Production of ATP: Study Notes

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Production of ATP / Chemiosmosis

Process and Key Points

• Proton Gradient:
  • Energy from electrons is used to pump protons into the thylakoid space, establishing a proton gradient.
• ATP Synthase:
  • Protons flow back through ATP synthase, which drives the production of ATP.
• Energy Source:
  • The electron transport chain provides the energy that powers proton pumps and ATP synthesis via chemiosmosis.

Dark Reaction (Calvin-Benson Cycle)

• Takes place in the stroma of the chloroplast.
• Does not require light but needs ATP and NADPH produced during the light reactions.
• Main purpose: To fix carbon dioxide into organic molecules like glucose.

Calvin-Benson Cycle Phases

Phase 1: Carbon Fixation

• CO₂ is fixed by the enzyme RuBisCO.
  • Input: 3 CO₂ + 3 RuBP
  • Output: 6 molecules of 3-phosphoglycerate (3-PGA).
• Three molecules of CO₂ react with three molecules of RuBP (5-carbon compound) to produce six molecules of 3-phosphoglycerate (3-carbon compound).

Phase 2: Reduction Phase

• ATP and NADPH from the light reactions are used to reduce 3-PGA into G3P (Glyceraldehyde-3-phosphate).
  • Input: 6 ATP + 6 NADPH
  • Output: 6 G3P.
• Of the six G3P molecules formed, only one exits the cycle to contribute to glucose synthesis, while the remaining five are used to regenerate RuBP.

Phase 3: Regeneration Phase

• The remaining five G3P molecules are converted back into three RuBP molecules, using three ATP molecules.
  • Input: 3 ATP
  • Output: 3 RuBP.
• This regeneration step ensures the cycle can continue by replenishing RuBP, allowing for continuous CO₂ fixation in subsequent cycles.

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