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Transcript of Photosynthesis Chapter 10 Energy source Autotrophs: Producers Make own organic molecules...
Photosynthesis
Chapter 10
Energy source Autotrophs: Producers Make own organic molecules Heterotrophs: Consumers
Photosynthesis
Photosynthesis Organisms capture energy from
sunlight Build food molecules Rich in chemical energy 6CO2 + 12H2O ⇨
C6H12O6 + 6H2O + 6O2
Photosynthesis Captures only 1% of sun’s energy Provides energy for life
Photosynthesis
Leaf structure Stoma (Stomata) opening on leaf Exchange of gases. Chloroplasts Mesophyll layer of leaf
Chloroplasts Thylakoids: Internal membranes of chloroplasts Grana: Stacks of thylakoids Chlorophyll: Green pigment Captures light for photosynthesis Membranes of thylakoids
Chloroplasts Stroma: Semi-liquid substance Surrounds thylakoids Contain enzymes Make organic molecules from
carbon dioxide
Chloroplasts
Fig. 10-3b
1 µm
Thylakoidspace
Chloroplast
GranumIntermembranespace
Innermembrane
Outermembrane
Stroma
Thylakoid
Chloroplasts Photosystem: Cluster of photosynthetic pigments Membrane of thylakoids Each pigment captures energy Photosystem then gathers energy Energy makes ATP, NADPH &
organic molecules
NADP+
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
Photophosphorylation Addition of phosphate group to
ADP Light energy
Photosynthesis 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
Photosynthesis Light dependent reactions First 2 steps of photosynthesis Presence of light Light-independent reactions Formation of organic molecules Calvin cycle Can occur +/- light
Experimental history Jan Baptista van Helmont Plants made their own food Joseph Priestly Plants “restored” the air
Experimental history Jan Ingenhousz Sun’s energy split CO2 Carbon & Oxygen Oxygen was released into air Carbon combined with water Make carbohydrates
Experimental 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
Experimental history C.B. van Neil Looked at light in photosynthesis Studied photosynthesis in Bacteria
C.B. van NeilCO2 + 2H2S (CH2O) + H2O +
2S
CO2 + 2H2A (CH2O) + H2O + A2
CO2 + 2H2O (CH2O) + H2O + O2
C.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
CO2 + 2H2O (CH2O) + H2O + O2
CO2 + 2H2O (CH2O) + H2O + O2
Photosynthesis 1. Chloroplasts 2. Light-dependent reactions Sun’s energy makes NADPH & ATP 3. Light-independent reactions ATP & NADPH CO2 into organic molecules
Light
Fig. 10-5-4
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
CalvinCycle
CO2
[CH2O]
(sugar)
Sunlight UV light from sun Source of energy when life began UV light can cause mutations in
DNA Lead to skin cancer
Light Photon: Packets of energy UV light photons have greater
energy than visible light UV light has shorter wavelengths
Light Visible light Purple shorter wavelengths More energetic photons Red longer wavelengths Less energetic photons
Spectrum
Spectrum
Absorption Spectrums Photon of energy strikes a molecule Absorbed by the molecule or lost as
heat Depends on energy in photon
(wavelength) Depends on atom’s available
energy levels Specific for each molecule
Pigments Molecules Absorb energy in visible range Chlorophylls & Carotenoids Chlorophyll a & b Absorb photons in the blue-violet
& red light
Pigments Chlorophyll a main pigment of
photosynthesis Converts light energy to chemical
energy Chlorophyll b & carotenoids are
accessory pigments Capture light energy at different
wavelengths
Pigments
Pigments
Chlorophyll b
Carotenoids Chlorophyll a
Chlorophyll 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
Chlorophyll structure
D:\Chapter_10\A_PowerPoint_Lectures\10_Lecture_Presentation\10_07LightAndPigments_A.html
Carotenoids Two carbon rings attached by a
carbon chain Not as efficient as the Chlorophylls Beta carotene (helps eyes) Found in carrots and yellow
veggies
Photosystems Captures the light Located on surface of the
photosynthetic membrane Chlorophyll a molecules Accessory pigments (chlorophyll b
& carotenoids) Associated proteins
Photosystems Consists of 2 components 1. Antenna (light gathering)
complex 2. Reaction center
Photosystem 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
Photosystems 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)
Photosystem
Fig. 10-12
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
STROMA
e–
Pigmentmolecules
Photon
Transferof energy
Special pair ofchlorophyll amolecules
