1. Metabolic Processes
Photosynthesis

2. Leaf Structure
You should be able to name the major parts of a leaf and identify where the major reactants and products of photosynthesis come from!

3. Sun vs Shade

4. Photosynthesis INTRODUCTION:
metabolic process occurring in green plants, algae, some protists and cyanobacteria
Photosynthesis is an anabolic PROCESS (building organic molecules which store radiant energy as chemical potential energy)
Recall: Cellular Respiration is a catabolic PROCESS

5. Photosynthesis
Summary Reaction for Photosynthesis:

6. Photosynthesis
CO2:
used in light independent reactions (sometimes called dark reactions)
enters through stomata and goes to mesophyll cells

7. H2O:
used in light dependent reactions (sometimes called light reactions)
enters through veins of leaf and goes to mesophyll cells

8. chlorophyll:
light absorbing green coloured pigment that begins the process of photosynthesis
found in chloroplasts
primary function:
convert light energy into ATP and NADPH in order to be used to convert CO2 to organic molecules

9. Location of Photosynthesis
Chloroplast
organelle involved in photosynthesis
contains its own:
(a) DNA
(b) protein making machinery
You should be able to:
- label a diagram of a chloroplast
- explain the structure/function of the chloroplast

10. Overview of Photosynthetis
Photosynthesis consists of two complex series of events;
Photo Stage (2 stages)
Synthesis Stage

11. Overview of Photosynthesis
Light Dependent Reactions
Capturing light energy
occur within the thylakoid membrane of the chloroplast
produces:
(1) ATP
(2) NADPH
(nicotinamide adenine dinucleotide phosphate, a coenzyme; similar to NADH)

12. Overview of Photosynthesis
Light Independent Reactions OR
CARBON FIXATION DURING CALVIN-BENSON CYCLE
occur in either the presence or absence of light
occur within the stroma of the chloroplast
uses ATP and NADPH from the light reactions to form organic molecules like glucose, from CO2
produces:
(1) sugars
(2) NADP+
(3) ADP

13. Stages
1 & 2
of Photo Stage
Stage 3
Note: Stage 3 used to be called dark reaction, but now we think that the enzymes needed in this reaction, need light

14. Light

15. Light Light Electromagnetic (EM) radiation
Travels in wave packets called photons
Photons with short wavelength = high energy
Photons with large wavelength = low energy

16. Light Light is a mix of photons of diff energies
Most of it we can’t see
If passed through spectroscope, photons can separate from one another
Called
Electromagnetic
spectrum

17. Light – Photosystems (briefly)
Clusters of photosynthetic pigments embedded in thylakoid membrane
They absorb photons of particular wavelengths
Through light reactions they convert ADP to ATP and NADP+ to NADPH
Occurs in the stroma, but receives the energy and atoms to do this from the thylakoid

18. Photosynthetic Pigments
Chlorophyll
found within chloroplasts
Green pigments
contain:
(1) porphyrin ring (hydrophilic)
(2) phytol tail (hydrophobic – allows it
to embed into thylakoid membrane

19. **add this to your EM spectrum above 
chlorophyll a: absorbs 430 and 660 wavelength photons (reaction centre of a photosystem)
chlorophyll b: absorbs 450 and 640 wavelength photons (accessory pigment)
**add this to your EM spectrum above 

20. Photosynthetic Pigments
Carotenoids
Red and yellow pigments (accessory pigments)
Excess energy absorber to protect chlorophyll and dissipate it as heat
E.g. β-carotene from carrots

21. So why are plants green?
Chlorophylls a and b absorb blue-violet and red
But...they reflect those with wavelengths between about 500 nm and 600 nm, which is....
green!

22. So why are plants other colours too?
Different accessory pigments have different colours (e.g. Xanthophylls are yellow)
In the fall, chlorophyll breaks down so other pigments are more visible

23. Ideal Wavelength of Photosynthesis
Photosynthetically Active Radiation
Ideal wavelengths for photosynthesis
Ranges from 400 nm to 700 nm
Combination of
chlorophyll a and b,
and all of the other
accessory pigments
that “help out”
That’s why you can’t
grow plants under
regular lightbulbs 

24. Photosynthesis
Question: page 159 # 3-6, page 165 #1, 2

25. Photosynthesis
The Details

26. Photosynthesis: Light Reactions
Light reactions begin when photons strike a photosynthetic membrane.
Can be divided into 3 parts
Photoexcitation: absorption of a photon by an electron of chlorophyll
Electron transport – creates an H+ reservoir
Chemiosmosis – movement of protons to help phosphorylate ADP to ATP

27. Photosynthesis: Photosystems
In order to capture light energy, electrons must become excited and leave a molecule.
Only chlorophyll a can pass electrons along to the primary electron acceptor.
Pigments group together on the thylakoid membrane in photosystems. Antenna and accessory pigments capture light energy and pass it to chlorophyll a.

