Microbial_Metabolism by ashrafp


									                                        BISC 115 - Human Microbiology

Lecture:       Microbial Metabolism

Reading:       pp. 27-58, 219-254


1. Distinguish between catabolic and anabolic reactions.

2. Describe the types of compounds that serve as electron donors and those that may serve as electron
acceptors in catabolic reactions. Differentiate between fermentation and respiration in terms of electron

3. Discuss the Embden-Meyerhof-Parnas pathway, the TCA cycle and the electron transport system in general
terms, emphasizing the metabolic functions of each. Distinguish between substrate-level phosphorylation and
electron-transport phosphorylation (oxidative phosphorylation).

Outline of Lecture:

 I. Overview of Metabolism - sum of biochemical reactions that occur within a cell

       A. General Comparison of Catabolic and Anabolic Reactions

       1. Catabolic (“Glycolysis”)

                Breaking down carbohydrate, lipids, proteins into smaller units to get energy
                    a. degradative reactions
                    b. generate energy
                             release energy in the form of ATP
                    c. oxidation reactions (release H+ and e-)
                             Oxidizing these compounds using a coenzyme NAD+ to get smaller products
                                like CO2 and H2O

               2. Anabolic
                      a. biosynthetic reactions
                                Use simple sugar & amino acid to get carbohydrate & protein
                      b. utilize energy
                                Requires ATP
                                use these energy from Glycolysis to carry on biosynthetic (anabolic)
                                   pathways to make the bigger structure
                      c. reduction reactions (gain H+ and e-)

       B. Oxidation-Reduction Reactions

               1. Oxidation - removal of electrons

               2. Reduction - gain of electrons

       C. Characteristics of Catabolic Reactions

               1. Biological systems (e.g. glycolysis- oxidation of glucose, release of energy ATP)
                   Oxidizing organic compounds, chemoheterotrophs.

             When you lose an electron (dehydrogenation rxn) you also lose a proton along the way
             Methane- reduced; Carbon dioxide- oxidized
              a. complete oxidation
                     i. Removing electron and proton from glucose, common pathway in most
                        bacteria, oxidize glucose to get ATP
                    ii. Not all bacteria can completely oxidize glucose

              C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O

              b. role of coenzymes
                       i. fits into enzyme, remove chemical group from that substrate and transfer it to
                          something else
                      ii. work in concert with enzymes
                     iii. NAD+- coenzyme that remove from electron and proton from a reduced
                          substrate and carry it somewhere else

      2. Electron donor versus electron acceptor

      3. Final electron acceptor

              a. organic molecule (fermentation)

              b. inorganic molecule (respiration)

                     (1) molecular oxygen (aerobic respiration)

                     (2) inorganic molecule other than oxygen (anaerobic respiration)- does not like

D. Examples of Catabolic Pathways

      1. Glycolysis- requires ATP
              Start off with 6-carbon sugar, adds phosphate groups on both ends of glucose, so
                 you end up with 2 “3-carbon units”, each of which has a phosphate group on it
              Each of those 3-carbon units will become phosphorylated again.
              1 Glucose = 4 ATP, but 2 ATP was required to start, so it leaves 2 left
              Have reduced NADH, but need oxidize NAD to keep glycolysis going, finite amount
                 of NAD in the cell, so pick up electron and proton takes them somewhere, and repeat
                 this process, this process varies btwn bacteria

              a. Embden-Meyerhof-Parnas pathway

              b. substrate-level phosphorylation
                  Production of ATP, phosphate that adds to ADP comes from a substrate, glucose

      2. Fermentations
            a. performed by anaerobes and facultative anaerobes in absence of O2

              b. permit overall oxidation-reduction balance (NADH2 --> NAD)
                   i.   permits regeneration of reduced NADH to oxidize NAD, go back into

              c. pyruvate usual electron acceptor

              i.      end product of glucose, pick up proton and electron from NAD to make
                      different products

       d. specific fermentations for specific groups or species

       - broke glucose into pyruvate, reduced NADH along the way, oxidize it back into NAD
       and dumps those electron and proton on pyruvate to form lactic acid (organic
       compound), occurs in human muscle

3. Aerobic respiration

       a. performed by aerobes, microaerophiles, and facultative anaerobes in presence of

       b. tricarboxylic acid (TCA) cycle (Kreb's cycle, citric acid cycle)

                   (1) reactions
                          a. breakdown pyruvate (3-carbon sugar) even further to get energy
                          b. get even more reduce NADH; the 3-carbons are released as carbon
                              dioxide and a coenzyme FAD is also reduced
                          c. make GTP (~ ATP)
                          d. Overall, more energy, a lot of reduced coenzyme and generate CO2

                   (2) products

                          (a) 6 CO2/2 pyruvate
                          (b) 2 GTP/2 pyruvate
                          (c) 8 NADH2/2 pyruvate
                          (d) 2 FADH2/2 pyruvate

       c. electron transport system- found in the mitochondria
              i. in bacteria, its found in their cell membrane since they do not have a

                   (1) role of NADH2 and FADH2

                   (2) components of electron transport chain
                   - reoxides NADH2 and FADH2

                          (a) flavoproteins

                          (b) quinones

                          (c) cytochromes

                   (3) oxidative phosphorylation (electron transport phosphorylation)
                       o Throught the components of the electron transport chain, this process
                           oxidize NAD & FAD

                   (4) chemiosmotic theory: Fig 8.23

       Glycolyisis: Bacteria vs. Humans
           Occurs in the cytoplasm of both human and bacterial cells

                            Converting a 6-carbon sugar of glucose to 2, 3- carbon pyruvate, and we make
                             ATP via substrate-level phosphorylation and reduce some NAD
                            If aerobically, pyruvate goes into TCA cycle and generate some CO2 and ATP,
                             and reduce some NAD and FAD, occurs in cytoplasm of bacteria and in
                             mitochondria of humans
                            Electron transport chain- mitochondria: humans; cytoplasm: bacteria

                     d. products (glycolysis and aerobic respiration):

                     6 CO2 + 6 H2O + 38 ATP / 1 glucose

                            Generally produce 40 ATP, but 2 is needed for things to get going (38 ATP per
                            Fermentative growth would be much slower since less production of ATP
                             compared to aerobes

             4. Anaerobic respiration

                     a. performed by anaerobes and facultative anaerobes in absence of O2

                     b. final electron acceptor an inorganic molecule other than O2 (an
                     oxygen-containing salt like NO3-, SO4-2, CO3-3)

                     c. TCA cycle and similar electron transport system used

                     d. usually generates <38 ATP/glucose
                            i. gets more than fermentation, but less than aerobic

II.   Anabolic Reactions: Biosynthesis of precursor molecules (amino acids, carbohydrates, fatty acids,
      organic bases) used to provide the cell with specific polymers needed for growth and reproduction
      (proteins, polysaccharides, lipids, nucleic acids, etc.) Fig. 8.27
       a. utilize the things bacteria break down from catabolism to rebuild important structures in the cell

      b. Amphibolic pathways- serve in both catabolism and anabolism (biosynthesis)

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