Title: Photosynthesis
1Photosynthesis
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3Photosynthesis
4(d) Cyanobacteria
40 µm
(a) Plants
(b) Multicellular alga
1 µm
(e) Purple sulfur bacteria
10 µm
(c) Unicellular eukaryotes
5Experimental history
- Jan Baptista van Helmont
- Plants made their own food
- Joseph Priestly
- Plants restored the air
6Experimental history
- Jan Ingenhousz
- Suns energy split CO2
- Carbon Oxygen
- Oxygen was released into air
- Carbon combined with water
- Make carbohydrates
7Experimental history
- Fredrick Forest Blackman
- 1. Initial light reactions are independent of
temperature - 2. Second set of dark reactions are independent
of light - Dependent on CO2 concentrations temperature
- Enzymes involved in light-independent reactions
8Experimental history
- C.B. van Neil
- Looked at light in photosynthesis
- Studied photosynthesis in Bacteria
9C.B. van Neil
- CO2 2H2S ? (CH2O) H2O 2S
- CO2 2H2A ? (CH2O) H2O A2
- CO2 2H2O ? (CH2O) H2O O2
10C.B. van Neil
- O2 produce from plant photosynthesis comes from
splitting water - Not carbon dioxide
- Carbon Fixation
- Uses electrons H from splitting water
- Reduces carbon dioxide into organic molecules
(simple sugars). - Light-independent reaction
11- CO2 2H2O ? (CH2O) H2O O2
- CO2 2H2O ? (CH2O) H2O O2
12Photosynthesis
- Organisms capture energy from sunlight
- Build food molecules
- Rich in chemical energy
- 6CO2 12H2O ?
- C6H12O6 6H2O 6O2
13Photosynthesis
- Captures only 1 of suns energy
- Provides energy for life
- Source of energy when life began
14Photosynthesis
- Photon
- Packets of energy
- UV light photons have greater energy than visible
light - UV light has shorter wavelengths
15Photosynthesis
- Visible light
- Purple shorter wavelengths
- More energetic photons
- Red longer wavelengths
- Less energetic photons
16Spectrum
171 m
10-
10-
nm
nm
1 nm
nm
10
nm
10
(10
nm)
10
m
5
3
3
6
9
3
Micro- waves
Radio waves
Gamma rays
UV
Infrared
X-rays
Visible light
380
450
500
550
600
650
700
750
nm
Shorter wavelength
Longer wavelength
Lower energy
Higher energy
18Absorption Spectrums
- Photon of energy strikes a molecule
- Absorbed by the molecule or lost as heat
- Depends on energy in photon (wavelength)
- Depends on atoms available energy levels
- Specific for each molecule
19Leaf structure
- Stoma (Stomata) opening on leaf
- Exchange of gases.
- Chloroplasts
- Mesophyll layer of leaf
20Chloroplasts
- Thylakoids
- Internal membranes of chloroplasts
- Grana
- Stacks of thylakoids
- Chlorophyll
- Green pigment
- Captures light for photosynthesis
- Membranes of thylakoids
21Chloroplasts
- Stroma
- Semi-liquid substance
- Surrounds thylakoids
- Contain enzymes
- Make organic molecules from carbon dioxide
22Chloroplasts
23Fig. 10-3b
Chloroplast
Outer membrane
Thylakoid
Intermembrane space
Thylakoid space
Granum
Stroma
Inner membrane
1 µm
24Figure 10.4
Leaf cross section
Chloroplasts
Vein
Mesophyll
Stomata
CO2
O2
Chloroplast
Mesophyll cell
Outer membrane
Thylakoid
Intermembrane space
Thylakoid space
Stroma
Granum
20 µm
Inner membrane
1 µm
25Pigments
- Molecules
- Absorb energy in visible range
- Chlorophylls Carotenoids
- Chlorophyll a b
- Absorb photons in the blue-violet red light
26Pigments
- Chlorophyll a main pigment of photosynthesis
- Converts light energy to chemical energy
- Chlorophyll b carotenoids are accessory
pigments - Capture light energy at different wavelengths
27Pigments
28Pigments
Chlorophyll a
Carotenoids
29Chlorophyll structure
- Located in thylakoid membranes
- A porphyrin ring with a Mg in center
- Hydrocarbon tail
- Photons are absorbed by the ring
- Absorbs photons very effectively
- Excites electrons in the ring
30Chlorophyll structure
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sentation\10_07LightAndPigments_A.html
