Ch 10 Photosynthesis To make with light

1
Ch 10 Photosynthesis--gt To make with light!
2
LE 10-2
Photoautotrophs Self feeders, producers Use
light and inorganic molecules to make own organic
molecules.
Plants
Unicellular protist
10 µm
Purple sulfur bacteria
1.5 µm
Multicellular algae
Cyanobacteria
40 µm
3

• Heterotrophs (food from others)
• -Consumers
• -Obtain organic material from other organisms
• -Dependent on photoautotrophs for food and
  oxygen

4
Photosynthesis conversion of light energy into
chemical energy
Simplified rxn 6CO2 6H2O light --gt C6H12O6
6O2
5
LE 10-3
Enters through roots
6CO2 6H2O light --gt C6H12O6 6O2
Exits through stomata
Organic molecule for fuel or other
Gas enters through stomata
or used in respiration
6
Two major reactions in photosynthesis
Light-dependent (in thylakoid)
Light-independent aka dark or Calvin cycle (in
stroma)
7
LE 10-7
Light
Chlorophyll in thylakoid membranes
Reflected light
Chloroplast
Stroma
Absorbed light
Granum
Transmitted light
8
LE 10-10
in chlorophyll a
CH3
in chlorophyll b
CHO
Porphyrin ring light-absorbing head of
molecule note magnesium atom at center
Hydrocarbon tail interacts with
hydrophobic regions of proteins inside thylakoid
membranes of chloroplasts H atoms not shown
9
LE 10-9a
Chlorophyll a
Chlorophyll b
Carotenoids
Absorption of light by chloroplast pigments
400
500
600
700
Wavelength of light (nm)
Absorption spectra
10
How do we know that absorption of certain
wavelengths of light by plants stimulates a
chemical reaction in plants?
Specifically how do we know that O2 is a product?
11
LE 10-9c
Aerobic bacteria
Filament of algae
500
600
700
400
Engelmanns experiment (1883) Action spectrum
What would be an important control experiment?
12

• Chlorophyll a
• main photosynthetic pigment
• Accessory pigments
• chlorophyll b and carotenoids absorb excessive
  light that would damage chlorophyll
• broaden the spectrum used for photosynthesis

13
Light-Induced Excitation

• When a pigment absorbs light
• departs from a ground state to an excited state
• --gt unstable Draw
• excited electrons fall back to the ground state,
  give off photons (glow)--gtfluorescence

14
LE 10-11
Excited state
e
Heat
Energy of electron
Photon (fluorescence)
Photon
Ground state
Chlorophyll molecule
Fluorescence
Excitation of isolated chlorophyll molecule
15
LE 10-5_1
Light-dependent rxn in thylakoid
H2O
Light
LIGHT REACTIONS
Chloroplast
16
LE 10-5_2
H2O
Light
LIGHT REACTIONS
ATP
NADPH
Chloroplast
O2
17
LE 10-5_3
Calvin cycle in stroma
H2O
CO2
Light
NADP
ADP
P

i
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
Chloroplast
CH2O (sugar)
O2
18
Photosynthesis as a Redox Process

• Water is oxidized (e- are removed).
• Carbon dioxide is reduced (e- are gained).

19
Two major reactions in photosynthesis
Light dependent (in thylakoid) Creates ATP and
an electron carrier, NADPH Electrons supplied
through splitting and oxidation of H2O
Light -independent (aka dark or Calvin cycle)(in
stroma) Synthesis of organic molecules from
CO2 Reduction reactions Endergonic requires
ATP
20
Light Reaction Consists of 2 photosystems Occu
rs at two different reaction centers each
surrounded by light harvesting complexes
Light harvesting complex funnels energy to
reaction center
21
LE 10-12
Thylakoid
Photosystem
STROMA
Photon
Light-harvesting complexes
Reaction center
Primary electron acceptor
e
Thylakoid membrane
Special chlorophyll a molecules
Pigment molecules
Transfer of energy
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
22
LE 10-13_1
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
CH2O (sugar)
O2
Primary acceptor
Once P680 is oxidized (gives up e-), is it
functional? How is it restored to functionality?
e
Energy of electrons
Light
P680
Photosystem II (PS II)
23
LE 10-13_2
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
CH2O (sugar)
O2
Primary acceptor
e
H2O
2 H

O2
1/2
e
Splitting of H2O yields e- that fill e-hole in
oxidized P680
e
Energy of electrons
Light
P680
Photosystem II (PS II)
24
LE 10-13_3
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
CH2O (sugar)
O2
Primary acceptor
Electron transport chain
Pq
e
H2O
Cytochrome complex
2 H

O2
1/2
Pc
e
e
Energy of electrons
Light
P680
ATP
Photosystem II (PS II)
25
LE 10-13_4
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
CH2O (sugar)
O2
Primary acceptor
Primary acceptor
Electron transport chain
Pq
e
e
H2O
Cytochrome complex
2 H

O2
1/2
Pc
e
e
P700
Energy of electrons
Light
P680
Light
ATP
Photosystem I (PS I)
Photosystem II (PS II)
26
LE 10-13_5
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
Electron Transport chain
O2
CH2O (sugar)
Primary acceptor
Primary acceptor
Electron transport chain
Fd
e
Pq
e
e
e
NADP
H2O
Cytochrome complex
2 H
2 H
NADP reductase

O2
NADPH
1/2
Pc
e
H
P700
Energy of electrons
e
Light
P680
Light
ATP
Photosystem I (PS I)
Photosystem II (PS II)
27
After P700 is oxidized by light energy in PS
I are its missing electrons replaced? If so
what is the electron source?
What would be the effect on photosynthesis if
P700 were not reduced to its original state i.e.
if the e- hole were not filled?
28
Electron Flow

• Noncyclic electron flow
• involves both photosystems (II I)
• produces ATP and NADPH

29
LE 10-14
e
ATP
e
e
NADPH
e
e
e
Mill makes ATP
Photon
e
Photon
Photosystem II
Photosystem I
30
Cyclic Electron Flow

• - Uses only photosystem I
• - Produces only ATP, no NADPH
• - Generates surplus ATP
• to satisfy demand in the Calvin cycle

31
LE 10-15
Primary acceptor
Primary acceptor
Fd
Fd
NADP
Pq
NADP reductase
Cytochrome complex
NADPH
Pc
Photosystem I
ATP
Photosystem II
32
How is ATP made?

