1. Dark Reactions & Photosynthesis AP Biology Ms. Day
Chapter 10 (Part 3)
Dark Reactions & Photosynthesis
AP Biology
Ms. Day

3. 1. What is the overall equation of photosynthesis. 2
1. What is the overall equation of photosynthesis? 2. Using prior knowledge, how is each reactant/product used in photosynthesis overall?
Discuss and write it out in your lab group.

4. 6H2O + 6CO2  6O2 + C6H12O6 H2O  ? CO2  ? O2  ? C6H12O6  ?

5. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
Is similar to the citric acid cycle in mitochondria
Occurs in the stroma

6. The Calvin cycle has three phases 1. Carbon fixation 2. Reduction 3
The Calvin cycle has three phases 1. Carbon fixation 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP)

7. In small groups…discuss what you think are the meaning of these words: 1. Carbon fixation? 2. Reduction? 3. Regeneration?

8. 1. Carbon fixation 2. Reduction 3. Regeneration
Converting (or “fixing”) carbon into another molecule
2. Reduction
Accepting electrons from another substance
3. Regeneration
Remake something

9. STEP #1: CARBON FIXATION Enzyme RUBISCO catalyzes reaction
The Calvin Cycle Steps
STEP #1: CARBON FIXATION
CO2 enters cycle
Attaches to a 5-C sugar called ribulose biphosphate (RuBP)
6-C molecule (unstable)
Enzyme RUBISCO catalyzes reaction
Unstable 6-C molecule immediately breaks down to 3 3-C molecules called 3- phosphoglycerate (3-PGA)

10. Make a substance inactive Make ATP from ADP and Pi
STEP #2: REDUCTION
3-PGA gets phosphorylated from ATP
________________________________________ _____
In small groups, chose an answer:
What does “phosphorylate” mean?
Give a PO4-3 to something
Take a PO4-3 to something
Make a substance inactive
Make ATP from ADP and Pi
Where does the ATP for this to occur come from?

11. STEP #2: REDUCTION 2. 1,3 PGA is created now
2. NADPH reduces 1,3 PGA to Glyceraldehyde-3-phosphate (G3P)
NADPH gives up e’s and H+’s
G3P = a sugar that stores potential energy
Every 3 CO2  yields 6 G3P’s BUT only 1 can be counted in net gain for carbohydrate (GLUCOSE) production

12. REGENERATION OF CO2 ACCEPTOR (RuBP)
5. 5 G3P’s are rearranged into 3 RuBP molecules
ATP is used !!!!

13. MORE ATP is needed than NADPH!!
The Calvin cycle
NOTE:
MORE ATP is needed than NADPH!!
Phase 1: Carbon fixation
Phase 3: Regeneration of the CO2 acceptor (RuBP)
Phase 2: Reduction
Also known as PGAL

14. Calvin Cycle Overview For 1 G3P molecule made 9 ATP molecules are used
6 NADPH molecules are used
**MORE ATP than NADPH
G3P (aka PGAL) = starting material to make other organic molecules (glucose, starch, etc.)

15. If the Calvin cycle needs more ATP than NADPH, where does the extra ATP come from?
In small groups, chose an answer:
Cellular Respiration
Noncyclic photophosphorylation
ETC #2
Cyclic Photophosphorylation

16. Animations (Dark Reactions)
See dark reaction animations
hill.com/sites/ /student_view0/chapte r5/animation_quiz_1.html
.html
y/Bio231/calvin.html
tent/index/animations.asp

17. CO2
3-PGA
ATP
ADP
RUBISCO
ADP
ATP
1,3 PGA
RuBP
NADPH
G3P
NADP+
G3P
G3P
GLUCOSE