32Carotenoids
- Two carbon rings attached by a carbon chain
- Not as efficient as the Chlorophylls
- Beta carotene (helps eyes)
- Found in carrots and yellow veggies
33Photosystem
- Cluster of photosynthetic pigments
- Membrane of thylakoids (surface)
- Each pigment captures light energy
- Photosystem then gathers energy
- Energy makes ATP NADPH
34Photosystems
- Chlorophyll a molecules
- Accessory pigments (chlorophyll b carotenoids)
- Associated proteins
35Photosystems
- Consists of 2 components
- 1. Antenna (light gathering) complex
- 2. Reaction center
36Photosystem
- 1. Antenna complex
- Gathers photons from sun
- Web of Chlorophyll a molecules
- Held by proteins in membrane
- Accessory pigments carotenoids
- Energy is passed along the pigments to reaction
center
37Photosystems
- 2. Reaction centers
- 2 special chlorophyll a molecules
- Accept the energy
- Chlorophyll a than passes the energized electron
to an acceptor - Acceptor is reduced (quinone)
38Photosystem
39Fig. 10-12
STROMA
Photosystem
Photon
Primary electron acceptor
Light-harvesting complexes
Reaction-center complex
e
Thylakoid membrane
Pigment molecules
Special pair of chlorophyll a molecules
Transfer of energy
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
40Photosystem
STROMA
Reaction- center complex
Light- harvesting complexes
Photon
Primary electron acceptor
Chlorophyll
STROMA
e-
Thylakoid membrane
Thylakoid membrane
Transfer of energy
Special pair of chloro- phyll a molecules
THYLA- KOIDSPACE
Pigment molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Protein subunits
(a) How a photosystem harvests light
(b) Structure of a photosystem
412 photosystems
- Photosystem I (older)
- Absorbs energy at 700 nm wavelength
- Generates NADPH
- Photosystem II (newer)
- Absorbs energy at 680 nm wavelength
- Splits water (releases oxygen)
- Generates ATP
- 2 systems work together to absorb more energy
42NADP
- Nicotinamide Adenine Dinucleotide Phosphate
- Coenzyme
- Electron carrier
- Reduced during light-dependent reactions
- Used later to reduce carbon
- Carbon dioxide forms organic molecules
- Photosynthesis is a redox reaction
43Photophosphorylation
- Addition of phosphate group to ADP
- Light energy
44Photosynthesis
- Occurs in 3 stages
- 1. Capturing energy from sun
- 2. Energy makes ATP
- Reducing power in NADPH
- 3. ATP NADPH
- Power synthesis of organic molecules
45Photosynthesis
- Light dependent reactions
- First 2 steps of photosynthesis
- Presence of light
- Light-independent reactions
- Formation of organic molecules
- Calvin cycle
- Can occur /- light
46Photosynthesis
- 1. Chloroplasts
- 2. Light-dependent reactions
- Suns energy makes NADPH ATP
- 3. Light-independent reactions
- ATP NADPH
- CO2 into organic molecules
47Fig. 10-5-4
H2O
CO2
Light
NADP
ADP
P
i
Calvin Cycle
Light Reactions
ATP
NADPH
Chloroplast
CH2O (sugar)
O2
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49Photosynthesis (Process)
- Light dependent reactions
- Linear electron flow
- Energy transfer
- Thylakoid membranes
50Light dependent reactions
- Photosystem II (680 nm)
- Light is captured by pigments
- Excites an electron (unstable)
- Energy is transferred to reaction center (special
chlorophyll) - Passes excited electron to an acceptor molecule
51Light dependent reactions
- PS II is oxidized
- Water splits (enzyme)
- Water donates an electron to chlorophyll
- Reduces PS II
- Oxygen (O2) is released with 2 protons (H)
52Light dependent reactions
- Electron is transported to PS I (700 nm)
- Electron is passed along proteins in the membrane
(ETC) - Protons are transported across the membrane
- Protons flow back across the membrane through
ATP synthase - Generate ATP
