Chapter 8 An Introduction to MetabolismPowerPoint® Lecture Presentations for        Biology       Eighth EditionNeil Campb...
An organism’s metabolism transforms matter andenergy, subject to the laws of thermodynamics• Metabolism is the totality of...
Catabolic vs Anabolic Pathways• Catabolic pathways       – release energy by breaking down complex molecules         into ...
Forms of Energy• Energy is the capacity to cause change or do  work and can be converted from one form to  another       –...
A diver has more potential energy        Diving converts potential energy    on the platform than in the water.       to k...
The Laws of Energy Transformation• Thermodynamics is the study of energy  transformations• A closed system is isolated fro...
The Laws of Thermodynamics•    First Law of Thermodynamics       –      Energy can be transferred and transformed, but it ...
Fig. 8-3             First and Second law of Thermodynamics                                                               ...
Biological Order and Disorder• Cells create ordered structures from less ordered materials       – Ex: amino acids make pr...
The free-energy change of a reaction tells uswhether or not the reaction occurs spontaneously• Free Energy       – energy ...
Free-Energy Change, ∆G• Equilibrium is a state of maximum stability• Spontaneous reactions:       •       ∆G < 0 (a negati...
Relationship of free energy to stability, work capacity and     spontaneous change                                        ...
Exergonic and Endergonic Reactions in Metabolism• An exergonic reaction (downhill) proceeds with a net  release of free en...
Fig. 8-6                                          Reactants                                                               ...
Equilibrium and Metabolism• Reactions in a closed system eventually reach equilibrium  and then do no work       –       C...
Fig. 8-7                                                               ∆G < 0                    ∆G = 0An isolated hydroel...
Practice Quiz                                        A                B•   Which one of these is the best example of a    ...
ATP powers cellular work by coupling exergonicreactions to endergonic reactions• A cell does three main kinds of work whic...
The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate)       –        is the cell’s energy shuttle       – comp...
The Structure and Hydrolysis of ATP• Hydrolysis can break the bonds between  phosphate groups of ATP• Energy is released f...
Fig. 8-9                            P   P    P                           Adenosine triphosphate (ATP)                     ...
How ATP Performs Work• Mechanical, transport, and chemical work are  powered by the hydrolysis of ATP• The energy from the...
NH2(a) Endergonic reaction                                                        NH3                                     ...
Fig. 8-11                                 Membrane protein) Transport work:TP phosphorylatesansport proteins              ...
The Regeneration of ATP• ATP is a renewable resource       – ADP + Pi  ATP• The energy to phosphorylate ADP comes from  c...
Fig. 8-12       Energy coupling and the renewal of ATP ATP synthesis                                      ATP hydrolysisre...
Enzymes speed up metabolic reactions by loweringenergy barriers• A catalyst is a chemical  agent that speeds up a  reactio...
The Activation Energy Barrier• Every chemical reaction between molecules  involves bond breaking and bond forming• Free en...
Fig. 8-14     Energy profile of an exergonic reaction (spontaneous)                                      AB + CD  AC + BD...
Fig. 8-15                    The effect of an enzyme on activation energy                   Course of                   re...
Substrate Specificity of Enzymes• The reactant that an enzyme acts on is called  the enzyme’s substrate• The enzyme binds ...
Fig. 8-16                Induced fit between an enzyme and its substrate   Substrate  Active site                     Enzy...
Catalysis in the Enzyme’s Active Site• substrate binds to the active site• The active site can lower an EA barrier by     ...
Fig. 8-17              1 Substrates enter active site; enzyme              changes shape such that its active site        ...
Cofactors• Cofactors are nonprotein enzyme helpers• Cofactors may be inorganic (such as a metal in  ionic form) or organic...
Effects of Local Conditions on Enzyme Activity• An enzyme’s activity can be affected by       – pH       – Temperature    ...
Fig. 8-18                                   Optimal temperature for   Optimal temperature for                             ...
Enzyme Inhibitors• Competitive inhibitors bind to the active site  of an enzyme, competing with the substrate• Noncompetit...
Fig. 8-19                      Types of Enzyme Inhibition                      Substrate                      Active site ...
