Overview of Cellular Respiration and Photosynthesis

High Energy and Low Energy Forms

• Energy Forms:
  • High Energy: ADP, NADH, FADH2, NADPH
  • Low Energy: ATP
• Role of High Energy Forms:
  • Serve as carriers of energetic electrons during photosynthesis.
  • Transfer energy to ATP which is utilized in cellular processes.

Introduction to the Calvin Cycle

• Calvin Cycle:
  • The process where carbon dioxide (CO2) is fixed to produce glucose.
• Importance of High Energy Carriers:
  • ATP and NADPH from light-dependent reactions are utilized for glucose synthesis.

Electron Transport Chain in Photosynthesis

• Electron Pathway:
  • Electrons originate from water molecules.
  • They move through:
  • Photosystem II
  • Photosystem I
  • NADP reductase
  • Final Destination: NADPH, which stores energy for Calvin cycle.

Processes in the Calvin Cycle

Carbon Fixation

• Starting Molecule: Ribulose bisphosphate (RuBP) - 5 carbons.
• Input: 6 carbon dioxide (CO2) molecules are fixed.
• Result:
  • Carbon Count Calculation:
  • 6 RuBP (5 carbons each) + 6 CO2 (1 carbon each) = 6 RuBP (6 carbons each) in total = 36 carbons.

Splitting of Carbon Molecules

• Process:
  • The 6 carbon molecules are split in half.
• Result:
  • Produces 12 molecules of 3-carbon molecules called Phosphoglycerate (PGA).

Carbon Reduction Phase

• Conversion Process:
  • PGA (12 molecules) are reduced to Glyceraldehyde-3-phosphate (G3P).
• Energy Requirements:
  • Utilizes 12 ATP molecules and 12 NADPH molecules.
• Definitions:
  • Reduction: G3P has higher energy than PGA.
  • Oxidation: NADPH is oxidized during the reduction of PGA.

Returning to RuBP

• G3P Production:
  • From the 12 G3P molecules, 2 G3P leave the cycle for glucose production.
• Remaining 10 G3P molecules regenerate RuBP.
• Conversion to Glucose:
  • Two 3-carbon G3P molecules (x2) combine to form one 6-carbon glucose.
  • Total Carbons Calculation:
  • 10 G3P (3 carbons each) = 30 carbons remain for regeneration of RuBP.

RuBP Regeneration Phase

• Final Steps:
  • 10 G3P molecules are rearranged to regenerate RuBP.
• Energy Requirement:
  • The regeneration of RuBP utilizes 6 ATP molecules for completion.

General Summary of Light Reactions and the Calvin Cycle

• Light Dependent Reactions:
  • Electrons are excited by light energy starting at Photosystem II then moving to Photosystem I…introduction of water splitting after the light capture.
• Z Scheme:
  • Represents the non-cyclic electron transport pathway, showing the sequential steps of light-induced electron excitation and energy conversion into chemical form.
• Key Takeaway:
  • Photosynthesis is about converting light energy into chemical energy, which in turn is used to fix carbon dioxide into sugars during the Calvin cycle.