1. Photosynthesis
Photosynthesis with Hank!
Life from Light and Air

2. Obtaining the materials
sunlight
leaves = solar collectors
CO2
stomates = gas exchange
H2O
uptake from roots
nutrients
N, P, K, S, Mg, Fe…

3. Concurrent Reactions

4. Light-Dependent Reactions
*Key to these rxns is light absorption
Success lies in photosystems – 2 part complex
Antenna complex – site of absorption; excites electrons & passes them on
Reaction center – redox-rxns occur here; excited ele- transferred to electron acceptor

5. reaction center
antenna pigments

6. To Calvin Cycle!!!
Stroma
ATP!
NADPH
ADP + P
NADP + + 2H +
PS 700
PS 680
H+ + ½ O2 +
Lumen
- NADP+ Reductase
- Cytochrome complex
- ferredoxin
- pheophytin
- ATP Synthase
- ele -
- plastoquinone
- H + ion

7. Step 1: Light absorbed in PS II excites ele- (from H2O splitting) → passed to electron acceptor (pheophytin)
Step 2: Plastoquinone(PQ) shuttles high energy ele- through series of redox rxns (ETC 1); passes through cytochrome complex, driving in H+, ↑ [H+] = ↓ pH
Step 3: De-energized ele- are passed off to plastocyanin (PC) → PS I re-excites ele- and ferredoxin shuttles through ETC 2
Step 4: a) Ele- reduce NADP+ to NADPH at NADP+ reductase
b) H+ pumped out via ATP Synthase – activates chemiosmosis → production of ATP from ADP

9. Regulation of the Light Reaction
Calvin cycle uses more ATP than NADPH
If there is enough, NADPH production is turned off
ATP
18 ATP + 12 NADPH 
1 C6H12O6

10. Review Animations
Light dependent reactions

11. Light-INdependent Reactions
Want to make C6H12O6 → synthesis
**How? From what? What raw materials are available?
CO2
NADPH
reduces CO2
carbon fixation
NADP
NADP
C6H12O6

12. From CO2  C6H12O6 CO2 has very little chemical energy
fully oxidized
C6H12O6 has a LOT of chemical energy
highly reduced
Synthesis = endergonic process
put in a lot of energy
Reduction of CO2  C6H12O6 proceeds in many small uphill steps
each catalyzed by specific enzyme
uses energy stored in ATP & NADPH ←from light rxns!

13. ribulose bisphosphate carboxylase
Calvin cycle C C C 1C
CO2 C
1. Carbon fixation C
3. Regeneration of RuBP C 5C C
RuBP
RuBisCo C
ribulose bisphosphate 6C
starch, sucrose, cellulose & more
3 ADP
3 ATP C
ribulose bisphosphate carboxylase 5C C
used
to make glucose C
glyceraldehyde-3-P
1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA).
2. The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+.
3. Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose. 3C C
PGA
G3P aka PGAL C
phosphoglycerate C C C 3C C = C C C
6 ADP
6 ATP
2. Reduction C | H C – C
6 NADP
6 NADPH 3C C

14. To G3P and Beyond! Resulting 3-C Sugar G3P  glucose  carbohydrates
- important intermediate
G3P  glucose  carbohydrates
 lipids  phospholipids, fats, waxes
 amino acids  proteins
 nucleic acids  DNA, RNA

15. A little more about RuBisCo…
Enzyme which fixes carbon from air
ribulose bisphosphate carboxylase
the most important enzyme in the world!
**It makes life out of air!**
most abundant enzyme

16. “Banking” Keeping the books straight…
6 turns of Calvin cycle = 1 C6H12O6 (6C)
6 CO2  1 C6H12O6 (6C)
18 ATP + 12 NADPH  1 C6H12O6
Left over ATP from light reactions used elsewhere by cell

17. Sum it Up: Light Reactions
H2O
ATP O2
light
energy  +
NADPH
H2O
sunlight
produces ATP & NADPH
releases O2 as waste
Energy Building
Reactions
NADPH
ATP O2

18. Calvin Cycle  builds sugars uses ATP & NADPH recycles ADP & NADP+ CO2
C6H12O6  +
NADP
ATP
NADPH
ADP
CO2
builds sugars
uses ATP & NADPH
recycles ADP & NADP+
ADP
NADP
Sugar Building
Reactions
NADPH
ATP
sugars

19. Supporting a biosphere
Big Picture: photosynthesis is THE most important process for continuation of life on Earth
Each year photosynthesis…
captures 121 billion tons of CO2
synthesizes 160 billion tons of carbohydrates
heterotrophs depend on plants for food, fuel, & raw materials

20. Light Depedent Review:
Where did the energy come from?
Where did the electrons come from?
Where did the H2O come from?
Where did the O2 come from?
Where did the O2 go?
Where did the H+ come from?
Where did the ATP come from?
What will the ATP be used for?
Where did the NADPH come from?
What will the NADPH be used for?

21. Light Independent Review II:
6CO2
6H2O
C6H12O6
light
energy  +
6O2
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the H2O go?
Where did the energy come from?
What’s the energy used for?
What will the C6H12O6 be used for?
Where did the O2 come from?
Where will the O2 go?
What else is involved…not listed in this equation?

22. Adaptations in Alternative Environments
C4 Path
CO2 stored is mesophyll & released in vascular tissue

23. Adaptations in Alternative Environments
CAM Path
Stomata open at night – CO2 stored in vacuoles for later use

24. Combating Photorespiration
Photorespiration – rxn between RuBP & O2 when [O2] is high → uses ATP & produces CO2
Favored ONLY when [O2] exceeds [CO2]
Store CO2
C4 Path
CAM Plants