PHOTOSYNTHESIS
description
Transcript of PHOTOSYNTHESIS
PHOTOSYNTHESIS
1. Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes.
2. These organisms feed not only themselves but also the entire living world.
LE 10-2
Plants
Unicellular protist
Multicellular algae Cyanobacteria
Purple sulfurbacteria
10 µm
1.5 µm
40 µm
3. Photosynthesis occurs in the chloroplasts ofgreen plants.
4. General equation:6H2O + 6CO2 ----------------- C6H12O6 + 6O2Chlorophyll
Light
5. Recall that the chloroplast has a double outer membrane, a liquid stroma and an extensive inner membrane system made ofthylakoids that occur in stacks (grana).
LE 10-3
Leaf cross sectionVein
Mesophyll
Stomata CO2O2
Mesophyll cellChloroplast
5 µm
Outermembrane
Intermembranespace
Innermembrane
Thylakoidspace
Thylakoid
GranumStroma
1 µm
6. There are 2 basic parts of photosynthesis:light-dependent and light-independentreactions.
LE 10-5_1
H2O
LIGHTREACTIONS
Chloroplast
Light
LE 10-5_2
H2O
LIGHTREACTIONS
Chloroplast
Light
ATP
NADPH
O2
LE 10-5_3
H2O
LIGHTREACTIONS
Chloroplast
Light
ATP
NADPH
O2
NADP+
CO2
ADPP+ i
CALVINCYCLE
[CH2O](sugar)
7. Embedded in the thylakoid membranes arethe photosystems (PS I and PSII).
9. Both types of photosystems are involved innoncyclic photophosphorylation. Only PSIis involved in cyclic photophosphorylation.
8. Photosystem = light harvesting complex +a reaction center. A reaction center = a chlorophyll molecule and a protein.
LE 10-12
Thylakoid
Photon
Light-harvestingcomplexes
Photosystem
Reactioncenter
STROMA
Primary electronacceptor
e–
Transferof energy
Specialchlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
Th
ylak
oid
mem
bra
ne
-Each photosystem can absorb a different wavelength of light. PSI absorbs the far-red part of the spectrum best. PSII absorbs the not-so-far red part of the spectrum.
10. Noncyclic photophosphorylation a. Light energizes chlorophyll in PS II exciting
an electron (e-) which moves to the electrontransport chain. Now we see how photosynthesis uses light energy to get started.
QuickTime™ and a decompressor
are needed to see this picture.
LE 10-13_1
LightP680
e–
Photosystem II(PS II)
Primaryacceptor
[CH2O] (sugar)
NADPH
ATP
ADP
CALVINCYCLE
LIGHTREACTIONS
NADP+
Light
H2O CO2
En
erg
y o
f el
ectr
on
sO2
b. The chlorophyll that was oxidized (last slide) is reduced by the photolysis (breakdown) of water.
H2O 2 e- + 2 H+ 1 oxygen
These e- replace the ones lost from thechlorophyll.
•Now we see why photosynthesis requires water and why it releases oxygen!
LE 10-13_2
LightP680
e–
Photosystem II(PS II)
Primaryacceptor
[CH2O] (sugar)
NADPH
ATP
ADP
CALVINCYCLE
LIGHTREACTIONS
NADP+
Light
H2O CO2
En
erg
y o
f el
ectr
on
sO2
e–
e–
+2 H+
H2O
O21/2
c. Those protons (2 H+)from the split water are added to the lumen. Just like in cellular respiration, we are building a proton gradient. The free energy of the e- is used to power proton pumps transporting protons from the stroma to the lumen.
LE 10-16
MITOCHONDRIONSTRUCTURE
Intermembranespace
MembraneElectrontransport
chain
Mitochondrion Chloroplast
CHLOROPLASTSTRUCTURE
Thylakoidspace
Stroma
ATP
Matrix
ATPsynthase
Key
H+ Diffusion
ADP + P
H+
i
Higher [H+]
Lower [H+]
d. Next, more light energizes electrons in PS I. These excited e- move to the electron transport system.
e. The e- and the free protons in the stroma are used to reduce NADP+ to NADPH.
LE 10-13_3
LightP680
e–
Photosystem II(PS II)
Primaryacceptor
[CH2O] (sugar)
NADPH
ATP
ADP
CALVINCYCLE
LIGHTREACTIONS
NADP+
Light
H2O CO2
En
erg
y o
f el
ectr
on
sO2
e–
e–
+2 H+
H2O
O21/2
Pq
Cytochromecomplex
Electron transport chain
Pc
ATP
LE 10-13_4
LightP680
e–
Photosystem II(PS II)
Primaryacceptor
[CH2O] (sugar)
NADPH
ATP
ADP
CALVINCYCLE
LIGHTREACTIONS
NADP+
Light
H2O CO2
En
erg
y o
f el
ectr
on
s
O2
e–
e–
+2 H+
H2O
O21/2
Pq
Cytochromecomplex
Electron transport chain
Pc
ATP
P700
e–
Primaryacceptor
Photosystem I(PS I)
Light
LE 10-13_5
LightP680
e–
Photosystem II(PS II)
Primaryacceptor
[CH2O] (sugar)
NADPH
ATP
ADPCALVINCYCLE
LIGHTREACTIONS
NADP+
Light
H2O CO2E
ner
gy
of
elec
tro
ns
O2
e–
e–
+2 H+
H2O
O21/2
Pq
Cytochromecomplex
Electron transport chain
Pc
ATP
P700
e–
Primaryacceptor
Photosystem I(PS I)
e–e–
ElectronTransportchain
NADP+
reductase
Fd
NADP+
NADPH
+ H+
+ 2 H+
Light
LE 10-14
ATP
Photosystem II
e–
e–
e–e–
MillmakesATP
e–
e–
e–
Ph
oto
n
Photosystem I
Ph
oto
n
NADPH
-Our products from noncyclic photophosphorylation are .. .
