Ch. 7 (microbial metabolism)

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  • Prokaryotic Profiles: The Bacteria and Archaea Microbiology: A Systems Approach Chapter 4, pages 80 to 107
  • Answer: D. Noncompetitive inhibition
  • Prokaryotic Profiles: The Bacteria and Archaea Microbiology: A Systems Approach Chapter 4, pages 80 to 107
  • Answer: B. Oxidation
  • Prokaryotic Profiles: The Bacteria and Archaea Microbiology: A Systems Approach Chapter 4, pages 80 to 107
  • Answer: A. 36 – 38 ATP, B. 2 – 36 ATP, C. 2 ATP
  • Prokaryotic Profiles: The Bacteria and Archaea Microbiology: A Systems Approach Chapter 4, pages 80 to 107
  • Answer: B. Amphibolism
  • Ch. 7 (microbial metabolism)

    1. 1. Microbial Metabolism Chapter 7 To run the animations you must be in Slideshow View.Use the buttons on the animation to play, pause, and turnaudio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), youmust first click in the white background before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
    2. 2. Learning Outcomes: Section 7.11. Describe the relationship among metabolism, catabolism, and anabolism.2. Fully define the structure and function of enzymes.3. Differentiate between constitutive and regulated enzymes.4. Diagram some different patterns of metabolism.5. Describe how enzymes are controlled.
    3. 3. Metabolism and the Role of Enzymes•Metabolism: pertains to all chemical reactions and physicalworkings of the cell•Anabolism: -a building and bond-making process that forms larger macromolecules from smaller ones -requires the input of energy (ATP)•Catabolism: -breaks the bonds of larger molecules into smaller molecules -releases energy (used to form ATP)
    4. 4. Simplified Model of Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ANABOLISM Bacterial Glu cell Phe ANABOLISM LysRelative complexity of molecules Ala Macromolecules CATABOLISM Val Glucose ANABOLISM Proteins Building blocks Peptidoglycan Nutrients from Precursor RNA + DNA molecules Amino acids outside Glycolysis Complex lipids or from Sugars internal Pyruvate pathways Krebs cycle Nucleotides Respiratory Acetyl CoA chain Fatty acids Glyceraldehyde-3-P Some assembly Fermentation reactions occur spontaneously Yields energy Uses energy Uses energy Uses energy
    5. 5. Checklist of Enzyme Characteristics
    6. 6. Enzymes: Catalyzing the Chemical Reactions ofLife•Enzymes -are catalysts that increase the rate of chemical reactions without becoming part of the products or being consumed in the reaction -substrates: reactant molecules acted on by an enzyme -Have unique active site on the enzyme that fits only the substrate
    7. 7. Enzyme Structure•Simple enzymes consist of protein alone•Conjugated enzymes contain protein and nonproteinmolecules -sometimes referred to as a holoenzyme -apoenzyme: protein portion of a conjugated enzyme -cofactors: inorganic elements (metal ions) -coenzymes: organic cofactor molecules
    8. 8. Conjugated Enzyme Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coenzyme CoenzymeMetalliccofactor Metallic Apoenzymes cofactor
    9. 9. Enzyme-Substrate Interactions•A temporary enzyme-substrate union must occur at theactive site -fit is so specific that it is described as a “lock- and-key” fit•Bond formed between the substrate and enzyme areweak and easily reversible•Once the enzyme-substrate complex has formed, anappropriate reaction occurs on the substrate, often withthe aid of a cofactor•Product is formed•Enzyme is free to interact with another substrate
    10. 10. Enzyme-Substrate Reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrates Products Enzyme (E) ES complex E Does not fit(a) (b) (c)
    11. 11. How Enzymes WorkPlease note that due to differingoperating systems, some animationswill not appear until the presentation isviewed in Presentation Mode (SlideShow view). You may see blank slidesin the “Normal” or “Slide Sorter” views.All animations will appear after viewingin Presentation Mode and playing eachanimation. Most animations will requirethe latest version of the Flash Player,which is available athttp://get.adobe.com/flashplayer.