Regulation of enzyme activity helps controlmetabolism• Metabolic pathways are tightly regulated       – Allosteric regulat...
Allosteric Regulation of Enzymes• Enzymes are made up of several subunits or polypeptide  chains which have there own acti...
Allosteric Regulation of Enzymestors and inhibitors (bind to regulatory sites)        Allosteric enyzme        Active site...
Initial substrate         Feedback                                   Active site                                          ...
Practice Quiz1.   Lists the three components of ATP.2.   ________ reactions release energy while ________ reactions absorb...
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Chapter 8(1)

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  • Figure 8.2 Transformations between potential and kinetic energy
  • Figure 8.3 The two laws of thermodynamics
  • Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change
  • Figure 8.6 Free energy changes ( Δ G ) in exergonic and endergonic reactions
  • Figure 8.7 Equilibrium and work in isolated and open systems
  • For the Cell Biology Video Space Filling Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
  • For the Cell Biology Video Stick Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
  • Figure 8.9 The hydrolysis of ATP
  • Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis
  • Figure 8.11 How ATP drives transport and mechanical work
  • Figure 8.12 The ATP cycle
  • Figure 8.14 Energy profile of an exergonic reaction
  • Figure 8.15 The effect of an enzyme on activation energy
  • For the Cell Biology Video Closure of Hexokinase via Induced Fit, go to Animation and Video Files.
  • Figure 8.16 Induced fit between an enzyme and its substrate
  • Figure 8.17 The active site and catalytic cycle of an enzyme
  • Figure 8.18 Environmental factors affecting enzyme activity
  • Figure 8.19 Inhibition of enzyme activity
  • Figure 8.20 Allosteric regulation of enzyme activity
  • Figure 8.22 Feedback inhibition in isoleucine synthesis
  • Chapter 8(1)

    1. 1. Chapter 8 An Introduction to MetabolismPowerPoint® Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan SharpCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    2. 2. An organism’s metabolism transforms matter andenergy, subject to the laws of thermodynamics• Metabolism is the totality of an organism’s chemical reactions – Example of an emergent property that arises from interactions between molecules within the cell• A metabolic pathway begins with a specific molecule and ends with a product – Each step is catalyzed by a specific enzyme Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3Starting Productmolecule
    3. 3. Catabolic vs Anabolic Pathways• Catabolic pathways – release energy by breaking down complex molecules into simpler compounds – Ex: Cellular respiration (the breakdown of glucose in the presence of oxygen)• Anabolic pathways – consume energy to build complex molecules from simpler ones – Ex: The synthesis of protein from amino acidsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    4. 4. Forms of Energy• Energy is the capacity to cause change or do work and can be converted from one form to another – Kinetic energy (energy of movement) – Heat (thermal energy) – Potential energy – Chemical energyCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    5. 5. A diver has more potential energy Diving converts potential energy on the platform than in the water. to kinetic energy.Climbing up converts the kinetic energy A diver has less potential energyof muscle movement to potential energy. in the water than on the platform.