ATP and NADPH
-These products will be used in the dark reactions of photosynthesis.
11. Cyclic photophosphorylation occurs in PS I. It is not as common as noncyclic.
Excited e- in PS I are cycled back and forthto the electron transport system. Their energyis used to pump protons in the lumen.
-The only product of cyclic is ATP. Thedark cycle use lots of ATP
LE 10-15
Photosystem I
Photosystem II ATP
Pc
Fd
Cytochromecomplex
Pq
Primaryacceptor
Fd
NADP+
reductase
NADP+
NADPH
Primaryacceptor
-For both cyclic and nocyclic:
A proton gradient is then established. The protons pass down the gradient andgo through ATP synthases embeddedin the membrane. Their energy hereis used to join ADP and Pi to formATP (This process is calledchemiosmosis).
LE 10-17
STROMA(Low H+ concentration)
Light
Photosystem IICytochrome
complex
2 H+
Light
Photosystem I
NADP+
reductase
Fd
PcPq
H2O O2
+2 H+
1/2
2 H+
NADP+ + 2H+
+ H+NADPH
ToCalvincycle
THYLAKOID SPACE(High H+ concentration)
STROMA(Low H+ concentration)
Thylakoidmembrane ATP
synthase
ATP
ADP+P
H+i
[CH2O] (sugar)O2
NADPH
ATP
ADP
NADP+
CO2H2O
LIGHTREACTIONS
CALVINCYCLE
Light
12. Light Independent Reactions – A.K.A. –THE DARK REACTIONS!
A.The light dependent reactions producedATP’s and NADPH’s. These are used to power the dark reactions.
B. The dark reactions occur in the stroma. Theyoccur in a cycle called the Calvin cycle.
C. The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle.
D. The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH.
E. Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P)
F. For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2.
G. The Calvin cycle has three phases:
*Carbon fixation (catalyzed by rubisco)
*Reduction
*Regeneration of the CO2 acceptor (RuBP)
LE 10-18_1
[CH2O] (sugar)O2
NADPH
ATP
ADP
NADP+
CO2H2O
LIGHTREACTIONS
CALVINCYCLE
LightInput
3
CO2
(Entering oneat a time)
Rubisco
3 P P
Short-livedintermediate
Phase 1: Carbon fixation
6 P
3-Phosphoglycerate6 ATP
6 ADP
CALVINCYCLE
3 P P
Ribulose bisphosphate(RuBP)
LE 10-18_2
[CH2O] (sugar)O2
NADPH
ATP
ADP
NADP+
CO2H2O
LIGHTREACTIONS
CALVINCYCLE
Light Input
CO2
(Entering oneat a time)
Rubisco
3 P P
Short-livedintermediate
Phase 1: Carbon fixation
6 P
3-Phosphoglycerate6 ATP
6 ADP
CALVINCYCLE
3
P P
Ribulose bisphosphate(RuBP)
3
6 NADP+
6
6 NADPH
P i
6 P
1,3-BisphosphoglycerateP
6 P
Glyceraldehyde-3-phosphate(G3P)
P1
G3P(a sugar)Output
Phase 2:Reduction
Glucose andother organiccompounds
LE 10-18_3
[CH2O] (sugar)O2
NADPH
ATP
ADP
NADP+
CO2H2O
LIGHTREACTIONS
CALVINCYCLE
Light Input
CO2
(Entering oneat a time)
Rubisco
3 P P
Short-livedintermediate
Phase 1: Carbon fixation
6 P
3-Phosphoglycerate6 ATP
6 ADP
CALVINCYCLE
3
P P
Ribulose bisphosphate(RuBP)
3
6 NADP+
6
6 NADPH
P i
6 P
1,3-BisphosphoglycerateP
6 P
Glyceraldehyde-3-phosphate(G3P)
P1
G3P(a sugar)Output
Phase 2:Reduction
Glucose andother organiccompounds
3
3 ADP
ATP
Phase 3:Regeneration ofthe CO2 acceptor(RuBP) P5
G3P
-The majority of the 3-carbon molecules are actually recycled to keep the Calvin cyclegoing.
The G3P are used to make sugars. Thesesugars are stored or used by the mitochondriain the process of cellular respiration.