Microbiology Module 4

  1. Metabolism (Slide 2)
    Sum total of all chemical reactions of the cell

    Energy required to run cellular metabolism is derived from redox reactions

    Energy from redox reactions used to make hi energy phosphate bonds (ATP) and to generate ion gradients (PMF)

    • Fueling rxns include metabolic pathways and processes that allow a cell to accumulate basic molecules needed for growth including:
    • -carbon based precursor metabolites
    • -reducing power in the form of NADH and NADPH
    • -Energy reserve in form of PMF and/or ATP
  2. Overview of metabolic fueling pathways (Slide 3)
    Basic pathways generate 12-13 precursor metabolites, reducing power (NADH/NADPH) and cellular energy (ATP. PMF) needed to make all cellular components

    Respiring micro-orgs use green pathways (aerobic or anaerobic respiration)

    Fermentig microbes use "pink" pathways but also run some rxns from pentose phosphate and TCA (Krebs) cycles
  3. Importance of Redox Reactions (Slide 4)
    The more negative the redox potential ( E knot prime) the higher the energy the electrons have

    Movement of electrons from glc to NAD/NADP generates reducing power

    NADH/NADPH needed for biosynthesis, photosynthesis as well as for providing an initial electron donor for respiration
  4. Glycolysis (Slide 6)
    Common pathway used by most organisms in all domains

    As glc is oxidized e's are trasferred to NAD, liberating energy that is trapped by making hi energy phosphate bonds

    This hi energy P bond is then used to make ATP from ADP (Substrate level Phosphorylation, SLP)

    PEP also contains hi energy bond used to make ATP via SLP
  5. TCA (Krebs or CAC) Cycle (Slide 7)
    Pyruvate from glycolysis is converted to AcetylCoA which enters the cycle

    Fermenting microbes only run the TCA rxns needed to make precursor metabolites, not the whole cycle (A-ketoglutarate used to make all AA's)

    Respiring microbes run whole cycle, generating GTP, NADH and FADH2

    NADH and FADH2 diffuse to respiratory system located on CM
  6. Pentose Phosphate Pathway (Slide 8)
    Interconnect with glycolysis (Shares many intermediates and enzymes with glycolysis)

    Yields 5C sugars necessary for nucleotide synthesis

    Yields NADPH necessary for biosynthesis and photosynthesis

    Provided precursors for aromatic AAs and vitamins
  7. Entner-Doudoroff Pathway (Slide 9)
    • Alternate pathway to glycolysis found in a few microbes
    • (Pseudomonas, enterococcus, and some archaea)

    Yields ATP, NADH and NADPH
  8. Fermentation (Slide 10)
    Usually (not always) carried out under anaerobic condidtions

    Energy only generated via SLPs, not respiration

    H+ tend to accumulate inside cell (use ATP to pump it out of cell). NADH also builds up

    Fermenting microbes must find way to regenerate NAD in order to continue to generate ATP

    Homolactic fermentation is very common. Produces lactic acid and regenarates NAD
  9. Respiration (Slide 12)
    Movement of electrons thru an electron transport chain (ETC). Membrane containing ETC components required to capture and use liberated energy to produce PMF

    Electron carriers arranged on the membrane according to reduction potentials so that electrons move spontaneously generating energy that is extracted in small increments. Carriers MUST touch each other

    Energy liberated is used to pump H+ out of cell and produce PMF

    Aerobic respiration: O2 is final electron acceptor. Anaerobic respiration--cells may use non-O2 final acceptors
  10. Diffusable electron/H carriers used for respiration (Slide 13)
    Each NAD accepts 2 e's and 1 H+. One H+ is released to cytoplasm. FAD accepts 2 e's and 2 H+

    NADH and FADH2 are produced in cytoplasm and diffuse throughout cell, acting as redox cofactors for enzymes and as initial electron donors for respiration
  11. Membrane Bound H and Electron carriers (Slide 14)
    Coenzyme Q (ubiquinone) is common H-carrier. Transfers/accepts 2 e's and 2 H+. Found in CM and can move around CM and lipid bilayer

    Heme is covalently attached to membrane bound cytochromes. Fe is at the core and accepts and transfers 1 electron at a time

