Title: Bio 226: Cell and Molecular Biology
1Photosynthesis 1) Light rxns use light to pump
H use ? pH to make ATP by chemiosmosis 2)
Light-independent (dark) rxns use ATP NADPH
from light rxns to make organics only link each
provides substrates needed by the other
2- Important structural features of chloroplasts
- 1) outer envelope
- 2) inner envelope
- 3) thylakoids stromal membranes most fluid
known - PSI ATP synthase are on outside
- PSII is on inside of grana
3Light Rxns 3 stages 1) Catching a photon
(primary photoevent) 2) ETS 3) ATP synthesis by
chemiosmosis
4Light Reactions 1) Primary photoevent pigment
absorbs a photon
54 fates for excited e- 1) fluorescence 2)
transfer to another molecule 3) Returns to ground
state dumping energy as heat 4) energy is
transferred by inductive resonance excited e-
vibrates and induces adjacent e- to vibrate at
same frequency
64 fates for excited e- 4) energy is transferred
by inductive resonance excited e- vibrates and
induces adjacent e- to vibrate at same
frequency Only energy is transferred e- returns
to ground state
7Photosystems Pigments are bound to proteins
arranged in thylakoids in photosystems arrays
that channel energy absorbed by any pigment to
rxn center chlorophylls
8Photosystems Pigments are bound to proteins
arranged in thylakoids in photosystems arrays
that channel energy absorbed by any pigment to
rxn center chls Need 2500 chlorophyll to make 1 O2
9Photosystems Arrays that channel energy absorbed
by any pigment to rxn center chls 2 photosystems
PSI PSII PSI rxn center chl a dimer absorbs
700 nm P700
10Photosystems Arrays that channel energy absorbed
by any pigment to rxn center chls 2 photosystems
PSI PSII PSI rxn center chl a dimer absorbs
700 nm P700 PSII rxn center chl a
dimer absorbs 680 nm P680
11Photosystems Each may have associated LHC (light
harvesting complex) (LHC can diffuse within
membrane) PSI has LHCI 100 chl a, a few chl b
carotenoids
12Photosystems Each may have associated LHC (light
harvesting complex) (LHC can diffuse within
membrane) PSI has LHCI 100 chl a, a few chl b
carotenoids PSII has LHCII 250 chl a, many chl
b carotenoids Proteins of LHCI LHCII also
differ
13Photosystems Cyanobacteria red algae associate
phycobilisomes cf LHCII with PSII proteins that
absorb light pass energy to rxn center
chl Absorb 500-650 nm PE phycoerythrin Absorbs
500 570 PC phycocyanin Absorbs 620 AP
allophycocyanin Absorbs 650
14Photosystems green sulfur bacteria absorb light
with chlorosomes mix of proteins, carotenoids
and Bact Chl c that channel light to Bact Chl a
(795 nm) then rxn center p840
15Photosystems Dinoflagellates absorb light with
peridininchlorophyll a-proteins mix of
proteins the carotenoid peridinin that absorb _at_
480 channel to Chl a
16Photosystems Result in very different absorption
spectra
17Photosystems PSI performs cyclic
photophosphorylation Absorbs photon transfers
energy to P700
18cyclic photophosphorylation Absorbs photon
transfers energy to P700 transfers excited e-
from P700 to fd
19cyclic photophosphorylation Absorbs photon
transfers energy to P700 transfers excited e-
from P700 to fd fd returns e- to P700 via PQ,
cyt b6/f PC
20cyclic photophosphorylation Absorbs photon
transfers energy to P700 transfers excited e-
from P700 to fd fd returns e- to P700 via PQ, cyt
b6/f PC Cyt b6/f pumps H
21Cyclic Photophosphorylation Transfers excited e-
from P700 to fd Fd returns e- to P700 via cyt
b6-f PC Cyt b6-f pumps H Use PMF to make ATP
22Cyclic photophosphorylation first step is from
P700 to A0 (another chlorophyll a) charge
separation prevents e- from returning to ground
state true photoreaction
23Cyclic photophosphorylation first step is from
P700 to A0 (another chlorophyll a) next transfer
e- to A1 (a phylloquinone) next 3 Fe/S proteins
24Cyclic photophosphorylation first step is from
P700 to A0 (another chlorophyll a) next transfer
e- to A1 (a phylloquinone) next 3 Fe/S
proteins finally ferredoxin
25- Cyclic photophosphorylation
- Ferredoxin branchpoint in cyclic PS FD reduces
PQ
26- Cyclic photophosphorylation
- Ferredoxin reduces PQ
- PQH2 diffuses to cyt b6/f
- 2) PQH2 reduces cyt b6 and Fe/S, releases H in
lumen - since H came from stroma, transports 2 H across
membrane (Q cycle)
27Cyclic photophosphorylation 3) Fe/S reduces
plastocyanin via cyt f cyt b6 reduces PQ to form
PQ-
28Cyclic photophosphorylation 4) repeat process,
Fe/S reduces plastocyanin via cyt f cyt b6
reduces PQ- to form PQH2
29Cyclic photophosphorylation 4) repeat process,
Fe/S reduces plastocyanin via cyt f cyt b6
reduces PQ- to form PQH2 Pump 4H from stroma to
lumen at each cycle (per net PQH2)
30Cyclic photophosphorylation 5) PC (Cu) diffuses
to PSI, where it reduces an oxidized P700
31Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V
32Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V Eo' fd - 0.42 V
33Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V Eo' fd - 0.42 V Eo'
