Photosynthesis Notes

Light Reactions

  • Two photosystems: photosystem I (stroma, absorbs light at 700700 nm) and photosystem II (thylakoids, absorbs light at 680680 nm).
  • Photolysis of water occurs, leading to electron transfer.
  • Oxygen is released due to water breakdown.
  • A proton gradient is generated.
  • Synthesis of 66 ATP and 66 NADPH.

Calvin Cycle (Carbon Fixation Reactions/Dark Reaction)

  • Does not require light.
  • Three main steps: fixation, reduction, and regeneration.

Fixation

  • Rubisco enzyme binds 33 molecules of carbon dioxide to Ribulose 1,5-bisphosphate.
  • Converts it to three unstable intermediate compounds.

Reduction

  • The three unstable intermediates convert to 66 molecules of glyceraldehyde-3-phosphate (PGAL).
  • 66 ATP are consumed (hydrolyzed to ADP and inorganic phosphate).
  • 66 NADPH are consumed (converted to NADP+).

Regeneration

  • One molecule of PGAL is used to synthesize sugars, starch, amino acids, and fatty acids.
  • The remaining five molecules of PGAL are converted back to ribulose 1,5-bisphosphate.
  • Conversion of 55 PGAL to ribulose 1,5-bisphosphate requires 33 ATP.
  • Total ATP consumption in the Calvin cycle is 99 (6 + 3).
  • The remaining 33 ATP are required for photosynthesis.