    12. 12. Cofactors: Supporting the Work of Enzymes•The need of microorganisms for trace elements arisesfrom their roles as cofactors for enzymes -iron, copper, magnesium, manganese, zinc, cobalt, selenium, etc.•Participate in precise functions between the enzymeand substrate -help bring the active site and substrate close together -participate directly in chemical reactions with the enzyme-substrate complex
    13. 13. Cofactors: Supporting the Work of Enzymes(cont’d)•Coenzymes -organic compounds that work in conjunction with an apoenzyme -general function is to remove a chemical group from one substrate molecule and add it to another substrate molecule -carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups -many derived from vitamins
    14. 14. Classification of Enzyme Functions•Enzymes are classified and named according tocharacteristics such as site of action, type of action, andsubstrate -prefix or stem word derived from a certain characteristic, usually the substrate acted upon or type of reaction catalyzed -ending –ase
    15. 15. Classification of Enzyme Functions (cont’d)•Six classes of enzymes based on general biochemicalreaction -oxidoreductases: transfer electrons from one substrate to another, dehydrogenases transfer a hydrogen from one compound to another -transferases: transfer functional groups from one substrate to another -hydrolases: cleave bonds on molecules with the addition of water
    16. 16. Classification of Enzyme Functions (cont’d)•Six classes of enzymes based on general biochemicalreaction (cont’d) -lyases: add groups to or remove groups from double-bonded substrates -isomerases: change a substrate into its isomeric form -ligases: catalyze the formation of bonds with the input of ATP and the removal of water
    17. 17. Classification of Enzyme Functions (cont’d)•Each enzyme also assigned a common name thatindicates the specific reaction it catalyzes -carbohydrase: digests a carbohydrate substrate -amylase: acts on starch -maltase: digests maltose -proteinase, protease, peptidase: hydrolyzes the peptide bonds of a protein -lipase: digests fats -deoxyribonuclease (DNase): digests DNA -synthetase or polymerase: bonds many small molecules together
    18. 18. Regulation of Enzyme Function•Constitutive enzymes: always present in relatively constant amounts regardless ofthe amount of substrate•Regulated enzymes: production is turned on (induced) or turned off (repressed) inresponses to changes in concentration of the substrate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Constitutive Enzymes Regulated Enzymes Add more substrate. Add more substrate. Enzyme is induced. No change in or (a) amount of enzyme. Remove substrate. (b) Enzyme is repressed.
    19. 19. Regulation of Enzyme Function (cont’d)•Activity of enzymes influenced by the cell’senvironment -natural temperature, pH, osmotic pressure -changes in the normal conditions causes enzymes to be unstable or labile•Denaturation -weak bonds that maintain the native shape of the apoenzyme are broken -this causes disruption of the enzyme’s shape -prevents the substrate from attaching to the active site
    20. 20. Metabolic Pathways•Often occur in a multistep series or pathway, with eachstep catalyzed by an enzyme•Product of one reaction is often the reactant(substrate) for the next, forming a linear chain orreaction•Many pathways have branches that provide alternatemethods for nutrient processing•Others have a cyclic form, in which the startingmolecule is regenerated to initiate another turn of thecycle•Do not stand alone; interconnected and merge at manysites
    21. 21. Patterns of Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Multienzyme Systems Linear Cyclic Branched Divergent Convergent A M A X U B V T input N B Y C S product Z Krebs W O P Cycle C Z D Y X O1 Q M Example: E Amino acid synthesis O2 R NExample:Glycolysis
    22. 22. Biochemical PathwayPlease note that due to differingoperating systems, some animationswill not appear until the presentation isviewed in Presentation Mode (SlideShow view). You may see blank slidesin the “Normal” or “Slide Sorter” views.All animations will appear after viewingin Presentation Mode and playing eachanimation. Most animations will requirethe latest version of the Flash Player,which is available athttp://get.adobe.com/flashplayer.
    23. 23. Direct Controls on the Action of Enzymes•Competitive inhibition -inhibits enzyme activity by supplying a molecule that resembles the enzyme’s normal substrate -“mimic” occupies the active site, preventing the actual substrate from binding•Noncompetitive inhibition -enzymes have two binding sites: the active site and a regulatory site -molecules bind to the regulatory site -slows down enzymatic activity once a certain concentration of product is reached
    24. 24. Two Common Control Mechanisms for Enzymes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Competitive Inhibition Noncompetitive Inhibition Normal Competitive Substrate substrate inhibitor with similar shape Active site Both molecules compete for the active site. Enzyme Enzyme Regulatory site Regulatory molecule (product) Reaction proceeds. Reaction is blocked Reaction proceeds. Reaction is blocked because because competitive binding of regulatory molecule inhibitor is incapable in regulatory site changes of becoming a product. conformation of active site so Product that substrate cannot enter.
