Download Archivo de clase Fotosíntesis 2003

Análisis del transporte de electrones en bioquímica

A
I1
X1

B
I2
C

D
X2
1) Los componentes A y D son el dador y el aceptor de electrones
exógenos, respectivamente.
2) Los componentes B y C de la cadena de transporte de electrones
se encuentran en baja concentración en la membrana.
3) ,  y  catalizan la transferencia de electrones
4) I1, I2 son inhibidores irreversibles de  y , respectivamente.
5) X1 y X2 son dadores de electrones exógenos.
Diferencia de potencial electroquímico de un ion
Para transferir un mol de ion Xn+ a través de una membrana
cuando :
- [Xn+]B  [Xn+]A , en ausencia de un campo eléctrico.
G = 2.3 * R * T * log([Xn+]B/[Xn+]A)
- [Xn+]B = [Xn+]A , en presencia de un campo eléctrico.
G = - n * F * 
donde F: constante de Faraday; n: carga del ion;  : potencial eléctrico
- [Xn+]B  [Xn+]A , en presencia de un campo eléctrico.
G = - n * F *  + 2.3 * R * T * log([Xn+]B/[Xn+]A)
Potencial electroquímico del protón
n = 1;
log ([H+]B / [H+]A) = - pH
H+ = - F *  - 2.3 * R* T * pH
Multiplicando por [1/(-F)]
H+/(-F) =  - [2.3 * R* T * (-F)] * pH
A 25 oC, [2.3 * R* T * F] = 0.6
H+/(-F) = p (potencial protón motriz)
p =  + 0.6 * pH
Energy transducing membranes. Chloroplast
CHEMIOSMOTIC THEORY
EXT
INT
AH
A
H+
+
H
B
Electron
transport
ADP + Pi
H+
ATP
BH
H+
H+-ATPase
Flujo reverso de electrones
AH
A
H+
ADP + Pi
H+
B
ATP
BH
H+
H+
H+
Uncoupled electron flow
AH
BH
A
H+
ADP + Pi
B
H+
ATP
H+
Uncoupler
How is ATP made?
Photophosphorylation
A H+ gradient in
chloroplasts makes ATP
via ATP-synthase.
pp. 540
H+-ATPase
membrana
Organisms within the biosphere exchange
molecules and energy
Energy of
sunlight
Light (via plants)
Useful chemical
bond energy
Autotrophs:
complex carbon,
glucose, amino acids
Phototrophs
& chemotrophs
CO2, H2O
Chemical oxidations
(via iron & sulfur
bacteria)
Heterotrophs
(e.g. some bacteria,
animals, humans)
Need 9 amino acids
& 15 vitamins from
outside sources
1st Law of Thermodynamics:
In any process, the total energy of the universe remains constant.
EXT
LIGHT
INT
AHH2O
A O2
H+
H+
B
NADP
ADP + Pi
+
H
ATP
BH
NADPH
H+
CARBON REACTIONS
OBJETIVOS
DE LA
CLASE
What is photosynthesis?
The process by which plants, algae, and some
bacteria use solar energy to drive the synthesis of
organic molecules (e.g. sugars, starch, etc.) from
carbon dioxide (CO2) and water (H2O).
Fig. 2.40 Molecular Biology of the Cell, 4th. Ed.
Estado de oxidación
CO2 : + 4
(CH2O) : (0)
1. How are plants able to convert
light energy into energy that can
be utilized by both themselves
and heterotrophs? What other
organisms can do this?
Photosynthesis reactions overview
General reaction 
CO2 + H2O
Carbon
dioxide
water
ATP, NADPH
(CH2O) + O2
Carbohydrate oxygen
(e.g. sucrose
or starch)
ATP, NADPH
Glucose synthesis  6 CO + 6 H O
C6H12O6 + 6 O2
2
2
carbon
water
glucose
oxygen
dioxide
Go’ = +686 kcal/mol
Photosynthesis involves two parts:
1. Light reactions (mediated by chlorophylls)
• use light to generate ATP, NADPH
2. Carbon reactions (also called, “Benson-Calvin cycle”)
• use ATP, NADPH, CO2 to synthesize sugar & starch
Occurs in: prokaryotes: bacteria, blue green algae, in cytoplasmic
membrane
eukaryotes: chloroplasts
Anatomy of a plant cell
Fig. 14.34. Molecular Biology of the Cell, 4th. Ed.
3 distinct membranes: outer, inner, thylakoid
3 separate internal compartments:
intermembrane, stroma, thylakoid lumen
carbon
reactions
An overview
of the
chloroplast
grana
light
reactions
Size = 5 m
pp. 529
Chlorophyll
pp. 530
Absorption process
Transition of an electron from the ground state
to an excited state provided:
A)
The energy gap [ground state  excited state]
matches the wavelength of light [E = h . c . -1]
B)
1) the e- moves in a straight line from the
ground state to the excited state
2) the translation charge across a chromophore
generates a transition electric dipole moment ()
3)  dictates the potential extent of absorption
quantified as the extintion coefficient 
S1
T1
P
So
InterSystem crossing
Photoproduct formation
Phosphorescence
Non-radiative deactivation
Radiative deactivation
Fluorescence
F = photons emitted / photons absorbed
F =
kR
kR + kNR + kISC + kPR
Deactivation processes of
the excited states
JCE 76: 1555 (1999)
Absorption and emission spectra of biphenyl
Chlorophyll. Absorption and emission spectra
E1 > E2  1 <  2
S1
S2
E2 = h *  2
E1 = h * 1
So
E3 = h *  3
E 1 > E 2 > E 3  1 <  2 <  3
Other pigments, antenna pigments, accessory
pigments
Reflects green
light; absorbs rest
Reflects yellow
light; absorbs rest
Reflects blue
light; absorbs
rest
Absorbance spectra of other pigments
 The combined absorption of all the chlorophylls
cover the entire spectrum of visible light.
A
N
T
E
N
A
h2
(Chl)
h1
reacción
D+
D
Centro
de
*
(Chl)
A
(Chl)+
A-
Interconversión de la clorofila
Structure of a photocenter
Electron transfer from accessory (i.e. antennae)
pigments to reaction center.
LIGHT
Antenna pigments
pp. 543
LUZ
D
D+
P