    6. 6. The Laws of Energy Transformation• Thermodynamics is the study of energy transformations• A closed system is isolated from its surroundings – Ex: liquid in a thermos• In an open system, energy and matter can be transferred between the system and its surroundings – Ex: Organisms absorb energy and release heatCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    7. 7. The Laws of Thermodynamics• First Law of Thermodynamics – Energy can be transferred and transformed, but it cannot be created or destroyed – The energy of the universe is constant – “principle of conservation of energy” – Ex: plants convert sunlight to chemical energy• Second Law of Thermodynamics – During every energy transfer or transformation, some energy is unusable, and is often lost as heat – Every energy transfer or transformation increases the entropy (disorder) of the universeCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    8. 8. Fig. 8-3 First and Second law of Thermodynamics Heat CO2 + Chemical H2O energy (a) First law of thermodynamics (b) Second law of thermodynamics
    9. 9. Biological Order and Disorder• Cells create ordered structures from less ordered materials – Ex: amino acids make proteins• Organisms also replace ordered forms of matter and energy with less ordered forms – Ex: the break down of food molecules produces water, heat and CO2• Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases• Energy flows into an ecosystem in the form of light and exits as heatCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    10. 10. The free-energy change of a reaction tells uswhether or not the reaction occurs spontaneously• Free Energy – energy that can do work when temperature and pressure are uniform, as in a living cell – measure of a system’s instability• The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T): Free energy change: ∆G = ∆H – T∆S Free Total Temp Entropy energy energy (K)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    11. 11. Free-Energy Change, ∆G• Equilibrium is a state of maximum stability• Spontaneous reactions: • ∆G < 0 (a negative ∆G) • can be harnessed to perform work when it is moving towards equillibrium • free energy decreases and the stability of a system increases• ∆G represents the difference between the free energy of the final state and the free energy of the initial state ∆G = Gfinal state – Ginitial stateCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    12. 12. Relationship of free energy to stability, work capacity and spontaneous change Unstable systems • More free energy (higher G) • Less stable • Greater work capacity In a spontaneous change: • The free energy of the system decreases (∆G < 0) • The system becomes more stable• The released free energy can be harnessed to do work • Less free energy (lower G) • More stable • Less work capacity (c) Chemical reaction (a) Gravitational motion (b) Diffusion
    13. 13. Exergonic and Endergonic Reactions in Metabolism• An exergonic reaction (downhill) proceeds with a net release of free energy and is spontaneous – ∆G is negative – The greater the decrease in free energy, the more work can be done• An endergonic reaction (uphill) absorbs free energy from its surroundings and is nonspontaneous – ∆G is positive and is the energy required to drive the reaction• If a chemical process is exergonic/downhill then the opposite reaction must be endergonic/uphillCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    14. 14. Fig. 8-6 Reactants Amount of energy released Exergonic reation: Free energy (∆G < 0) energy released Energy Products Progress of the reaction Products Amount of energy Endergonic reation: required Free energy (∆G > 0) energy required Energy Reactants Progress of the reaction
    15. 15. Equilibrium and Metabolism• Reactions in a closed system eventually reach equilibrium and then do no work – Cells are not in equilibrium; they are open systems experiencing a constant flow of materials• In life metabolism is never at equilibrium• A catabolic pathway in a cell releases free energy in a series of reactions• Closed and open hydroelectric systems can serve as analogies What would happen if a cell was in equilibrium?Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    16. 16. Fig. 8-7 ∆G < 0 ∆G = 0An isolated hydroelectric system •Downhill flow of water turns a turbine •turbine drives a generator •Electricity turns on a light bulb •Eventually equilibrium will be reached Spontaneous reaction (b) An open hydroelectric system ∆G < 0 •Running water powers the generator •Intake and outflow of water keeps equilibrium from occurring •Electricity turns on a light bulb c) A multistep open hydroelectric ∆G < 0system ∆G < 0 •Running water powers the generator ∆G < 0 •The product becomes the reactant in the next reaction •Equilibrium will not be reached •Ex: cellular respiration Similar to a catabolic pathway that releases energy
    17. 17. Practice Quiz A B• Which one of these is the best example of a spontaneous reaction?• Which one is more unstable?• Which reaction is uphill? Which is downhill?• Which reaction is endergonic? Exergonic?• Which one will require more energy for work? Stable Unstable• Which one has a +∆G? Uphill Downhill Less work More work• Which one has a -∆G? Low ∆G High ∆G ∆G increases ∆G decreases• In B, is the ∆G going to decrease or increase? Nonspontaneous Spontaneous Endergonic Exergonic Absorbs energy Releases energy