cyt b6/f 0.3V
34Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V Eo' fd - 0.42 V Eo'
cyt b6/f 0.3V Eo' PC 0.36V
35Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V Eo' fd - 0.42 V Eo'
cyt b6/f 0.3V Eo' PC 0.36V e- left in
excited state returns in ground state
36Cyclic photophosphorylation e- left in excited
state returns in ground state Energy pumped H
37Cyclic photophosphorylation Limitations Only
makes ATP
38Cyclic photophosphorylation Limitations Only
makes ATP Does not supply electrons for
biosynthesis no reducing power
39Photosystems PSI performs cyclic
photophosphorylation Makes ATP but not NADPH
exact mech for PQ reduction unclear, but PQ
pumps H
40Photosystem II Evolved to provide reducing
power -gt added to PSI
41Photosystem II Evolved to provide reducing
power Added to PSI rxn center absorbs 680 nm (cf
700 nm)
42Photosystem II rxn center absorbs 680 nm (cf 700
nm) can oxidize H2O redox potential of P680 is
1.1 V (cf 0.82 V for H2O)
43Photosystem II rxn center absorbs 680 nm (cf 700
nm) can oxidize H2O redox potential of P680 is
1.1 V (cf 0.82 V for H2O) Use e- from H2O to
reduce NADP (the e- carrier used for catabolic
reactions)
44Photosystem II rxn center absorbs 680 nm (cf 700
nm) can oxidize H2O redox potential of P680 is
1.1 V (cf 0.82 V for H2O) Use e- from H2O to
reduce NADP (the e- carrier used for catabolic
reactions) use NADPH c.f. NADH to prevent
cross- contaminating catabolic anabolic pathways
45PSI and PSII work together in the Z-scheme -
a.k.a. non-cyclic photophosphorylation General
idea ? redox potential from H2O to NADP is so
great that must boost energy of H2O e- in 2
steps
46PSI and PSII work together in the Z-scheme
General idea ? redox potential from H2O to
NADP is so great that must boost energy of H2O
e- in 2 steps each step uses a photon
47PSI and PSII work together in the Z-scheme
General idea ? redox potential from H2O to
NADP is so great that must boost energy of H2O
e- in 2 steps each step uses a photon 2 steps 2
photosystems
48PSI and PSII work together in the Z-scheme 1)
PSI reduces NADP
49PSI and PSII work together in the Z-scheme 1)
PSI reduces NADP e- are replaced by PSII
50PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI
51PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI Each
e- drives cyt b6/f
52PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI Each
e- drives cyt b6/f Use PMF to make ATP
53PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI Each
e- drives cyt b6/f Use PMF to make ATP PSII
replaces e- from H2O forming O2
54PSI and PSII work together in the Z-scheme
Light absorbed by PS II makes ATP Light absorbed
by PS I makes reducing power
55 cyclic non-cyclic Ultimate e-
source None water O2 released? No yes Termin
al e- acceptor None NADP Form in which energy
is ATP ATP temporarily captured NADPH Photos
ystems required PSI PSI PSII
56Z-scheme energetics
57- Physical organization of Z-scheme
- PS II consists of P680 (a dimer of chl a)
- 30 other chl a a few carotenoids
- gt 20 proteins
- D1 D2 bind P680 all e- carriers
58- Physical organization of Z-scheme
- PSII has 2 groups of closely associated proteins
- 1) OEC (oxygen evolving complex)
- on lumen side, near rxn center
- Ca2, Cl- 4 Mn2
59- Physical organization of Z-scheme
- PSII also has two groups of closely associated
proteins - 1) OEC (oxygen evolving complex)
- on lumen side, near rxn center
- Ca2, Cl- 4 Mn2
- 2) variable numbers of LHCII complexes
60Physical organization of Z-scheme D1 D2 bind
P680 all e- carriers Synechoccous elongatus
associates phycobilisomes cf LHCII with PSII
61Physical organization of Z-scheme D1 D2 bind
P680 all e- carriers Synechoccous elongatus
associates phycobilisomes cf LHCII with PSII
62- Physical organization of Z-scheme
- 2 mobile carriers
- plastoquinone lipid similar
- to ubiquinone
-
63Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone lipid similar to
ubiquinone headgroup alternates between
quinone quinol
64Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone lipid similar to
ubiquinone headgroup alternates between
quinone quinol Carries 2 e- 2 H
65Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone hydrophobic molecule
like ubiquinone headgroup alternates between
quinone and quinol Carries 2 e- 2 H diffuses
within bilayer
66Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone 2) plastocyanin (PC)
peripheral membrane protein of thylakoid lumen
67Physical organization of Z-scheme 2) plastocyanin
(PC) peripheral membrane protein of thylakoid
lumen Cu is alternately oxidized
reduced carries 1 e- 1 H
68Physical organization of Z-scheme 3 protein
complexes (visible in EM of thylakoid) 1) PSI 2)
PSII 3) cytochrome b6/f 2 cytochromes an Fe/S
protein
69Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone 2) plastocyanin (PC) 3
protein complexes 1) PSI 2) PSII 3) cytochrome
b6/f ATP synthase (CF0-CF1 ATPase) is also
visible in E/M