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Bact. 303 Study Questions III

University of Wisconsin - Madison

Bacterial Metabolism


65. Define anabolism, catabolism and metabolism.

66. Define oxidation and reduction. Describe the crucial role played by coenzymes in biological oxidation-reduction processes.

67. Which of the following substances could serve as energy sources for biological systems: CO2, H2, O2 , Fe+++, NH3, SO4, NO2, NO3, H2S, So, CH4, glucose, Fe++? Which of the foregoing compounds could serve as electron acceptors? Which could serve as either electron donors and electron acceptors?

68. What are the organic electron carriers used in biological systems? Give three examples of electron carriers in electron transport systems and indicate their oxidized and reduced forms. What is the most commonly used soluble electron carrier in cells?

69. What is NAD (NADP)? How does it function in fermentation, respiration and photosynthesis?

70. Describe the role of ATP in energy exchanges within the cell.

71. Distinguish between substrate level phosphorylation and electron transport phosphorylation.

72. What is the relationship between a membrane-bound electron transport system and generation of proton motive force across the membrane which can lead to the synthesis of ATP? What is the role of protons on one side of the membrane and what is the nature and function of membrane-bound ATPase?

73. Differentiate between fermentation and respiration.

74. Write an overall balanced equation starting with glucose which illustrates the following modes of energy-generating metabolism:

  • alcoholic fermentation (yeast)
  • alcoholic fermentation (Zymomonas)
  • homolactic fermentation
  • heterolactic fermentation
  • aerobic respiration

    75. Identify the following terms:

  • Embden-Meyerhof pathway
  • tricarboxylic acid cycle (Kreb's cycle)
  • Electron transport system
  • dEntner-Doudoroff pathway
  • amphibolic pathway

    76. Why is pyruvic acid a key compound in the metabolism of carbohydrates? List several of the end products resulting from bacterial fermentation of glucose and name some important groups of bacteria that form the end products.

    77. How does a respiring heterotrophic bacterium generate a proton motive force? How does a lithotrophic (chemoautotrophic) bacterium generate pmf? How does a photosynthetic bacterium generate pmf? How can this force be used to synthesize ATP? How can fermentative heterotrophic bacteria generate a proton motive force? How can a proton motive force be used directly to do cellular work?

    78. The redox potential (Eo) of a half reaction indicates the tendency of the oxidized (reduced) substance to accept (donate) electrons. Do large positive redox values indicate a great or slight tendency to accept electrons? Do low negative redox values indicate a great or slight tendency to donate electrons?

    79. Describe the flow of electrons in the electron transport system of an aerobic respirer. What are the major classes of coenzymes and enzymes in the respiratory chain?

    80. How many ATP can theoretically be produced from the aerobic respiration of glucose via (a) substrate level phosphorylation and (b) electron transport phosphorylation? What proportion of the total energy available in glucose is captured by the cell?

    81. Compare fermentations to aerobic respiration with respect to (a) the amount of energy released from the energy source (e.g. glucose), (b) the compound that serves as a terminal electron acceptor and (c) the mechanisms of ATP synthesis that are involved.

    82. Much more energy is available from glucose respiration than from glucose fermentation. However, the laws of thermodynamics state that energy is neither created nor destroyed. Where is the energy in the glucose molecules that was not released in the fermenting organism (versus the respiring organism)?

    83. Work through the energy balance sheets for fermentation and respiration and account for all sites of ATP synthesis. Some organisms can obtain about 15 times more ATP when growing aerobically on glucose than anaerobically. What accounts for this difference?

    84. In aerobic respiration, O2 serves as the ultimate electron acceptor. To what substance is O2 always converted as it accepts electrons?

    85. Name four substances that are used by certain bacteria as terminal electron acceptors in the process of anaerobic respiration. How does this process differ from aerobic respiration? What is the biological importance of anaerobic respiration?

    86. Explain why CO2 could not serve as an energy source. Explain why it could serve as an electron acceptor. When CO2 serves as an electron acceptor, to what substance is it often converted?

    87. Define lithotroph (chemoautotroph). List three different compounds that lithotrophs can oxidize as sources of energy. What is the biological importance of lithotrophic metabolism?