    18. 18. ATP powers cellular work by coupling exergonicreactions to endergonic reactions• A cell does three main kinds of work which all require energy: – Chemical – the pushing of endergonic rxns that require energy – Transport – pump substances across membranes against a gradient – Mechanical – ex: muscle contraction, beating of cilia• To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one – Most energy coupling in cells is mediated by ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    19. 19. The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate) – is the cell’s energy shuttle – composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups Adenine Phosphate groups RiboseCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    20. 20. The Structure and Hydrolysis of ATP• Hydrolysis can break the bonds between phosphate groups of ATP• Energy is released from ATP when the terminal phosphate bond is broken (exergonic rxn)• This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves ATP  ADP + Pi + Energy Higher ∆G  Lower ∆G (more stable)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    21. 21. Fig. 8-9 P P P Adenosine triphosphate (ATP) H2O Pi + P P + Energy Inorganic phosphate Adenosine diphosphate (ADP) ATP + H20  ADP + Pi ∆G = -7.3 kcal/mol Exergonic
    22. 22. How ATP Performs Work• Mechanical, transport, and chemical work are powered by the hydrolysis of ATP• The energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction• Overall, the coupled reactions are exergonic• ATP drives endergonic reactions by phosphorylationCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    23. 23. NH2(a) Endergonic reaction NH3 Glu + ∆G = +3.4 kcal/mol Glu Glutamic Ammonia Glutamine acid P(b) Coupled with ATP hydrolysis, + + ADP an exergonic reaction ATP Glu Glu 1 ATP phosphorylates glutamic acid, making the amino acid less stable NH2 (exergonic). P 2 Ammonia displaces the phosphate + NH3 + Pi group, forming glutamine. Glu Glu(c) Overall free-energy change Overall exergonic reaction with energy coupling
    24. 24. Fig. 8-11 Membrane protein) Transport work:TP phosphorylatesansport proteins P Pi Solute Solute transported ADP ATP + Pi Cytoskeletal track (b) Mechanical work: ATP binds non- covalently to motor ATP proteins, then is hydrolyzed Motor protein Protein moved
    25. 25. The Regeneration of ATP• ATP is a renewable resource – ADP + Pi  ATP• The energy to phosphorylate ADP comes from catabolic reactions in the cell (those that release energy)• The chemical potential energy temporarily stored in ATP drives most cellular workCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    26. 26. Fig. 8-12 Energy coupling and the renewal of ATP ATP synthesis ATP hydrolysisrequires energy releases energy (endergonic) (exergonic) ATP + H2O Energy from Energy for cellular catabolism work (endergonic, (exergonic, energy-consumingenergy-releasing ADP + P i processes) processes) Exergonic reactions  drive the formation of ATP (endergonic) Endergonic reactions driven by hydrolysis of ATP (exergonic)
    27. 27. Enzymes speed up metabolic reactions by loweringenergy barriers• A catalyst is a chemical agent that speeds up a reaction without being consumed by the Sucrose reaction• An enzyme is a Sucrase catalytic protein – Ex: Sucrase hydrolyzes sucrose molecules Glucose FructoseCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    28. 28. The Activation Energy Barrier• Every chemical reaction between molecules involves bond breaking and bond forming• Free energy of activation – AKA activation energy (EA) – The initial energy needed to start a chemical reaction – Often supplied in the form of heat from the surroundings – Enzymes decrease EA • Do not affect the change in free energy (∆G) • Hasten reactions that would occur eventuallyCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    29. 29. Fig. 8-14 Energy profile of an exergonic reaction (spontaneous) AB + CD  AC + BD A B Unstable transition state C D A B EA Determines the rate of the rxn Free energy C D Reactants A B ∆G < O C D Products Progress of the reaction
    30. 30. Fig. 8-15 The effect of an enzyme on activation energy Course of reaction EA without enzyme without EA with enzyme enzyme is lower Free energy Reactants Course of ∆G is unaffected reaction by enzyme with enzyme Products Progress of the reaction
    31. 31. Substrate Specificity of Enzymes• The reactant that an enzyme acts on is called the enzyme’s substrate• The enzyme binds to its substrate, forming an enzyme-substrate complex Enzyme + Enzyme-Substrate Enzyme + Substrate(s) complex Product(s)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    32. 32. Fig. 8-16 Induced fit between an enzyme and its substrate Substrate Active site Enzyme Enzyme-substrate complex The active site is the region on the enzyme where the substrate binds. An enzyme’s recognition of a substrate is very specific due to it AA sequence.
