactions?  A biological example of coupled reactions • Muscle contraction (an endergonic reaction) is powered by the exergonic breakdown of ATP. • During energy transfer in this coupled reaction, heat is given off, with overall loss of usable energy. Copyright © 2009 Pearson Education Inc.
  27. 27. 5.3 How Is Energy Carried Between Coupled Reactions?  ATP breakdown is coupled with muscle contraction. Exergonic reaction: ATP Endergonic reaction: + 20 units energy relaxed muscle contracted muscle 100 units + ADP + P energy released Energy released from ATP breakdown exceeds the energy used for muscle contraction, so the overall coupled reaction is exergonic Coupled reaction: + relaxed muscle Copyright © 2009 Pearson Education Inc. ATP + 80 units energy contracted released muscle as heat + ADP + P Fig. 5-10
  28. 28. 5.3 How Is Energy Carried Between Coupled Reactions? PLAY Animation—Energy and Chemical Reactions Copyright © 2009 Pearson Education Inc.
  29. 29. 5.3 How Is Energy Carried Between Coupled Reactions?  Electron carriers also transport energy within cells. • Besides ATP, other carrier molecules transport energy within a cell. • Electron carriers capture energetic electrons transferred by some exergonic reaction. • Energized electron carriers then donate these energy-containing electrons to endergonic reactions. Copyright © 2009 Pearson Education Inc.
  30. 30. 5.3 How Is Energy Carried Between Coupled Reactions?  Common electron carriers are NAD+ and FAD. high-energy reactants energized e– NADH depleted low-energy products Copyright © 2009 Pearson Education Inc. e– high-energy products NAD+ + H+ low-energy reactants Fig. 5-11
  31. 31. 5.3 How Is Energy Carried Between Coupled Reactions? PLAY Animation—Energy and Life Copyright © 2009 Pearson Education Inc.
  32. 32. 5.4 How Do Cells Control Their Metabolic Reactions?  Cell metabolism: the multitude of chemical reactions going on at any specific time in a cell  Metabolic pathways: the sequence of cellular reactions (e.g., photosynthesis and glycolysis) Initial reactant PATHWAY 1 A B enzyme 1 D C enzyme 2 enzyme 3 E enzyme 4 G F PATHWAY 2 enzyme 5 Copyright © 2009 Pearson Education Inc. Final products Intermediates enzyme 6 Fig. 5-12
  33. 33. 5.4 How Do Cells Control Their Metabolic Reactions?  At body temperature, many spontaneous reactions proceed too slowly to sustain life. • A reaction can be controlled by controlling its activation energy (the energy needed to start the reaction). • At body temperature, reactions occur too slowly because their activation energies are too high. • Molecules called catalysts are able to gain access to energy that is not produced spontaneously. Copyright © 2009 Pearson Education Inc.
  34. 34. 5.4 How Do Cells Control Their Metabolic Reactions?  Catalysts reduce activation energy. • Catalysts are molecules that speed up a reaction without being used up or permanently altered. • They speed up the reaction by reducing the activation energy. high Activation energy without catalyst energy content of molecules Activation energy with catalyst reactants products low progress of reaction Copyright © 2009 Pearson Education Inc. Fig. 5-13
  35. 35. 5.4 How Do Cells Control Their Metabolic Reactions?  Three important principles about all catalysts • Catalysts speed up a reaction. • They speed up reactions that would occur anyway, if their activation energy could be surmounted. • Catalysts are not altered by the reaction. Copyright © 2009 Pearson Education Inc.
  36. 36. 5.4 How Do Cells Control Their Metabolic Reactions?  Enzymes are biological catalysts. • Almost all enzymes are proteins. • Enzymes are highly specialized, generally catalyzing only a single reaction. • In metabolic pathways involving multiple reactions, each reaction is catalyzed by a different enzyme. Copyright © 2009 Pearson Education Inc.
  37. 37. 5.4 How Do Cells Control Their Metabolic Reactions?  The structure of enzymes allows them to catalyze specific reactions. • Enzymes have an active site where the reactant molecules, called substrates, enter and undergo a chemical change as a result. • The specificity of an enzyme reaction is due to the distinctive shape of the active site, which only allows proper substrate molecules to enter. Copyright © 2009 Pearson Education Inc.
  38. 38. 5.4 How Do Cells Control Their Metabolic Reactions?  How does an enzyme catalyze a reaction? • Both substrates enter the enzyme’s active site. • Substrates enter an enzyme’s active site, changing both of their shapes. • The chemical bonds are altered in the substrates, promoting the reaction. • The substrates change into a new form that will not fit the active site, and so are released. Copyright © 2009 Pearson Education Inc.
  39. 39. 5.4 How Do Cells Control Their Metabolic Reactions?  The cycle of enzyme–substrate interactions substrates active site of enzyme enzyme 1 Substrates enter the active site in a specific orientation 3 The substrates, bonded together, leave the enzyme; the enzyme is ready for a new set of substrates Copyright © 2009 Pearson Education Inc. 2 The substrates and active site change shape, promoting a reaction between the substrates Fig. 5-14
  40. 40. 5.4 How Do Cells Control Their Metabolic Reactions? PLAY Animation—Enzymes Copyright © 2009 Pearson Education Inc.
  41. 41. 5.4 How Do Cells Control Their Metabolic Reactions?  Cells regulate metabolism by controlling enzymes. • Allosteric regulation can increase or decrease enzyme activity. • In allosteric regulation, an enzyme’s activity is modified by a regulator molecule. • The regulator molecule binds to a special regulatory site on the enzyme separate from the enzyme’s active site. Copyright © 2009 Pearson Education Inc.
  42. 42. 5.4 How Do Cells Control Their Metabolic Reactions?  Binding of the regulator molecule modifies the active site on the enzyme, causing the enzyme to become more or less able to bind substrate.  Thus, allosteric regulation can either promote or inhibit enzyme activity. Copyright © 2009 Pearson Education Inc.
  43. 43. 5.4 How Do Cells Control Their Metabolic Reactions?  Enzyme structure substrate active site Many enzymes have both active sites and allosteric regulatory sites enzyme (a) Enzyme structure Copyright © 2009 Pearson Education Inc. allosteric regulatory site Fig. 5-15a
  44. 44. 5.4 How Do Cells Control Their Metabolic Reactions?  Allosteric inhibition An allosteric regulator molecule causes the active site to change shape, so the substrate no longer fits (b) Allosteric inhibition Copyright © 2009 Pearson Education Inc. allosteric regulator molecule Fig. 5-15b
  45. 45. 5.4 How Do Cells Control Their Metabolic Reactions?  Competitive inhibition can be temporary or permanent.  Some regulatory molecules temporarily bind directly to an enzyme’s active site, preventing the substrate molecules from binding.  These molecules compete with the substrate for access to the active site, and control the enzyme by competitive inhibition. Copyright © 2009 Pearson Education Inc.
  46. 46. 5.4 How Do Cells Control Their Metabolic Reactions?  Competitive inhibition A competitive inhibitor molecule occupies the active site and blocks entry of the substrate Copyright © 2009 Pearson Education Inc. Fig. 5-16

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