    25. 25. Controls on Enzyme Synthesis•Enzymes do not last indefinitely; some wear out, someare degraded deliberately, and some are diluted witheach cell division•Replacement of enzymes can be regulated according tocell demand•Enzyme repression: genetic apparatus responsible forreplacing enzymes is repressed -response time is longer than for feedback inhibition•Enzyme induction: enzymes appear (are induced) onlywhen suitable substrates are present
    26. 26. Enzyme Repression Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 DNA transcribed into RNA 2 RNA translated into protein 3 Protein6 Excess product binds to DNA and shuts down 7 further enzyme production. DNA can not be transcribed; the protein cannot be made. 4 Folds to form functional enzyme structure 5 Substrate = + Products Substrate Enzyme
    27. 27. Enzyme Induction in E. coli•If E. coli is inoculated into a medium containing onlylactose, it will produce the enzyme lactase to hydrolyzeit into glucose and galactose•If E. coli is subsequently inoculated into a mediumcontaining only sucrose, it will cease to synthesizinglactase and begin synthesizing sucrase•Allows the organism to utilize a variety of nutrients,and prevents it from wasting energy by making enzymesfor which no substrates are present
    28. 28. Concept CheckWhich of the following mechanisms of enzyme controlblocks a reaction catalyzed by an enzyme, by the bindingof a product to a regulatory site on the enzyme? A. enzyme repression B. competitive inhibition C. enzyme induction D. noncompetitive inhibition E. None of the choices is correct.
    29. 29. Learning Outcomes: Section 7.26. Name the chemical in which energy is stored in cells.7. Create a general diagram of a redox reaction.8. Identify electron carriers used by cells.
    30. 30. Energy in Cells•Energy is managed in the form of chemical reactionsthat involve the making and breaking of bonds and thetransfer of electrons•Exergonic reactions release energy, making it availablefor cellular work•Endergonic reactions are driven forward with theaddition of energy•Exergonic and endergonic reactions are often coupledso that released energy is immediately put to work
    31. 31. Oxidation and Reduction•Oxidation: loss of electrons -when a compound loses electrons, it is oxidized•Reduction: gain of electrons -when a compound gains electrons, it is reduced•Oxidation-reduction (redox) reactions are common inthe cell and are indispensable to the required energytransformations
    32. 32. Oxidation and Reduction (cont’d)•Oxidoreductases: enzymes that remove electronsfrom one substrate and add them to another -their coenzyme carriers are nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD)•Redox pair: an electron donor and an electron acceptorinvolved in a redox reaction
    33. 33. Redox PairsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na 2 8 1 Cl 287 Reducing agent Oxidizing agent gives up electrons. accepts electrons. + - Na 2 8 Cl 288 Oxidized Reduced cation anion
    34. 34. Oxidation and Reduction (cont’d)•Energy present in the electron acceptor can becaptured to phosphorylate (add an inorganicphosphate) to ADP or to some other compound to storeenergy in ATP•The cell does not handle electrons as discrete entitiesbut rather as parts of an atom such as hydrogen(consisting of a single electron and a single proton)•Dehydrogenation: the removal of hydrogen during aredox reaction
    35. 35. Electron Carriers: Molecular Shuttles•Electron carriers resemble shuttles that are alternately loaded and unloaded,repeatedly accepting and releasing electrons and hydrogens to facilitate transfer ofredox energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NAD+ NAD H + H+ From substrate Oxidized Nicotinamide Reduced Nicotinamide H H H H+ C 2H C C C C NH2 C C C NH2 2e: C C O C C O N N Adenine P Ribose P P P
    36. 36. ATP: Metabolic Money•Three-part molecule -nitrogen base (adenine) Adenosine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenosine Triphosphate Diphosphate Adenosine (ATP) (ADP) -5-carbon sugar (ribose) H H Adenine N -chain of three phosphate N N H groups bonded to ribose H N N -phosphate groups are OH OH OH H bulky and carry negative HO P O P O P O H charges, causing a strain O O O O between the last two H H H H phosphates Bond that releases energy when broken OH OH Ribose -the removal of the terminal phosphate releases energy
    37. 37. Concept CheckIn a redox reaction, loss of electrons is A. phosphorylation. B. oxidation. C. fermentation. D. reduction. E. None of the choices is correct.