• By chemiosmosis

33
LE 10-17
H2O
CO2
Light
NADP
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
O2
CH2O (sugar)
STROMA (Low H concentration)
Cytochrome complex
Photosystem I
Photosystem II
Light
NADP reductase
Light
2 H
NADP 2H
Fd
NADPH
H
Pq
Pc
H2O
O2
1/2
THYLAKOID SPACE (High H concentration)
2 H
2 H
To Calvin cycle
Thylakoid membrane
ATP synthase
STROMA (Low H concentration)
ADP

ATP
P
i
H
34

• Current chemiosmotic model
• H (protons) accumulate in thylakoid space
• 1. Through splitting of water
• 2. By translocation into thylakoid when e- are
  transported
• 3. By removal of H from stroma due to bonding
  with NADPH

• H diffuses from thylakoid space --gt stroma
  through membrane enzyme, ATP synthase

• Movement activates ATP synthase

• ATP synthesized on stromal face where the Calvin
  cycle takes place

35
Products from light reactions power Calvin cycle!
What are the light reaction products?
ATP energy carrier NADPH electron carrier
What is the product of the Calvin cycle?
Glucose (fuel)
What additional molecule must enter the Calvin
cycle to make sugar?
CO2
36

• Calvin cycle
• Three phases
• Carbon fixation (catalyzed by rubisco)
• Reduction
• Regeneration of the CO2 acceptor (RuBP)

37
LE 10-18_1
H2O
CO2
Input
Light
3
(Entering one at a time)
NADP
CO2
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
Phase 1 Carbon fixation
NADPH
Rubisco
CH2O (sugar)
O2
3
P
P
Short-lived intermediate
6
P
3
P
P
3-Phosphoglycerate
Ribulose bisphosphate (RuBP)
6
ATP
6 ADP
CALVIN CYCLE
38
LE 10-18_2
H2O
CO2
Input
Light
(Entering one at a time)
3
NADP
CO2
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
Phase 1 Carbon fixation
NADPH
Rubisco
CH2O (sugar)
O2
3
P
P
Short-lived intermediate
6
P
P
P
3
3-Phosphoglycerate
Ribulose bisphosphate (RuBP)
6
ATP
6 ADP
CALVIN CYCLE
6
P
P
1,3-Bisphosphoglycerate
6
NADPH
6 NADP
6
P
i
6
P
Glyceraldehyde-3-phosphate (G3P)
Phase 2 Reduction
Glucose and other organic compounds
P
1
G3P (a sugar)
Output
39
LE 10-18_3
H2O
CO2
Input
Light
(Entering one at a time)
3
NADP
CO2
ADP
CALVIN CYCLE
LIGHT REACTIONS
ATP
Phase 1 Carbon fixation
NADPH
Rubisco
CH2O (sugar)
O2
3
P
P
Short-lived intermediate
6
P
P
P
3
3-Phosphoglycerate
Ribulose bisphosphate (RuBP)
6
ATP
6 ADP
3 ADP
CALVIN CYCLE
6
P
P
3
ATP
1,3-Bisphosphoglycerate
6
NADPH
Phase 3 Regeneration of the CO2 acceptor (RuBP)
6 NADP
6
P
i
P
5
G3P
6
P
Glyceraldehyde-3-phosphate (G3P)
Phase 2 Reduction
P
1
G3P (a sugar)
Glucose and other organic compounds
Output
40
I had no idea Icould do these things!
41
Alternative mechanisms of carbon fixation in hot,
dry climates

• How to avoid dehydration during day?

close stomata
Consequences? Positive Negative
conserves water but also blocks CO2 uptake
Overall reduces rate of photosynthesis
42
LE 10-20
CAM Crassulacean acid metabolism
Sugarcane
Pineapple
CAM
C4
CO2
CO2
Mesophyll cell
Night
CO2 incorporated into four-carbon organic
acids (carbon fixation)
Organic acid
Organic acid
Bundle- sheath cell
Day
CO2
CO2
Organic acids release CO2 to Calvin cycle
CALVIN CYCLE
CALVIN CYCLE
Sugar
Sugar
Spatial separation of steps
Temporal separation of steps
43
CAM Plants

• CAM plants open stomata at night, incorporating
  CO2 into organic acids
• Stomata closed during the day
• CO2 released from organic acids and used in the
  Calvin cycle
• Photosynthesis can occur during day!

44
The Importance of Photosynthesis A Review

• sunlight stored as chemical energy in organic
  compounds by chloroplasts
• Sugar supplies chemical energy and carbon
  skeletons to synthesize other organic molecules
• Production of food and atmospheric oxygen

45
LE 10-21
Light reactions
Calvin cycle
H2O
CO2
Light
NADP
ADP

P
i
RuBP
3-Phosphoglycerate
Photosystem II Electron transport chain Photosyste
m I
ATP
G3P
Starch (storage)
NADPH
Amino acids Fatty acids
Chloroplast
O2
Sucrose (export)