53Light dependent reactions
- At the same time PS I received light energy
- Excites an electron
- Primary acceptor accepts the electron
- PS I is excited
- Electron from PS II is passed to PS I
- Reduces the PS I
54Light dependent reactions
- PS I excited electron is passed to a second ETC
- Ferredoxin protein
- NADP reductase catalyzes the transfer of the
electron to NADP - Makes NADPH
55Fig. 10-13-5
Electron transport chain
Primary acceptor
Primary acceptor
4
7
Electron transport chain
Fd
Pq
e
2
e
8
e
e
NADP H
H2O
Cytochrome complex
2 H
NADP reductase
3
NADPH
O2
1/2
Pc
e
e
P700
5
P680
Light
Light
1
6
6
ATP
Pigment molecules
Photosystem I (PS I)
Photosystem II (PS II)
56Fig. 10-UN1
H2O
CO2
Primary acceptor
Electron transport chain
Primary acceptor
Fd
Electron transport chain
NADP H
H2O
Pq
NADP reductase
O2
NADPH
Cytochrome complex
Pc
Photosystem I
ATP
Photosystem II
O2
57Enhancement effect
58Enhancement effect
59Fig. 10-17
STROMA (low H concentration)
Cytochrome complex
Photosystem I
Photosystem II
Light
4 H
NADP reductase
Light
3
Fd
NADP H
NADPH
Pq
Pc
e
2
e
H2O
O2
1/2
1
THYLAKOID SPACE (high H concentration)
4 H
2 H
To Calvin Cycle
Thylakoid membrane
ATP synthase
STROMA (low H concentration)
ADP
ATP
P
i
H
60Fig. 10-16
Mitochondrion
Chloroplast
CHLOROPLAST STRUCTURE
MITOCHONDRION STRUCTURE
H
Diffusion
Intermembrane space
Thylakoid space
Electron transport chain
Inner membrane
Thylakoid membrane
ATP synthase
Stroma
Matrix
Key
ADP P
i
ATP
Higher H
H
Lower H
61Photosystems
- Noncyclic photophosphorylation
- 2 systems work in series
- Produce NADPH ATP
- Replaces electrons from splitting water
- System II (splits water)works first then I (NADPH)
62Photosystems
- When more ATP is needed
- Plant changes direction
- Electron used to make NADPH in PS I is directed
to make ATP
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65Calvin Cycle
- Named for Melvin Calvin
- Cyclic because it regenerates its starting
material - C3 photosynthesis
- First organic compound has 3 carbons
66Calvin cycle
- Combines CO2 to make sugar
- Using energy from ATP
- Using reducing power from NADPH
- Occurs in stroma of chloroplast
67Calvin Cycle
- Consists of three parts
- 1. Fixation of carbon dioxide
- 2. Reduction-forms G3P (glyceraldehyde
3-phosphate) - 3. Regeneration of RuBP (ribulose 1, 5
bisphosphate)
68Calvin Cycle
- 3 cycles
- 3 CO2 molecules
- 1 molecule of G3P
- 6 NADPH
- 9 ATP
69Fixation of carbon
- CO2 combines with
- Ribulose 1, 5 bisphosphate (RuBP)
- Temporary 6 carbon intermediate
- Splits-forms 2- three carbon molecules
- 3-phosphoglycerate (PGA)
- Large enzyme that catalyses reaction
- (Rubisco) Ribulose bisphosphate
carboxylase/oxygenase
70Reduction
- Phosphate is added to 3-phosphoglycerate
- 1,3 Bisphosphoglycerate
- NADPH reduces the molecule
- Glyceraldehyde 3-phosphate (G3P)
71Regeneration
- 5 molecules of G3P are rearranged to make 3 RuBP
- Uses 3 more ATP
72Fig. 10-18-3
(Entering one at a time)
Input
3
CO2
Phase 1 Carbon fixation
Rubisco
3
P
P
Short-lived intermediate
6
P
3
P
P
Ribulose bisphosphate (RuBP)
3-Phosphoglycerate
ATP
6
6 ADP
3 ADP
Calvin Cycle
P
6
P
3
ATP
1,3-Bisphosphoglycerate
6
NADPH
Phase 3 Regeneration of the CO2 acceptor (RuBP)
6 NADP
P
6
i
P
5
G3P
P
6
Glyceraldehyde-3-phosphate (G3P)
Phase 2 Reduction
1
P
Glucose and other organic compounds
Output
G3P (a sugar)
73Fig. 10-UN2
3 CO2
Carbon fixation
3 ? 5C
6 ? 3C
Calvin Cycle
Regeneration of CO2 acceptor
5 ? 3C
Reduction
1 G3P (3C)
74Calvin Cycle
- 3 CO2 enter cycle combine with RuBP
- Generates 3 molecules more of RuBP one G3P
(glyceraldehyde 3-phosphate) - G3P can be made into glucose other sugars
75Calvin Cycle
- Enzyme mediated
- 5 of these enzymes need light to be more
efficient - Net reaction
- 3CO2 9 ATP 6NADPH ?