    88. In what ways are the hydrogen bacteria, nitrifying bacteria, colorless sulfur bacteria and iron bacteria metabolically similar to those organisms that oxidize carbon compounds aerobically? In what ways are the former different from the latter?

    89. What are the essential biochemical differences between photosynthesis by bacteria and by green plants? What is the molecular nature and the function during the light reaction of photosynthesis of each of these molecules: chlorophyll a, bacteriochlorophyll, cytochromes, quinones, ferredoxin, carotenoids, phycobilins, H20, H2S, NADP, ADP, ATP.

    90. What are the similarities in the processes of electron transport phosphorylation in phototrophic bacteria and respiring bacteria?

    91. What is the Calvin cycle and what is its relationship to autotrophy? What groups of bacteria (in terms of energy generation) are typically autotrophs? What is the key enzyme involved in autotrophic CO2 fixation? What are the alternative mechanisms of CO2 fixation that exist in certain procaryotes?

    92. A bacteriologist has isolated a mutant organism which is blocked in glycolysis between acetaldehyde and ethanol. The organism is no longer able to grow anaerobically on glucose but is still able to grow when O2 is present. Give a possible biochemical explanation for this observation.

    93. A bacteriologist hopes to prevent the growth of obligately-respiratory (non fermentative) pseudomonads by incubating his/her enrichment cultures in the absence of O2. The attempt fails; after incubation the culture is teeming with Pseudomonas species. Give a possible biochemical explanation for this observation.

    94. In an abbreviated diagram of "intermediary metabolism" or biosynthesis, illustrate the relationship of glycolysis and the TCA cycle to the synthesis of macromolecules essential for cell structure and function, metabolism, growth, and reproduction (e.g. cell wall polymers, membranes, nucleic acids, etc.).

    95. Cellulose, the principle component of plant cell walls, is the most abundant organic compound in the world. It is a large molecular weight polymer of glucose. Think about a bacterium in the soil that could utilize cellulose aerobically as a sole source of carbon and energy for growth. Where and how would cellulose utilization begin? What would happen to the carbon in cellulose? What metabolic pathways and mechanisms would the bacterium have?

    96. Are the chemical interactions between small molecules at the active site and the allosteric site of an enzyme similar or different? What are the consequences of binding at the active site versus the allosteric site?

    97. An allosteric protein (enzyme) can be activated or inactivated by binding its respective effector molecule. Explain. Give an example of an allosteric protein which is activated by combining with an effector, and an example of one which is inactivated by combining with an effector. Are allosteric proteins always enzymes?

    98. In bacteria, control of the biochemical pathways of metabolism may be affected at the level of enzyme activity or enzyme synthesis. Explain, using the tryptophan biosynthetic pathway as a model. What specific steps in enzyme (protein) synthesis are susceptible to control mechanisms?

    99. If a biochemical pathway branches leading to the synthesis of two essential metabolites (e.g. amino acids), what characteristic step in the pathway is usually controlled by the process of feedback inhibition?

    100. What control mechanism acts fastest, feedback inhibition or end-product repression?

    101. What is an operon? What are the typical genetic elements of an operon?

    102. Explain the differences in the mechanisms of regulation between (a) inducible versus repressible operons and (b) regulatory proteins that exert positive versus negative control.

    103. What is the function of each of these genetic elements in an inducible biochemical pathway (e.g. the lac operon): regulatory gene, activator, promoter, operator, structural genes, terminator?

    104. What is the function of each of these genetic elements in a repressible biochemical pathway (e.g. the trp operon): promoter, operator, attenuator, structural genes, terminator?

    105. The control processes of end-product repression and attenuation are both effected at the level of transcription. How are the processes fundamentally different, however, and what is the rationale for the existence of both processes to control transcription of the same operon?

    106. What is diauxic growth? Why is there a lag in growth after glucose is exhausted before growth on lactose commences? What is happening during the lag?

    107. What is cyclic AMP and what is its role in the regulation of certain inducible biochemical pathways such as the pathway for lactose utilization?

    108. Why do bacteria have such seemingly elaborate and diverse mechanisms for the control of metabolic processes?



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    Edited with Frontier Applications on a Macintosh on Fri, Mar 14, 1997 at 9:11:04 AM by Kenneth Todar University of Wisconsin-Madison Department of Bacteriology.