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  1. List examples of C1 compounds
    • Methane (CH4)
    • Methanol (CH3OH)
    • Methylamine (CH3NH2)
    • Formate (HCOOH)
    • Formaldehyde (HCHO)
    • Used by methylotrophs (use C1 compounds other than CO2 for energy and carbon)
    • Other organisms can oxidize C1 compounds to CO2 for use
  2. What is C1 metabolism?
    • CO2 metabolism carried out by autotrophs
    • Only prokaryotes can perform
    • Autotrophs: use CO2 as carbon source
    • Photoautotrophs: energy source = light
    • Chemoautotrophs: energy source = inorganic chemicals
  3. What are the three pathways involved in autotrophic carbon fixation? (general)
    • Calvin Cycle
    • Acetyl-CoA pathway
    • Reductive TCA pathway
  4. Details about the Calvin Cycle (not the process)
    • Stage 2 of photosynthesis (Dark reactions)
    • Converts CO2 -> PGALD
    • Aerobic conditions (no obligate anaerobes or microaerophiles)
    • Occurs in cytosol of bacteria, stroma of chloroplasts
    • Not found in archaea
    • Archaea, obligate anaerobes, microaerophiles use rTCA pathway and acetyl CoA pathway
    • Uses two unique enzymes: RuMP kinase (ribulose monophosphate kinase)
    • RuBP carboxylase (Ribulose bisphosphate decarboxylase / Rubisco)
    • Ultimate result is C molecules from CO2 fixed into C6H12O6
    • Shares reactions with glycolysis and PPP
  5. Describe the calvin cycle- phase 1 (detail)
    • Carboxylation of RuBP
    • Rubisco catalyzes bonding of CO2 to RuBP to create an UNSTABLE 6-carbon molecule which instantly SPLITS into 2 3-carbon molecules (3-phosphoglycerate)
  6. Describe the calvin cycle- phase 2 (detail)
    • 3-Phosphoglycerate is phosphorylated by ATP to create 1,3-bisphosphoglycerate
    • 1,3-bisphosphoglycerate reduced to G3P (glyceraldehyde-3-phosphate) by NADPH
    • G3P is an intermediate in glycolysis
  7. Describe the Calvin cycle- phase 3 (detail)
    • For every 6 molecules of G3P created...
    • 5 G3P are phosphorylated by ATPs to regenerate RuBP (combines with CO2 beginning of calvin cycle)
    • One is used for organic compounds
  8. Describe the Acetyl-CoA pathway
    • Used only by microorganisms: archaea, obligate anaerobes, and microaerophiles
    • Key enzyme is carbon monoxodize dehydrogenase: reduces CO2 -> acetyl CoA
    • Acetyl-CoA is made from CO2 and H
    • 1. Reduction of one CO2 to a methyl group [CH3] bound to B12 cofactor
    • 2. [CH3] is transferred to carbon monoxide dehydrogenase
    • CMdehydrogenase catalyzes another rxn that reduces a second CO2 to [C=O]
    • 3. Bound [CH3] and [C=O] -> bound [CH3CO]
    • 4. Bound [CH3CO] + bound [CoASH] -> Acetyl-CoA
    • Afterward, some bacteria convert Acetyl-CoA to acetate which is either assimilated into cell material or excreted as waste (to keep pathway moving forward)
  9. Describe the Reductive TCA cycle
    • Found in photosynthetic green sulfur bacteria, archaea, anaerobes, and microaerophiles
    • Produces oxalocacetate from CO2 via two carboxylation reactions (reverse of TCA cycle)
    • TCA cycle: Acetyl CoA -> 2CO2 +energy
    • rTCA cycle: 2CO2 +8H (from NADH or FADH) + 2ATP -> Acetyl CoA
    • Key enzyme ATP citrate lyase (cleaves citrate [6C] into oxaloacetate [4C] and acetyl CoA [2C]
    • Oxaloacetate can be source of cell C, used for growth
    • Acetyl Coa used to regenerate PEP (Acetyl-CoA carboxylated to pyruvate, then phosphorylated)

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2013-04-29 15:10:05

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