    38. 38. Learning Outcomes: Section 7.39. Name three basic catabolic pathways, and give an estimate of how much ATP each of them yields.10. Write a summary statement describing glycolysis.11. Describe the Krebs cycle.12. Discuss the significance of the electron transport system.13. Point out how anaerobic respiration differs from aerobic respiration.14. Provide a summary of fermentation.15. Describe how noncarbohydrate compounds are catabolized.
    39. 39. Catabolism•Metabolism uses enzymes to catabolize organicmolecules to precursor molecules that cells then use toanabolize larger, more complex molecules•Reducing power: electrons available in NADH andFADH2•Energy: stored in the bonds of ATP -both are needed in large quantities for anabolic metabolism -both are produced during catabolism
    40. 40. How the NAD+ WorksPlease note that due to differingoperating systems, some animationswill not appear until the presentation isviewed in Presentation Mode (SlideShow view). You may see blank slidesin the “Normal” or “Slide Sorter” views.All animations will appear after viewingin Presentation Mode and playing eachanimation. Most animations will requirethe latest version of the Flash Player,which is available athttp://get.adobe.com/flashplayer.
    41. 41. Overview of the Three Main Catabolic Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. AEROBIC RESPIRATION ANAEROBIC RESPIRATION FERMENTATION Glycolysis Glycolysis Glycolysis NAD H NAD H NAD H CO2 CO2 CO2Yields 2 ATPs ATP ATP ATP NAD H Krebs NAD H Krebs Cycle CO2 Cycle CO2 FADH2 FADH2Yields 2 GTPs ATP ATP Fermentation Electron Transport System Electron Transport System Using organic compounds as Using O2 as electron acceptor Using non- O2 compound as electron acceptor electron acceptor (So42–, NO3–, CO32–)Yields variableamount ofenergy ATP ATP Alcohols, acidsMaximum net yield 36–38 ATPs 2–36 ATPs 2 ATPs
    42. 42. Getting Materials and Energy•Nutrient processing in bacteria is extremely varied, butin most cases the nutrient is glucose•Aerobic respiration -a series of reactions that converts glucose to CO2 and allows the cell to recover significant amounts of energy -utilizes glycolysis, the Krebs cycle, and the electron transport chain -relies on free oxygen as the final electron and hydrogen acceptor -characteristic of many bacteria, fungi, protozoa,
    43. 43. Getting Materials and Energy (cont’d)•Anaerobic respiration -used by strictly anaerobic organisms and those who are able to metabolize with or without oxygen -involves glycolysis, the Krebs cycle, and the electron transport chain -uses NO3-, SO42-, CO33-, and other oxidized compounds as final electron acceptors•Fermentation -incomplete oxidation of glucose -oxygen is not required -organic compounds are final electron acceptors
    44. 44. Glycolysis•Turns glucose into pyruvate, which yields energy in the pathways thatfollow Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 7.2 Glycolysis Energy Lost or Gained Overview Details Glucose Uses 2 ATPs C C C C C C Three reactions alter and rearrange the 6-C glucose molecule into 6-C fructose-1,6 diphosphate. Fructose-1, 6-diphosphate C C C C C C One reaction breaks fructose-1,6-diphosphate into two 3-carbon molecules. C C C C C C Yields 4 ATPs and 2 NADHs Pyruvate Pyruvate Five reactions convert each 3 carbon molecule into the 3C pyruvate. C C C C C C Total Energy Yield: 2 ATPs and Pyruvate is a molecule that is uniquely suited for chemical 2 NADHs reactions that will produce reducing power (which will eventually produce ATP).
    45. 45. How Glycolysis WorksPlease note that due to differingoperating systems, some animationswill not appear until the presentation isviewed in Presentation Mode (SlideShow view). You may see blank slidesin the “Normal” or “Slide Sorter” views.All animations will appear after viewingin Presentation Mode and playing eachanimation. Most animations will requirethe latest version of the Flash Player,which is available athttp://get.adobe.com/flashplayer.