28. Photosystem What you were looking at......
Location and structure of chlorophyll molecules in plants

29. Photosynthesis: Photosystems
consists of:
Reaction centre (chlorophyll a)
Antenna complex (hundreds of chlorophyll molecules and accessory pigments)
Location of Photosystems:
Thylakoid membrane

30. Types of photosystems Photosystem I Photosystem II
Chlorophyll a molecule is called P700 (red light)
Photosystem II
Chlorophyll a molecule is called P680 (red light)
pigment
Wavelength (nm)

31. Types of Photosystems
There are two separate light powered systems in the membranes of the thylakoid disc:
Non-cyclic Photophosphorylation
Cyclic Photophosphorylation

32. Non-Cyclic Photophosphorylation
Used in photosynthesis of green plants
Involves both photosystem I (PS I) and photosystem II (PS II)
Chlorophyll a electrons are passed along to make NADPH and are replaced by water’s electrons
Produces ATP and NADPH

33. Non-Cyclic Photophosphorylation

34. Non-Cyclic Phos. - Description
PS II absorbs light energy causing two electrons of chlorophyll P680 to become excited.
A Z protein, associated with PS II and facing the thylakoid lumen, splits water into oxygen , protons, and electrons
Two electrons are used to replace the excited electrons in chlorophyll P680. Oxygen leaves the chloroplast as a byproduct.
The protons remain in the thylakoid space add to the proton gradient that powers chemiosmosis.

35. Non-Cyclic Phos. - Description
The two excited electrons travel through a series of proteins within the thylakoid membrane
4. As the two excited electrons move from the excited reaction centre of PS II to plastoquinone (PQ), energy is lost.
5. This energy is used to move 4 protons from the stroma to the lumen.
This creates a proton gradient for chemiosmosis.

36. Non-Cyclic Phos. - Description
The increase in proton concentration within the thylakoid lumen drives protons out of the lumen to the stroma via a special protein called ATP Synthase
This proton motive force is used to produce ATP!

37. Non-Cyclic Phos. - Description
7. The electrons continue to move from PQ to other components of the electron transport chain (cytochrome b6-f complex to Plastocyanin) to PS I eventually replacing the 2 electrons that were lost by PS I when it was struck by photons.

38. Non-Cyclic Phos. - Description
8. The two excited electrons from PS I pass through another electron transport chain containing the protein ferradoxin (Fd). 9. The two excited electrons are then captured by NADP reductase which uses the two electrons and protons from the stroma to reduce NADP+ to NADPH.

39. Non-Cyclic Phos. - Description
The ATP and NADPH are used to drive light independent reactions.
So...
ATP is generated from reactions stemming from PS II
NADPH is generated from reactions stemming from PS I (that gained e- from PSII)

40. The Two Photosystems & The 3 Light Dependent Processes
Photosystem II
Photosystem I
Photoexcitation
Electron Transport
Chemiosmosis

41. Non-Cyclic….generally…
OK – the Light Reaction Details!
Animation!
Involves Photosystem I and II where the chlorophyll a electrons are passed along to make NADPH, and are replaced by H2O’s electrons

42. Cyclic Photophosphorylation
Used by prokaryotes
Photosystem I only (so P700)
the chlorophyll a electrons return to chlorophyll a (hence…cyclic)
Product = ATP (no NADPH is made)

43. Cyclic Photophosphorylation

44. Cyclic Photophosphorylation: Description
PS I (P700) absorbs photo energy, causing the two electron to become excited.
The two excited electrons enter an electron transport chain

45. Cyclic Photophosphorylation
3. The two excited electrons are captured by the protein ferradoxin , causing some of their energy to be lost.
The two excited electrons are then captured by the cytochrome b6-f protein complex and lose more energy.
At this point, enough energy has been lost to add a P to ADP forming
ATP.

46. Cyclic Photophosphorylation
5. The passing of electrons from cytochrome b6-f complex to the next electron carrier, plastocyanin (Pc) results in further lowering of the energy in the electrons to almost the ground state
The passing of the two electrons to P700 returns the
electrons to both the original molecule and the ground state.

47. Cyclic Flow...generally...
Involves Photosystem I only where the chlorophyll a electrons return to chlorophyll a (no NADPH is made)

48. Homework 
Page 165 # 4-6, 10-12, 15
Read your text up until the end of light independent reactions

49. Photosynthesis
Light Independent Reactions

50. Light Independent Reactions
Calvin Cycle
A.k.a. C3 photosynthesis
Due to the first compound produced contains three carbons
reactions that convert carbon dioxide into sugar molecules
occur in the stroma of chloroplasts

52. Stage One: Carbon Fixation
CO2 and RuBP unstable 6 Carbon intermediate which splits into 2, 3 carbon PGA
Note that we start with 3 CO2 to produce 6 molecules of PGA
Rubisco

53. Stage Two: Reduction Reactions
3-PGA is phosphorylated by an ATP  molecule 1,3-BPG
Note there are really 6 molecules, so we need 6 ATP
6 NADPH reduces 6 1,3-BPG  6 G3P or PGAL
1 G3P (1/2 a glucose) exits cycle as final product (5 move on in cycle)

54. Stage Three: Regeneration of RuBP
Remaining 5 G3P: rearranged  3 RuBP
Use 3 ATP
Cycle continues
G3P molecules that leave are used to synthesize larger sugars (e.g.glucose)
Note: 2 Pi is removed...count your phosphates!

55. Notes: Rubisco (an enzyme)
Ribulose biphosphate carboxylase/oxygenase
Most abundant protein on Earth
3 CO2 must be fixed before 1 G3P molecule can be removed from the cycle
6 turns of the cycle makes one 6 C glucose molecule (looking at one CO2 at a time)

56. Homework 
Page 167 # 13-18

57. Do questions: page 166 – 167, # 2 – 9
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