Final Final

  1. Phototrophy is
    The harnessing of photoexcited electrons to power cell growth
  2. Bacteriorhodopsin is
    • -A single-protein, light-driven proton pump
    • -Found in halophilic archaea
    • -A homolog, proteorhodopsin, is found in marine proteobacteria.
  3. Retinal
    • Is linked to lysine residue and absorbs photon and shift from trans to cis.
    • Surround by seven alpha helices of bacteriorphodopsin in alternating directions.
    • The cycle of excitation and relaxation back to the trans form is coupled to pumping of 1H+ from the cytoplasm across the membrane.
    • The proton gradient thus generated drives ATP synthesis by a typical F1Fo ATP synthase.
  4. The energy for photosynthesis derives from
    The photoexcitation of a light-absorbing pigment.
  5. All forms of photolysis share a common design:
    • 1.Antenna system
    • 2.Reaction center complex
    • 3.Electron transport system
    • 4.Energy carriers
  6. Photosystem I
    • Found in chlorobia, “green sulfur” bacteria
    • Separates electrons associated with hydrogens from H2S or an organic electron donor such as succinate, or even from reduced iron (Fe2+)
    • Electrons are ultimately transferred to NAD+ or NADP+.
    • - The reduced carrier (NADH or NADPH) provides reductive energy for CO2 fixation and biosynthesis.
    • Bacteria using PSI also generate a net proton gradient to drive ATP synthesis.
  7. Photosystem II
    • Found in alphaproteobacteria, “purple nonsulfur” bacteria
    • Separates an electron from bacteriochlorophyll itself
    • Electrons are then transferred to an ETS.
    • Ultimately, an electron is returned to bacteriochlorophyll.
    • This process, which generates ATP, is called cyclic photophosphorylation.
    • PSII, unlike PSI, provides no direct way to make NADH or NADPH for reductive biosynthesis.
  8. Oxygenic Z Pathway
    • Found in cyanobacteria and chloroplasts
    • Includes homologs of PSI and PSII
    • Eight photons are absorbed and two electron pairs are removed from 2H2O, ultimately producing O2.
    • Oxygenic photosynthesis forms 3 ATP + 2 NADPH per 2 H2O photolyzed and O2 produced.
    • - The ATP and NADPH are used to fix CO2 into biomass
  9. Calvin cycle
    • 1. Carboxylation and splitting: 6C → 2[3C]
    • - Ribulose 1,5-bisphosphate condenses with CO2 and H2O to form a 6C molecule, which immediately splits into two 3-phosphoglycerate (PGA) molecules.
    • - Reactions are catalyzed by Rubisco.
    • 2. Reduction of PGA to G3P
    • - The carboxyl group of PGA is phosphorylated by ATP, and then hydrolyzed and reduced by NADPH.
    • - This generates glyceraldehyde 3-phosphate.
    • 3. Regeneration of ribulose
    • 1,5-bisphosphate
    • - One of every six G3P is converted to glucose.
    • - The other five molecules enter a series of reactions that regenerate three molecules of ribulose 1,5- bisphosphate.
  10. Carboxysomes
    Takes up bicarbonate (HCO3–), which is then immediately converted to CO2 by carbonic anhydrase.
  11. The reductive, or reverse, TCA cycle:
    • Uses 4–5 ATPs to fix four molecules of CO2 and generate one oxaloacetate
    • Reduction is performed by NADPH or NADH and by reduced ferredoxin (FDH2).
  12. Reductive acetyl-CoA pathway
    • Used by anaerobic soil bacteria, autotrophic sulfate reducers, and methanogens
    • Two CO2 molecules are condensed through converging pathways to form the acetyl group of acetyl-CoA.
    • Carbon monoxide is an intermediate.
    • Reducing agent is H2 instead of NADPH
  13. Biosynthesis of Fatty Acids
    • is managed by the fatty acid synthase complex.
    • Molecules of acetyl-CoA are carboxylated to malonyl-CoA.
    • The coenzyme A is replaced by acyl carrier protein (ACP) making malonyl-ACP.
    • Malonyl-ACP condenses with the growing chain.
    • The growing chain now contains a ketone, which is reduced to CH2 by 2 NADPH.
    • Successive addition can continue many times to build a saturated fatty acid of indefinite length.
  14. Regulation of Fatty Acid Synthesis
    • Acetyl-CoA carboxylase regulates its own transcription.
    • Starvation blocks fatty acid synthesis through the “stringent response.”
    • Low temperature favors unsaturated fatty acids by inducing expression of the dehydratase enzyme.
Card Set
Final Final