    46. 46. The Krebs Cycle (Citric Acid Cycle):A Carbon and Energy Wheel•After glycolysis, pyruvic acid is still energy-rich•cytoplasm of bacteria and mitochondrial matrix of eukaryotes -a cyclical metabolic pathway that begins with acetyl CoA, which joins with oxaloacetic acid, and then participates in seven other additional transformations -transfers the energy stored in acetyl CoA to NAD+ and FAD by reducing them (transferring hydrogen ions to them) -NADH and FADH2 carry electrons to the electron transport chain -2 ATPs are produced for each molecule of glucose through phosphorylation
    47. 47. The Krebs Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Table 7.3 The Krebs CycleEnergy Lost or Gained Overview DetailsOne CO2 is liberated and one NADH is The 3C pyruvate is converted toformed. 2C acetyl CoA in one reaction. Pyruvate Pyruvate C C C C C C Remember: This happens twice forEach acetyl CoA yields 1 GTP, 3 NADHs, Acetyl CoA each glucose In the first reaction, acetyl CoA1 FADH, and 2 CO2 molecules. molecule that donates 2Cs to the 4C molecule Oxaloacetate C C enters glycolysis. oxaloacetate to form 6C citrate.Total Yield per 2 acetyl CoAs: C C C CCO2: 4 Citrate In the course of seven more Yields: reactions, citrate is manipulated Energy: 2 GTPs, 6 NADHs, 2 FADHs 3 NADHs C C C C C C to yield energy and CO2 and 1 FADH2 oxaloacetate is regenerated. CO2 CO2 Intermediate molecules on the wheel can be shunted into other Other metabolic pathways as well. intermediates GTP
    48. 48. How the Krebs Cycle Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
    49. 49. The Respiratory Chain:Electron Transport•A chain of special redox carriers that receives reducedcarriers (NADH, FADH2) generated by glycolysis and theKrebs cycle -passes them in a sequential and orderly fashion from one to the next -highly energetic -allows the transport of hydrogen ions outside of the membrane -in the final step of the process, oxygen accepts electrons and hydrogen, forming water
    50. 50. The Respiratory Chain:Electron Transport (cont’d)•Principal compounds in the electron transport chain: -NADH dehydrogenase -flavoproteins -coenzyme Q (ubiquinone) -cytochromes•Cytochromes contain a tightly bound metal ion in theircenter that is actively involved in accepting electronsand donating them to the next carrier in the series
    51. 51. The Respiratory (Electron Transport) Chain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 7.4 The Respiratory (Electron Transport) Chain Reduced carriers (NADH, FADH) transfer electrons and H+ to first electron carrier in chain: NADH dehydrogenase. These are then sequentially transferred to the next four to six carriers with progressively more positive reduction potentials. The carriers are called cytochromes. The number of carriers varies, depending on the bacterium. Simultaneous with the reduction of the electron carriers, protons are moved to the outside of the membrane, creating a concentration gradient (more protons outside than inside the cell). The extracellular space becomes more positively charged and more acidic than the intracellular space. This condition H+ creates the proton motive force, by which protons flow down the H+ concentration gradient through the ATP synthase embedded in the H+ membrane. This results in the conversion of ADP to ATP. H+ ATP H+ synthaseCell wall H+ H+ H+ ADP ATP H+ H+Cell H+ H+ Once inside the cytoplasm, protons combine with O2 tomembrane H+ form water (in aerobic respirers [left]), and with a variety ofWith ETS Cytochromes H+ H+ O-containing compounds to produce more reduced compounds. NAD H O2 SO42– NO3– Aerobic respiration yields a maximum of 3 ATPs per oxidized NADH and 2 ATPs per oxidized FADH. H2 O NO2– HS– Cytoplasm Anaerobic respiration yields less per NADH and FADH. Aerobic Anaerobic respirers respirers
    52. 52. The Electron Transport Chain (cont’d)•Electron transport carriers and enzymes are embedded in the cellmembrane in prokaryotes and on the inner mitochondrial membrane ineukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane H+ ions space Cristae
    53. 53. The Electron Chain (cont’d)•Released energy from electron carriers in the electrontransport chain is channeled through ATP synthase•Oxidative phosphorylation: the coupling of ATPsynthesis to electron transport -each NADH that enters the electron transport chain can give rise to 3 ATPs -Electrons from FADH2 enter the electron transport chain at a later point and have less energy to release, so only 2 ATPs result
    54. 54. The Terminal Step•Aerobic respiration -catalyzed by cytochrome aa3, also known as cytochrome oxidase -adapted to receive electrons from cytochrome c, pick up hydrogens from solution, and react with oxygen to form water 2H+ + 2e- + ½ O2  H20
