Photosynthesis Part 4Pages 116 to 117

The Calvin Cycle

The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH

The Calvin cycle has three phases:› Carbon fixation (catalyzed by rubisco)› Reduction› Regeneration of the CO2 acceptor

(RuBP)

The Calvin Cycle

Step 1: Carbon Fixation

Joining carbon from the atmosphere into an organic compound

Rubisco combines 3 CO2 with 3 RuBP (a 5 carbon sugar) forming 3 unstable 6 C molecules

3 Unstable 6 C split into 6 - 3 C molecules of PGA

Step 2: Reduction

Use energy from ATP and NADPH to reduce 6 PGA (6 – 3C) into 6 G3P (6 – 3C)

1 – 3C G3P leaves the cycle (eventually is can join with another 3C G3P to form 6C Glucose

5 – 3C G3P stay in the cycle

Step 3: Regeneration of RuBP

Use ATP to convert 5 – 3C molecules back into 3 – 5C molecules

Calvin Cycle

What are the products?› G3P, ADP + Pi, and NADP+

How much CO2 must be fixed to form glucose?› 6 CO2

What is oxidized?› NADPH to NADP+

What is reduced?› CO2 to G3P eventually Glucose

Photosynthesis Review

Review: 6CO2 + 6H2O Light C6H12O6 + 6O2

Where are the reactants used?› CO2 – Calvin Cycle

› H2O – Light Reactions

› Light – Light Reactions Where are the products produced?

› O2 – Light Reactions

› C6H12O6 – Calvin Cycle