Bio 226: Cell and Molecular Biology - PowerPoint PPT Presentation

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Bio 226: Cell and Molecular Biology

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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 – PowerPoint PPT presentation

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Title: Bio 226: Cell and Molecular Biology


1
Photosynthesis 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

3
Light Rxns 3 stages 1) Catching a photon
(primary photoevent) 2) ETS 3) ATP synthesis by
chemiosmosis
4
Light Reactions 1) Primary photoevent pigment
absorbs a photon
5
4 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
6
4 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
7
Photosystems Pigments are bound to proteins
arranged in thylakoids in photosystems arrays
that channel energy absorbed by any pigment to
rxn center chlorophylls
8
Photosystems 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
9
Photosystems 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
10
Photosystems 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
11
Photosystems Each may have associated LHC (light
harvesting complex) (LHC can diffuse within
membrane) PSI has LHCI 100 chl a, a few chl b
carotenoids
12
Photosystems 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
13
Photosystems 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
14
Photosystems 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
15
Photosystems Dinoflagellates absorb light with
peridininchlorophyll a-proteins mix of
proteins the carotenoid peridinin that absorb _at_
480 channel to Chl a
16
Photosystems Result in very different absorption
spectra
17
Photosystems PSI performs cyclic
photophosphorylation Absorbs photon transfers
energy to P700
18
cyclic photophosphorylation Absorbs photon
transfers energy to P700 transfers excited e-
from P700 to fd
19
cyclic 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
20
cyclic 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
21
Cyclic 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
22
Cyclic photophosphorylation first step is from
P700 to A0 (another chlorophyll a) charge
separation prevents e- from returning to ground
state true photoreaction
23
Cyclic photophosphorylation first step is from
P700 to A0 (another chlorophyll a) next transfer
e- to A1 (a phylloquinone) next 3 Fe/S proteins
24
Cyclic 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)

27
Cyclic photophosphorylation 3) Fe/S reduces
plastocyanin via cyt f cyt b6 reduces PQ to form
PQ-
28
Cyclic photophosphorylation 4) repeat process,
Fe/S reduces plastocyanin via cyt f cyt b6
reduces PQ- to form PQH2
29
Cyclic 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)
30
Cyclic photophosphorylation 5) PC (Cu) diffuses
to PSI, where it reduces an oxidized P700
31
Cyclic photophosphorylation energetics light
adds its energy to e- -gt excited state Eo' P700
0.48 V Eo' P700 -1.3 V
32
Cyclic 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
33
Cyclic 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
34
Cyclic 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
35
Cyclic 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
36
Cyclic photophosphorylation e- left in excited
state returns in ground state Energy pumped H
37
Cyclic photophosphorylation Limitations Only
makes ATP
38
Cyclic photophosphorylation Limitations Only
makes ATP Does not supply electrons for
biosynthesis no reducing power
39
Photosystems PSI performs cyclic
photophosphorylation Makes ATP but not NADPH
exact mech for PQ reduction unclear, but PQ
pumps H
40
Photosystem II Evolved to provide reducing
power -gt added to PSI
41
Photosystem II Evolved to provide reducing
power Added to PSI rxn center absorbs 680 nm (cf
700 nm)
42
Photosystem 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)
43
Photosystem 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)
44
Photosystem 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
45
PSI 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
46
PSI 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
47
PSI 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
48
PSI and PSII work together in the Z-scheme 1)
PSI reduces NADP
49
PSI and PSII work together in the Z-scheme 1)
PSI reduces NADP e- are replaced by PSII
50
PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI
51
PSI and PSII work together in the Z-scheme 2)
PSII gives excited e- to ETS ending at PSI Each
e- drives cyt b6/f
52
PSI 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
53
PSI 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
54
PSI 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
56
Z-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

60
Physical organization of Z-scheme D1 D2 bind
P680 all e- carriers Synechoccous elongatus
associates phycobilisomes cf LHCII with PSII
61
Physical 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

63
Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone lipid similar to
ubiquinone headgroup alternates between
quinone quinol
64
Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone lipid similar to
ubiquinone headgroup alternates between
quinone quinol Carries 2 e- 2 H
65
Physical 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
66
Physical organization of Z-scheme 2 mobile
carriers 1) plastoquinone 2) plastocyanin (PC)
peripheral membrane protein of thylakoid lumen
67
Physical organization of Z-scheme 2) plastocyanin
(PC) peripheral membrane protein of thylakoid
lumen Cu is alternately oxidized
reduced carries 1 e- 1 H
68
Physical 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
69
Physical 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
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