    55. 55. The Terminal Step (cont’d)•Most eukaryotes have a fully functioning cytochromesystem•Bacteria exhibit wide-ranging variations in this system -some lack one or more redox steps -several have alternative electron transport schemes -lack of cytochrome c oxidase is useful in differentiating among certain genera of bacteria
    56. 56. The Terminal Step (cont’d)•A potential side reaction of the respiratory chain is theincomplete reduction of oxygen to the superoxide ion(O2-) and hydrogen peroxide (H2O2)•Aerobes produce enzymes to deal with these toxicoxygen products -superoxide dismutase -catalase -Streptococcus lacks these enzymes but still grows well in oxygen due to the production of peroxidase
    57. 57. Electron Transport System and ATP Synthesis Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
    58. 58. The Terminal Step (cont’d)•Anaerobic Respiration -the terminal step utilizes oxygen-containing ions, rather than free oxygen, as the final electron acceptor Nitrate reductase NO3- + NADH NO2- + H2O + NAD+•Nitrate reductase catalyzes the removal of oxygen fromnitrate, leaving nitrite and water as products
    59. 59. Anaerobic Respiration (cont’d)•Denitrification -some species of Pseudomonas and Bacillus possess enzymes that can further reduce nitrite to nitric oxide (NO), nitrous oxide (N2O), and even nitrogen gas (N2) -important step in recycling nitrogen in the biosphere•Other oxygen-containing nutrients reducedanaerobically by various bacteria are carbonates andsulfates•None of the anaerobic pathways produce as much ATPas aerobic respiration
    60. 60. After Pyruvic Acid II: Fermentation•Fermentation -the incomplete oxidation of glucose or other carbohydrates in the absence of oxygen -uses organic compounds as the terminal electron acceptors -yields a small amount of ATP -used by organisms that do not have an electron transport chain -other organisms revert to fermentation when oxygen is lacking
    61. 61. Fermentation (cont’d)•Only yields 2 ATPs per molecule of glucose•Many bacteria grow as fast as they would in thepresence of oxygen due to an increase in the rate ofglycolysis•Permits independence from molecular oxygen -allows colonization of anaerobic environments -enables adaptation to variations in oxygen availability -provides a means for growth when oxygen levels are too low for aerobic respiration
    62. 62. Fermentation (cont’d)•Bacteria and ruminant cattle -digest cellulose through fermentation -hydrolyze cellulose to glucose -ferment glucose to organic acids which are absorbed as the bovine’s principal energy source•Human muscle cells -undergo a form of fermentation that permits short periods of activity after the oxygen supply has been depleted -convert pyruvic acid to lactic acid, allowing anaerobic production of ATP -accumulated lactic acid causes muscle fatigue
    63. 63. Fermentation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Table 7.5 Fermentation C C C Pyruvic acid from glycolysis can itself become the electron acceptor. Pyruvic acid CO2 Remember: This happens twice for H each glucose Pyruvic acid can also be enzymatically altered and then serve as molecule that H C C H the electron acceptor. enters glycolysis. H O The NADs are recycled to reenter glycolysis. Acetaldehyde NAD H NAD H The organic molecules that became reduced in their role as electron acceptors are extremely varied, and often yield useful H H H OH products such as ethyl alcohol, lactic acid, propionic acid, O butanol, and others. NAD + H C C OH H C C C OH H H H H Ethyl alcohol Lactic acid
    64. 64. Products of Fermentation in Microorganisms•Alcoholic beverages: ethanol and CO2•Solvents: acetone, butanol•Organic acids: lactic acid, acetic acid•Vitamins, antibiotics, and hormones•Large-scale industrial syntheses by microorganismsoften utilize entirely different fermentation mechanismsfor the production of antibiotics, hormones, vitamins,and amino acids
    65. 65. Catabolism of Noncarbohydrate Compounds•Complex polysaccharides broken into componentsugars, which can enter glycolysis•Lipids broken down by lipases -glycerol converted to dihydroxyacetone phosphate, which can enter midway into glycolysis -fatty acids undergo beta oxidation, whose products can enter the Krebs cycle as acetyl CoA
    66. 66. Catabolism of Noncarbohydrate Compounds(cont’d)•Proteins are broken down into amino acids byproteases -amino groups are removed through deamination -remaining carbon compounds are converted into Krebs cycle intermediates or decarboxylated
    67. 67. Concept CheckWhat is the maximum net yield of ATP per molecule ofglucose for each of the following types of respiration? A. aerobic respiration B. anaerobic respiration C. fermentation
    68. 68. Learning Outcomes: Section 7.416. Provide an overview of the anabolic stages of metabolism.17. Define amphibolism.
