Photosynthesis

• Stroma


  The region of the chloroplast between the inner membrane and the thylakoid membrane
• Light reactions


  Take place in the thylakoid disks
• Dark reactions


  Occur in the stroma
• Oxygen production

  Primarily occurs in the thylakoid disks
• CO2 reduction

  Primarily occurs in the stroma
• Accessory pigments

  Transfer energy to reaction center chlorophylls
• Photosynthetic bacteria which do not use water as the ultimate source of electrons do not produce oxygen
• Magnesium


  Key element at the center of chlorophyll
• Cyanobacteria contain only chlorophyll a
• Two different types of chlorophyll are used by most plants because they allow for absorbing light from a larger portion of the light spectrum
• Wavelengths responsible for light phase reactions

  Blue and red
• Green plants contain both chlorophyll a and chlorophyll b
• Chlorophyll differs from heme because it

  contains magnesium rather than iron
• Light with short wavelengths has more energy than light with long wavelengths
• Reaction centers


  Contain a specialized pair of chlorophylls
• Light reactions


  Drive the redox process involving H2O/O2 and NADP+/NADPH
• NADPH is not a component of the electron transport chain linking Photosystem I and Photosystem II
• Light phase of photosynthesis


  Is closest to the electron transport system
• ATP synthesis in chloroplasts

  Is referred to as photophosphorylation
• The transfer of electrons from water to NADP+ to produce oxygen and NADPH is not a highly exergonic process
• Photophosphorylation


  Results from the proton gradient across the thylakoid membrane
• Photosystem II


  Devoted to water oxidation
• P700 is not Photosystem II
• Photosystem I


  Devoted to NADP+ reduction
• NADP+


  Reduced to NADPH
• Carbon dioxide fixation does not take place during the light reactions
• Reducing water and generating oxygen, O2 does not occur during the light phase
• Oxygen evolving complex


  A manganese-containing protein
• Electrons used in photosynthesis

  First come from water (H2O)
• Reactions during the light phase of photosynthesis

  1. Light absorption in photosystem II

  2. Formation of O2 from water

  3. Formation of NADPH

  4. Formation of ATP

  5. Light absorption in photosystem I
• Pheophytins


  Contain no metal ion in their centers
• The electrons being transferred can take either of two possible paths
• Parts of the electron transport chain in photosynthesis are similar to the electron transport chain in mitochondria
• The mobile electron carrier from Photosystem II to the cytochrome b6f complex is not cytochrome c, pheophytin, plastocyanin, or ferredoxin
• Cyclic electron transport


  Only Photosystem I is involved
• During Z-scheme photosynthesis, ferredoxin does not oxidize NADPH
• Ferredoxin is not important in photosynthesis for forming NADH
• If a plant is actively synthesizing starch from glucose

  There will be more cyclic photophosphorylation and less Z-scheme photosynthesis
• If a plant is using the C4 Hatch-Slack pathway

  There will be more cyclic photophosphorylation and less Z-scheme photosynthesis
• If a plant is actively engaged in a large amount of reductive biosynthesis, requiring NADPH


  There will be more Z-scheme photosynthesis and less cyclic photophosphorylation