Photosynthesis - Overview

• Photosynthesis reaction


  $6CO2 +$$6H20 +$$Light E =$$C6H12O6+$$6O2$
• Background

  • 2 parts to photosynthesis
  • Light dependent rxns (LDRs) ("photo"; part that involves light) (occurs in TM)
  • Carbon-fixation rxns (light-independent rxns) ("synthesis") (occurs in stroma which has tons of enzymes)
• Light - Dependent rxns Background

  • goal: convert light E into chemical E
  • 2 types of chemical E we need to make : ATP + NADPH
• Summary light-dependant rxn


  $12H2O +$$12NADP^+$$+$$18 ADP +$$18Pi +$$Light --> 6O2 +$$12NADPH +$$18 ATP$

  12H2O + 12NADP^+ + 18 ADP + 18Pi + Light --> 6O2 + 12NADPH + 18 ATP

  *pi is inorganic phosphate molecule*
• 2 types of LDR

  1. Linear electron flow
  2. cyclic electron flow
• Photosystems (LDR)

  • PSI + PSII (photosystem 1 and photosystem 2)
  • located in TM
  • Job: capture light E and transfer excited electron *important*
  • this creates ATP & NADPH
• Within PSI + PSII there are 2 separate complexes that work together

  • light-harvesting complex (has 250 chlorophyll molecules, accessory pigments, & proteins)
  • This area does a lot of the helping
  • captures/ harvesting as much light as possible and transfers to 2nd complex (rxn center)
• Reaction Center

  • has a pair of chlorophyll a molecules
  • e- is located here and is transferred to a primary electron acceptor$1^o$
  • PSI = P700 (absorbs light best at 700 nanometers (nm))
  • PSII = P680 (absorbs light best at 680 nm)