    69. 69. Anabolism and the Crossing Pathways ofMetabolism•The Frugality of the Cell -cells have systems for careful management of carbon compounds -catabolic pathways contain strategic molecular intermediates (metabolites) that can be diverted into anabolic pathways -a given molecule can serve multiple purposes; maximum benefit can be derived from all nutrients and metabolites of the cell pool•Amphibolism: the ability of a system to integratecatabolic and anabolic pathways to improve cellefficiency
    70. 70. Amphibolic Pathways of Glucose Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Table 7.6 Amphibolic Pathways of Glucose MetabolismAnabolic PathwaysIntermediates from glycolysis are fed into the aminoacid synthesis pathway. From there, the compounds are Enzymes/ Cell wall Membranes Cell Chromosomes Membranes storage storage structureformed into proteins. Amino acids can then contributenitrogenous groups to nucleotides to form nucleic acids.Glucose and related simple sugars are made into Nucleic Starch/ Lipids/ Macromolecule ANABOLISM Proteinsadditional sugars and polymerized to form complex acids Cellulose Fatscarbohydrates.The glycolysis product acetyl CoA can be oxidized to form Nucleotides Amino acids Carbohydrates Fatty acids Building blockfatty acids, critical components of lipids.Catabolic Pathways Deamination Beta oxidation CATABOLISMIn addition to the respiration and fermentation pathwaysalready described, bacteria can deaminate amino acids, GLUCOSEwhich leads to the formation of a variety of metabolicintermediates, including pyruvate and acetyl CoA.Also, fatty acids can be oxidized to form acetyl CoA. Glycolysis Metabolic pathways Pyruvic acid Acetyl coenzymeA Simple pathways Krebs Cycle CO2 NH3 H2 O
    71. 71. Anabolism:Formation of Macromolecules•Two possible sources for monosaccharides, aminoacids, fatty acids, nitrogenous bases, and vitamins -enter the cell from the outside as nutrients -can be synthesized through various cellular pathways
    72. 72. Anabolism:Formation of Macromolecules (cont’d)•The degree to which an organism can synthesize itsown building blocks is genetically determined and variesfrom group to group -autotrophs only require CO2 as a carbon source and a few minerals to synthesize all cell substances -some heterotrophs such as E. coli can synthesize all cellular substances from a few minerals and one organic carbon source such as glucose
    73. 73. Carbohydrate Biosynthesis•Glucose has a crucial role in bioenergetics -major component of cellulose cell walls and certain storage molecules -an intermediary in glycolysis, glucose-6-P is used to form glycogen -peptidoglycan is a linked polymer derived from fructose-6-P from glycolysis -the carbohydrates ribose and deoxyribose are essential building blocks of nucleic acids -polysaccharides are the predominant components of capsules and glycocalyx
    74. 74. Amino Acids, Protein Synthesis, and NucleicAcid Synthesis•Proteins -account for a large proportion of a cell’s constituents -essential components of enzymes, cell membrane, cell wall, and cell appendages -20 amino acids needed to make these proteins -some organisms, such as E. coli, have pathways that will synthesize all 20 amino acids -others, such as animals, lack some or all of the pathways for amino acid synthesis
    75. 75. Amino Acids, Protein Synthesis, and NucleicAcid Synthesis (cont’d)•Nucleic acids: DNA and RNA -responsible for the hereditary continuity of cells and the direction of protein synthesis -covered in more detail in chapter 8
    76. 76. Assembly of the Cell•Component parts of bacteria are being synthesized on acontinuous basis•Catabolism is also taking place as long as nutrients arepresent and the cell is nondormant•Cell division takes place when -anabolism produces enough macromolecules to serve two cells -DNA replication produces duplicate copies of the cell’s genetic material -membrane and cell wall have increased in size•Catabolic processes provide all of the energy for complexbuilding reactions
    77. 77. Concept CheckThe ability of a cell to integrate molecule-using andmolecule-building pathways to improve cell efficiency isknown as A. anabolism. B. amphibolism. C. catabolism. D. metabolism. E. None of the choices is correct.

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