    33. 33. Catalysis in the Enzyme’s Active Site• substrate binds to the active site• The active site can lower an EA barrier by – Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrateCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    34. 34. Fig. 8-17 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. Substrates Enzyme-substrate complex 3 Active site can lower EA and speed up a reaction. 6 Active site is available for two new substrate molecules. Enzyme 5 Products are 4 Substrates are released. converted to products. Products
    35. 35. Cofactors• Cofactors are nonprotein enzyme helpers• Cofactors may be inorganic (such as a metal in ionic form) or organic – An organic cofactor is called a coenzyme • Ex: vitaminsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    36. 36. Effects of Local Conditions on Enzyme Activity• An enzyme’s activity can be affected by – pH – Temperature • Each enzyme has an optimal temperature in which it can function • Each enzyme has an optimal pH in which it can function – Chemicals that specifically influence the enzyme • Competitive vs noncompetitive inhibitorsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    37. 37. Fig. 8-18 Optimal temperature for Optimal temperature for typical human enzyme enzyme of thermophilic (heat-tolerant) Rate of reaction bacteria 40 0 60 20 80 100 Temperature (ºC) (a) Optimal temperature for two enzymes Optimal pH for pepsin Optimal pH (stomach enzyme) for trypsin (intestinal Rate of reaction enzyme) 0 41 5 2 3 6 7 8 9 10 pH (b) Optimal pH for two enzymes
    38. 38. Enzyme Inhibitors• Competitive inhibitors bind to the active site of an enzyme, competing with the substrate• Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective• Ex: toxins, poisons, pesticides, and antibioticsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    39. 39. Fig. 8-19 Types of Enzyme Inhibition Substrate Active site Competitive inhibitor Enzyme Noncompetitive inhibitor (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition – The shape of the enzyme is changed
    40. 40. Regulation of enzyme activity helps controlmetabolism• Metabolic pathways are tightly regulated – Allosteric regulation  can inhibit or stimulate an enzyme’s activity – Feedback inhibition  end product of a metabolic pathway shuts down the pathway (ie: negative feedback mechanism) • prevents a cell from wasting chemical resources by synthesizing more product than is neededCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    41. 41. Allosteric Regulation of Enzymes• Enzymes are made up of several subunits or polypeptide chains which have there own active site• Regulatory molecule binds to a protein at one site and affects the protein’s function at another site – Activator  stabilizes the active form of the enzyme – Inhibitor  stabilizes the inactive form of the enzyme• Cooperativity – Can amplify enzyme activity – Binding of a substrate to one active site stabilizes favorable conformational changes at all other subunits – One substrate molecule primes the enzyme to accept additional substrate molecules more readilyCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    42. 42. Allosteric Regulation of Enzymestors and inhibitors (bind to regulatory sites) Allosteric enyzme Active site with four subunits (one of four) (b) Cooperativity Regulatory (substrate binds to active site) site (one of four) Activator Substrate Active form Stabilized active form Oscillation Inactive form Stabilized active form Non- functional Inactive form Inhibitor Stabilized inactive active form site Fig. 8-20
    43. 43. Initial substrate Feedback Active site (threonine) Inhibition available Threonine in active site in isoleucine Enzyme 1 (threonine synthesis Isoleucine used up by deaminase) cell Intermediate A As isoleucine Feedback accumulates, inhibition Enzyme 2 it slows down its Intermediate B own synthesis by allosterically Enzyme 3 inhibiting the enzyme for the first Active site of Intermediate C Isoleucine step of the pathway binds to enzyme 1 no Enzyme 4 allosteric longer binds site threonine; pathway is Intermediate D switched off. Enzyme 5 End product (isoleucine)Fig. 8-22
    44. 44. Practice Quiz1. Lists the three components of ATP.2. ________ reactions release energy while ________ reactions absorb energy3. Cells get energy from __________ to synthesize ATP from ADP and Pi. – Anabolic pathways, catabolic pathways, feedback inhibition, regeneration1. Explain how energy coupling works.2. True of False: ATP hydrolysis is exergonic and spontaneous.3. Enzymes lower the ________ of a chemical reaction.4. True or False: ∆G is decreased when an enzyme is present.5. When a protein is __________ it can become more unstable. Thus the energy from its removal can drive endergonic reactions.6. List the three types of work that ATP does.
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