Module 5: Photosynthesis

• photosynthesis uses light energy to make ATP and NADH
• photophosphorylation: creates proton gradient across membrane
• the photosynthetic apparatus boosts energy of e-
• what are the products of photosynthesis?

  oxygen, sulfur, or sulfate
• dark reactions fix CO2 using energy from light reactions
• the photosynthetic apparatus contains light harvesting complex, reaction center, and electron transport chain
• light harvesting complex funnels photons to reaction center, contains protein and pigments
• carotenoids in light harvesting complex protect reaction center by dissipating energy
• alternating double bonds in carotenoids create large pi orbitals that absorb high energy electrions
• how do carotenoids protect the reaction center?

  quench triplet state chlorophyll which can pass e- to form reactive singlet oxygen
• pigments in light harvesting center are positioned near the outside of the cell for maximum light collection, efficient energy and electron transfer
• reaction center is concentrated light energy
• what is the special pair in the reaction center?

  bacteriochlorophyll, creates excited e-
• in the reaction center photons (light energy) excite electron to higher orbital (chemical energy)
• anoxygenic synthesis does not generate oxygen, variety of e- sources
• what types of bacteria have anoxygenic synthesis?

  purple and green bacteria, heliobacteria
• oxygenic photosynthesis: generates oxygen, H2O is electron source
• what types of bacteria have oxygenic photosynthesis?


  cyanobacteria
• purple bacteria produce sulfur or sulfate
• why are purple bacteria good research models?


  can grow in dark using fructose
• purple bacterial photosystem is in the intracytoplasmic membrane, has core and peripheral light harvesting complexes
• what light harvesting complex changes number in purple bacteria>?

  peripheral increases in low light
• green bacteria harvest light via chlorosome
• green bacteria are a distinct group, not closely related to other phototrophs
• in green bacteria, bchl is held in place by crystalline array
• cyanobacteria have oxygenic photosynthesis
• cyanobacteria have thylakoid membrane and phycobiliproteins to harvest light
• cyanobacteria have 2 photosystems, combination of purple and green bacteria reaction centers
• retinal-based phototrophy: makes ATP from light without reaction center or chlorophyll
• retinal-based phototrophy requires a single protein with light-sensitive pigment retinal that forms proton gradient by conformational change
• dark reactions are anabolism
• retinal based phototrophy and photosynthesis both have:

  • light-driven proton gradient
  • ATP synthase
  • light reactive pigments
• how is photosynthesis different from retinal-based phototrophy?

  • light harvesting proteins and reaction center
  • chlorophyll light pigment (vs. retinal)
  • electron transport chain to make NADH
  • cytochromes
  • quinones