- G3P 8Pi 9ADP 6NADP
76G3P
- G3P
- Converted to fructose 6-phosphate (reverse of
glycolysis) - Made into sucrose
- Happens in cytoplasm
- Intense photosynthesis
- G3P levels rise so much some is converted to
starch
77Fig. 10-21
H2O
CO2
Light
NADP
ADP
P
i
Light Reactions Photosystem II Electron
transport chain Photosystem I Electron
transport chain
RuBP
3-Phosphoglycerate
Calvin Cycle
ATP
G3P
Starch (storage)
NADPH
Chloroplast
O2
Sucrose (export)
78Summary
- Light reactions
- Thylakoids
- Use Suns energy
- Make ATP NADPH
- Split water make oxygen
79Summary
- Dark reactions
- Stroma
- Use ATP NADPH
- Make G3P
- Regenerate
- ADP, Inorganic P, and NADP
80O2
CO2
H2O
Sucrose (export)
Mesophyll cell
Chloroplast
H2O
CO2
Light
NADP
ADP
3-Phosphoglycerate
LIGHT REACTIONSPhotosystem II Electron
transport chain
CALVIN CYCLE
P
RuBP
i
ATP
G3P
Photosystem I Electron transport chain
NADPH
Starch (storage)
Sucrose (export)
O2
H2O
81MAKE CONNECTIONS
Movement Across Cell Membranes (Chapter 7)
Energy Transformations in the Cell Photosynthesis
and Cellular Respiration (Chapters 810)
Flow of Genetic Information in the Cell DNA ?
RNA ? Protein (Chapters 57)
The Working Cell
DNA
1
Nucleus
mRNA
Nuclear pore
2
Rough endoplasmic reticulum (ER)
Protein
Protein in vesicle
3
mRNA
Vacuole
Ribosome
4
Vesicle forming
Photosynthesis in chloroplast
7
CO2
Golgi apparatus
H2O
Protein
ATP
Transport pump
Organic molecules
8
Plasma membrane
ATP
5
Cellular respiration in mitochondrion
ATP
O2
ATP
9
Cell wall
O2
CO2
H2O
82Photorespiration
- Rubisco oxidizes RuBP (starting molecules of
Calvin cycle) - Oxygen is incorporated into RuBP
- Undergoes reactions that release CO2
- CO2 O2 compete for same sight on the enzyme
- Under conditions greater than the optimal 250C
this process occurs more readily
83Photorespiration
- Hot
- Stoma in leaf close to avoid loosing water
- Carbon dioxide cannot come in
- Oxygen builds up inside
- Carbon dioxide is released
- G3P is not produced
84C4 Photosynthesis
- Process to avoid loosing carbon dioxide
- Plant fixes carbon dioxide into a 4 carbon
molecule (oxaloacetate) - PEP carboxylase (enzyme)
- Oxaloacetate is converted to malate
- Then taken to stroma for Calvin cycle
- Sugarcane and corn
85C4 leaf anatomy
The C4 pathway
Mesophyll cell
Mesophyll cell
Photo- synthetic cells of C4 plant leaf
CO2
PEP carboxylase
Bundle- sheath cell
Oxaloacetate (4C)
PEP (3C)
ADP
Vein (vascular tissue)
Malate (4C)
ATP
Pyruvate(3C)
CO2
Bundle- sheath cell
Stoma
Calvin Cycle
Sugar
Vascular tissue
86CAM
- Process to prevent loss of CO2
- Plants in dry hot regions (cacti)
- Reverse what most plants do
- Open stoma at night
- Allows CO2to come in water to leave
- Close them during the day.
87CAM
- Carbon fix CO2 at night into 4 carbon chains
(organic acids) - Use the Calvin cycle during the day.
88Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
CO2
Mesophyll cell
Night
CO2 incorporated into four-carbon organic
acids (carbon fixation)
1
Organic acid
Organic acid
Bundle- sheath cell
Day
CO2
CO2
Organic acids release CO2 to Calvin cycle
2
Calvin Cycle
Calvin Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
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