Photosynthesis and the Calvin Cycle Notes

Introduction to Photosynthesis

Plants make their own food through photosynthesis.
Reactants: Carbon dioxide (CO2), water (H2O), and sunlight.
Products: Glucose (C6H12O6) and oxygen (O2).
- Glucose is the main source of energy for plants.
- Oxygen is released as a byproduct.

Occur in the presence of sunlight.
Involves:
- Water (H2O)
- ADP+
- NADP+
Products of Light Reactions:
- ATP (energy currency)
- NADPH (electron carrier)
- Oxygen (byproduct)
Glucose is not produced in this phase; only energy carriers (ATP and NADPH) are generated.

Also known as the Calvin Cycle or dark reactions (does not occur at night).
Key points:
- Uses ATP and NADPH from light reactions to convert CO2 into glucose.
- Occurs during the day but does not require direct sunlight.

Carboxylation Phase:
- Catalyzed by enzyme Rubisco (ribulose bisphosphate carboxylase/oxygenase).
- CO2 is added to ribulose bisphosphate (RuBP, a 5-carbon molecule).
- Produces a 6-carbon intermediate, which immediately breaks down into two 3-phosphoglyceric acid (PGA) molecules.
Reduction Phase:
- Converts PGA to glyceraldehyde 3-phosphate (G3P) using ATP and NADPH.
- Two G3P molecules are produced from two PGA molecules.
Regeneration Phase:
- One G3P is used to form glucose, while the other is used to regenerate RuBP.
- This regeneration also uses ATP to convert back into ADP.

For every 3 CO2 molecules, 3 RuBP molecules are required.
Results in:
- 6 molecules of PGA.
- These convert to 6 G3P, where 1 goes to glucose and 5 regenerate RuBP.
To produce 1 glucose molecule (C6H12O6), the cycle must turn 6 times.

For every turn of the cycle:
- 2 ATP and 1 NADPH are needed for each CO2 fixed.
Total for 6 turns (to produce 1 glucose):
- 18 ATP and 12 NADPH consumed.

The Calvin Cycle is essential for converting inorganic CO2 into organic glucose.
Involves multiple steps and energy transformation, highlighting the intricate relationship between light-dependent and light-independent reactions.