1. Photosynthesis

2. Visible Light: absorption spectra
What structures absorb the light? PIGMENTS
Chlorophyll a (dominant pigment)
absorbs best in red & blue wavelengths & least in green
Chlorophyll b, carotenoids, anthocyanins, xanthophylls (accessory pigments)
Why are plants green? Reflect GREEN light

3. It’s the Dark Reactions!
Photosynthesis
Light reactions
convert solar energy to chemical energy
ATP & NADPH
Calvin cycle
sugar production reactions
Uses (ATP & NADPH) to reduce CO2 & synthesize C6H12O6
It’s the Dark Reactions!

4. Light Reaction Absorbs light to excite electrons
Oxidation of H2O forming O2 (Photolysis!)
Electrons replaced
H+ concentration building
Oxygen is released

5. Linear Electron Flow “Noncyclic photophosphorylation”
PS II generates energy as ATP
PS I generates energy as NADPH
1 photosystem is not enough.
Have to lift electron in 2 stages to a higher energy level. Does work as it falls.
First, produce ATP -- but producing ATP is not enough.
Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!

6. Light Reaction con’t… Electron Transport Chain
Pumps H+’s to maintain gradient
NADP+ final e- acceptor in chain = NADPH
Chemiosmosis to generate ATP
Diffusion of H+’s down gradient into Stroma

7. Light Reaction of Photosynthesis
Photosystem II
Photosystem I
Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide
Video
Video

8. Comparing Chemiosmosis
Not accidental that these 2 systems are similar, because both derived from the same primitive ancestor.

9. Moving on to Calvin cycle
Location: stroma
Uses products of light reactions to drive synthesis reactions
ATP
NADPH

10. From CO2  C6H12O6 CO2 has very little chemical energy
fully oxidized
C6H12O6 contains a lot of chemical energy
reduced
endergonic
Reduction of CO2  C6H12O6 proceeds in many small steps
each catalyzed by specific enzyme

11. Calvin cycle 1C 5C 6C 3C 3C 3C 2x x2 2x CO2 3. Regeneration of RuBP
(3 CO2 enter one at a time) 1C
CO2
ribulose
bisphosphate
3. Regeneration
of RuBP
1. Carbon fixation 5C
RuBP
Rubisco 6C
3 ADP
3 ATP
-enzyme that
Binds CO2
to RuBP
PGAL
to make
glucose 3C 2x
PGA 3C x2
PGAL
sucrose
cellulose
etc.
RuBP = ribulose bisphosphate
Rubisco = ribulose bisphosphate carboxylase
PGA = phosphoglycerate
PGAL = phosphoglyceraldehyde
2. Reduction
6 NADP
6 NADPH
6 ADP
6 ATP 3C 2x

12. Calvin cycle 6 turns of Calvin Cycle = 1 glucose
6 CO2 is needed
18 ATP is needed
12 NADPH is needed
PGAL  important intermediate!
can be used to make:
Glucose, sucrose, lipids, amino acids etc.

13. Summary Light reactions Calvin cycle ADP NADP produced ATP
produced NADPH
consumed H2O
produced O2 as by product
Calvin cycle
consumed CO2
produced Glucose
regenerated ADP
regenerated NADP
ADP
NADP

14. Factors that affect Photosynthesis
Enzymes are responsible for several photosynthetic processes, therefore, temperature and pH can affect the rate of photosynthesis.
The amount and type of light can affect the rate.
A shortage of any of the reactants,CO2 and/or H2O, can affect the rate.

15. The Great Circle of Life!
Energy Cycle
sun
Photosynthesis
glucose O2
H2O
CO2
Cellular Respiration
The Great Circle of Life!
Where’s Mufasa?
ATP