Chapter 5a by n3NYd0M

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									CHAPTER 5

 MICROBIAL
METABOLISM
• Energy
  – Chemical work
  – Transport work
  – Mechanical work


• Laws of thermodynamics
  – 1st
  – 2nd – entropy
• Two fundamental tasks required for growth
  and reproduction
  – Catabolism

  – Anabolism
• Metabolism
  – Amazing diversity but also unity
     • Ordered, enzyme-mediated pathways
     • ATP
     • Redox
• Catabolic reactions
  – hydrolytic, exergonic (-ΔG)
  – Keq>1, spontaneous
  – Cellular respiration
     • Provides precursor molecules and energy for anabolic
       reactions
• Anabolic reactions
  – dehydration synthesis, endergonic (+ΔG)
  – Keq<1, not favorable
  – protein synthesis
    • Consumes energy and precursor molecules in the
      biosynthesis of macromolecules
Amphibolic reactions
• Activation energy
•
• Reaction rate influenced by:
  – Temperature

  – Concentration

  – Enzymes – biological catalysts
• Enzymes:
• All protein or holoenzymes
  – Apoenzyme + Cofactor
  – Prosthetic group or coenzyme
• Characteristics of enzymes
  – do not make reactions happen that could not
    happen on their own
  – not permanently altered or used up
  – substrate-specific
  – Function is based on structure
• Six functional categories of enzymes:
      Unconventional Enzymes

• Ribozymes
  – Novel type of RNA
• Extremozymes
  – Have molecular applications
         Mechanism of Enzymatic Action




Lock and Key or Induced Fit
Regulated through through reversible covalent modification and allosteric
effectors
  Factors influencing enzyme activity

• Temperature, ph, UV
  radiation, chemicals
• substrate
  concentration
• competitive inhibition
• Non-competitive
  (allosteric) inhibition
Michaelis Constant (Km)
Feedback Inhibition
  •Negative allosteric effector
  •Isozymes may still function
    Oxidation-Reduction Reactions
• Redox reactions liberate energy
  – always coupled
  – oxidation (electron donor)
  – reduction (electron acceptor)


• Standard reduction potential (E`O)

• Reducing power (potential energy)
Reduction of NAD – common electron carrier




  •Electrons and protons are typically removed together
     •The equivalent of a hydrogen atom
NAD and
FAD are
common
electron
carriers
E’0 of various biologically
important redox couples


Electrons moving toward
less negative acceptors
release free energy


Amount of energy released
correlates with magnitude
of difference in E’0
               ATP Synthesis
•   Free energy used to phosphorylate ADP forms ATP
            –metabolic money!
• Substrate level phosphorylation
  – chemical energy
• Oxidative phosphorylation
  – energy from proton motive force
• Photophosphorylation
  – radiant energy
      Heterotrophic Metabolism
• Oxidize organic energy source releasing
  electrons
• Typically utilize carbohydrates (CH2O)
  – Glucose is #1 source
• Three possible pathways based on final
  electron receptor
       –Aerobic respiration
       –Anaerobic respiration
       –Fermentation
pathways are
amphibolic and
provide
 • Energy
 • Reducing power
 • Precursor metabolites
– Respiration uses reducing power to generate ATP
  • NADH and FADH2 provide electrons to power proton
    motive force

  • Terminal electron acceptor varies
     – Oxygen in aerobic respiration
     – Anaerobic respiration uses alternate inorganic
       molecule
                 GLYCOLYSIS
• Embden-Meyerhof Pathway
• Common pathway
• Glucose (6C) partially broken down into 2
  molecules of pyruvate (3C)
  – Anerobic; cytoplasm
• 2 NADH; 4 ATP
• 2 ATP consumed; so net gain of 2 ATP
  – Substrate level phosphorylation
• Pentose phosphate pathway
  – Oxidizes Glucose-6-phosphate
    • Produces glyceraldehyde 3-phosphate, Fructose
      6-phosphate and CO2
    • If only 5 carbon sugars are available it can
      biosynthesize 6 carbon sugars


  – Major contributor to biosynthesis
    • reducing power in NADPH
    • vital precursor metabolites for anabolic pathways
    • Intermediates may be used to generate ATP
Pentose phosphate pathway
• Entner-Doudoroff pathway
  – Alternate pathway to glycolysis
  – typically not seen in G+ bacteria
  – major contributor to biosynthesis
    • reducing power in NADPH
    • vital precursor metabolites for anabolic pathways
Entner-Doudoroff pathway

								
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