Th
yla
koid
me
mb
ran
e
Photosystem
Primaryelectronacceptor
Reaction-centercomplex
Light-harvestingcomplexes
2 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
Photosynthesis (Process) Light dependent reactions Linear electron flow Energy transfer Thylakoid membranes
Light 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
Light 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+)
Light 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
Light 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
Light 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
Pigmentmolecules
Light
P680
e–
Primaryacceptor
2
1
e–
e–
2 H+
O2
+3
H2O
1/2
4
Pq
Pc
Cytochromecomplex
Electron transport chain
5
ATP
Photosystem I(PS I)
Light
Primaryacceptor
e–
P700
6
Fd
Electron transport chain
NADP+
reductase
NADP+
+ H+
NADPH
8
7
e–
e–
6
Fig. 10-13-5
Photosystem II(PS II)
Fig. 10-UN1
CO2
NADP+
reductase
Photosystem II
H2O
O2
ATP
Pc
Cytochromecomplex
Primaryacceptor
Primaryacceptor
Photosystem I
NADP+
+ H+
Fd
NADPH
Electron transport
chain
Electron transport
chain
O2
H2O Pq
Enhancement effect
Enhancement effect
Fig. 10-17
Light
Fd
Cytochromecomplex
ADP +
i H+
ATPP
ATPsynthase
ToCalvinCycle
STROMA(low H+ concentration)
Thylakoidmembrane
THYLAKOID SPACE(high H+ concentration)
STROMA(low H+ concentration)
Photosystem II Photosystem I
4 H+
4 H+
Pq
Pc
LightNADP+
reductase
NADP+ + H+
NADPH
+2 H+
H2OO2
e–
e–
1/21
2
3
Fig. 10-16
Key
Mitochondrion Chloroplast
CHLOROPLASTSTRUCTURE
MITOCHONDRIONSTRUCTURE
Intermembranespace
Innermembrane
Electrontransport
chain
H+ Diffusion
Matrix
Higher [H+]Lower [H+]
Stroma
ATPsynthase
ADP + P i
H+ATP
Thylakoidspace
Thylakoidmembrane
Photosystems Noncyclic photophosphorylation 2 systems work in series Produce NADPH & ATP Replaces electrons from splitting
water System II (splits water)works first
then I (NADPH)
Photosystems When more ATP is needed Plant changes direction Electron used to make NADPH in
PS I is directed to make ATP
Calvin Cycle Named for Melvin Calvin Cyclic because it regenerates it’s
starting material C3 photosynthesis First organic compound has 3
carbons
Calvin cycle Combines CO2 to make sugar Using energy from ATP Using reducing power from NADPH Occurs in stroma of chloroplast
Calvin 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)
Calvin Cycle 3 cycles 3 CO2 molecules 1 molecule of G3P 6 NADPH 9 ATP
Fixation 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
Reduction Phosphate is added to 3-
phosphoglycerate 1,3 Bisphosphoglycerate NADPH reduces the molecule Glyceraldehyde 3-phosphate
(G3P)
Regeneration 5 molecules of G3P are rearranged
to make 3 RuBP Uses 3 more ATP
Fig. 10-18-3
Ribulose bisphosphate(RuBP)
3-Phosphoglycerate
Short-livedintermediate
Phase 1: Carbon fixation
(Entering oneat a time)
Rubisco
Input
CO2
P
3 6
3
3
P
PPP
ATP6
6 ADP
P P6
1,3-Bisphosphoglycerate
6
P
P6
66 NADP+
NADPH
i
Phase 2:Reduction
Glyceraldehyde-3-phosphate(G3P)
1 POutput G3P
(a sugar)
Glucose andother organiccompounds
CalvinCycle
3
3 ADP
ATP
5 P
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
G3P
Fig. 10-UN2
Regeneration ofCO2 acceptor
1 G3P (3C)
Reduction
Carbon fixation
3 CO2
CalvinCycle
6 3C
5 3C
3 5C
Calvin 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
Calvin Cycle Enzyme mediated 5 of these enzymes need light to
be more efficient Net reaction3CO2 + 9 ATP + 6NADPH ⇨
G3P + 8Pi + 9ADP + 6NADP+
G3P 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
Fig. 10-21
LightReactions:
Photosystem II Electron transport chain
Photosystem I Electron transport chain
CO2
NADP+
ADP
P i+
RuBP 3-Phosphoglycerate
CalvinCycle
G3PATP
NADPHStarch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
Photorespiration
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
Photorespiration Happens when 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
C4 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
CAM 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.
CAM Carbon fix CO2 at night into 4
carbon chains (organic acids) Use the Calvin cycle during the
day.
Fig. 10-20
CO2
Sugarcane
Mesophyllcell
CO2
C4
Bundle-sheathcell
Organic acidsrelease CO2 to Calvin cycle
CO2 incorporatedinto four-carbonorganic acids(carbon fixation)
Pineapple
Night
Day
CAM
SugarSugar
CalvinCycle
CalvinCycle
Organic acid Organic acid
(a) Spatial separation of steps (b) Temporal separation of steps
CO2 CO2
1
2