    Fe-S proteins in the CM also transfer 1 electron at a time, but not from heme group (Non heme-iron, NHI)
  12. Generation and uses of PMF (Slide 15)
    Electron carriers are positioned next to H carriers on the membrane at some locations

    Energy from spontaneous redx reactions used to take up and then pump H+ out of cell as electrons move between these 2 types of carriers

    PMF is generated and then is used to perform cellular tasks (Make ATP for metabolism and photosynthesis, run flagella, active transport, etc)
  13. Use of PMF to generate ATP (Slide 16)
    ATP synthase (F1F0 ATPase)

    F0 is proton pump--it turns as H+ flow INTO the cell thru the channel and interact with charged residues

    The Gamma (Y) subunit of F1 interacts w/F0 and also turns, synthesizing ATP

    Also works in reverse by fermenters to pump excess H+ out of cell ( using ATP as energy source)
  14. Anaerobic Respiration (Slide 17)
    Variety of final electron acceptors can be used in place of O2

    Include: S, Fe3+, CO2, and NO3

    Greatly extends possible microbial habitat
  15. Anaerobic Vs. Aerobic Respiration in P. Denitrificans (Slide 18)
    Under aerobic conditions e's feed into respiration from NADH or CH3OH and O2 is final electron acceptor

    Under Anaerobic conditions diff. respiratory cmpnts are made and inserted into CM and several diff. final acceptors give rise to NO2-, N2O and N2
  16. Chemolithotrophs (Slide 19)
    Use a variety of Inorganic initial electron donors for respiration. Typically in nutrient deficient environments

    Usually respiration is aerobic, but may be anaerobic

    Reverse respiration can be used to generate NAD(P)H
  17. Generation of PMFs by phototrophs (Slide 20)
    Special molecules (Chlorophyl) absorb light energy and use it to elevate reduction potentials of e's. E's then flow thru an ETC to generate PMF, ATP

    Some microbes contain bacteriorhodopsins (light-driven H+ pumps that directly generate PMFs w/out respiratory chains)
  18. Molecules used in photophosphorylation (Slide 21)
    Chlorophylls (oxygenic photosynthesis) and BChls (non-oxygenic) are inserted in CM with long hydrophobic tails

    Many diff types of Chls/BChls, each absorbing diff. wavelengths of light. All use Mg

    Accessory pigments surround (B)Chls. Also absorb and transfer energy (@ diff. WV) within complexes called reaction centers
  19. CYCLIC photophosphorylation (Slide 22)
    Initial electron donor and final are same (BChl) but electron can be funneled in and out

    Reduction potentials allow flow of electrons to produce PMF

    NAD+ can be reduced and exit the system

    Reverse electron flow in purple bacteria can generate NADH/NADPH

    Systems are anoxygenic and always uses BChls.
  20. NON-CYCLIC photophosphorylation (Slide23)
    2 photosystems are used. Chls are used (oxygenic)

    O2 is produced (1st step) when H2O is used as initial electron donor

    Light is absorbed and transferred to electrons in 2 phases and a PMF is generated

    NADP+ is final electron acceptor, producing NADPH for use in production of carbohydrate
  21. Bacteriorhodopsins (Slide 24)
    Members of rhodopsin superfamily--ALL use light absorbed by retinal

    Light-induced conformational changes in bacteriorhodopsins cause H+ to be pumped out of cells

    Some bacteriorhodopsins act as photoreceptors (absorb light and then cause PMF)
  22. Classification based on O2 utilization (Slide 25)
    During aerobic metabolism reactive oxygen intermediates are formed, including O2 and H2O2

    SOD (superoxide dismutase) converts very toxic superoxide anion into O2 and H2O2 and Catalase/peroxidase converts H2O2 into O2 and H2O

    Microbes contain levels of these enzymes that are proportional to levels of O2 in environment

    • Obligate Aerobe: +SOD and +Catalase
    • Facultative Anaerobe: +SOD and +Catalase
    • Aerotolerant Anaerobe: +SOD and -Catalase
    • Strict Anaerobe: -SOD and -Catalase but +peroxidase
    • Microaerophile: +SOD and +Catalase (Low levels)
Card Set
Microbiology Module 4
Module 4