P+
P*
A
A-
Potenciales de óxido-reducción en el
centro de reacción
luz
P680
P680
[P680]+ + e
[P680]
[P680]+ + e
[P680]
[P680 ] : estado excitado;
Eo = 1.1 volt
Eo = - 0.7 volt
[P680] : estado basal
The “Z” scheme of photosynthesis
2 H2O + NADP+
O2 + NADPH
proton gradient
O2
pp. 538
Photosystem II
Thylakoid
membrane
Transfers electrons from water to plastiquinone (thus oxidizing it
to O2)
Generates proton (H+) gradient between thylakoid lumen and
stroma
pp. 534
Photosystem I
Thylakoid
membrane
Generates reduced ferredoxin (Fd)
PSI reduces NADP+ to NADPH (Fd-NADP-reductase).
pp. 537
Overview of electron flow through
thylakoid membrane proteins
The Cell: a molecular approach, fig. 10-22
Non-cyclic photophosphorylation
when PSII is inhibited
Cyclic photophosphorylation
Pseudocyclic photophosphorylation
EXT
LIGHT
INT
AHH2O
A O2
H+
H+
B
NADP
ADP + Pi
+
H
ATP
BH
NADPH
H+
CARBON REACTIONS
OBJETIVOS
DE LA
CLASE
Autotrophy
.
.
.
.
.
2 H+
H2O
PETS
O2
2 Fdox
S
S
FT R
2 Fdred
HS
SH
FT R
LIGHT
S
S
Trx
HS
SH
Trx
S S
En z
HS
The ferredoxinthioredoxin system
products
SH
Enz
substrates
RUBISCO
ADP
RUBISCO
ATP
CATALYTIC
CYCLE
RAinactive
RAactive
E-NH3+. RuBP
E-NH-CO2-. Mg2+.RuBP
CO2
O2
E-NH3+
Products
RuBP
RuBP
H+
E-NH2
CO2
E-NH-CO2H+
Mg2+
E-NH-CO2-
. Mg
2+
Residencia del DNA que codifica para
Rubisco
Organismo
LSU
SSU
Algas verdes,
plantas, Euglena
cloropl.
Núcleo
Algas rojas
cloropl.
cloropl.
Algas marrones
cloropl.
cloropl.
Dinoflagelados
Núcleo
X
L8S8
L2
RUBISCO
chloroplast
O2
glutamate
glycerate
-keto
glutarate
2
glycolate
NH4+
peroxisome
O2
2
serine
CO2
glycine
mitochondria
Carbon and nitrogen flow in the C2 oxidative
photorespiratory cycle
En la presentacion dice que es una planta C4. Documentos lindos
\facultad \para usar \photos\photosynth \general1 (carpeta) \ C4leaf
Plant performance
Plant
gH2O/g DM
C3
C4
CAM
450-950
250-350
50-55
Topt(oC)
15-25
30-40
ca. 35
Ton.DM/(Ha.yr)
20-25
35-40
low & variable
C4 photosynthesis. CO2 fixation
mesophyll
PEP + H2O + CO2
oxalacetate + Pi
oxalacetate + NADPH
malate + NADP+
PEPcarboxylase
NADP-malate
dehydrogenase
(bundle sheath)
C4 photosynthesis. CO2 assimilation
malate + NADP+
NADP-malic
enzyme
pyruvate + NADPH + CO2
mesophyll
pyruvate + Pi + ATP
PEP + AMP + PPi
Pyruvate
orthophosphate
dikinase
PPi + H2O
AMP + ATP
2 ADP
2 Pi pyrophosphatase
adenylate kinase
Cost of concentrating CO2 within the bundle
sheath cell
mesophyll
CO2 + 2 ATP + 2 H2O
CO2 + 2 ADP + 2 Pi
bundle sheath
C4
C3
Crassulacean acid metabolism
NIGHT
DAY
BIBLIOGRAFIA
PLANT PHYSIOLOGY, 3rd. Ed., L.Taiz & E.Zieger
Eds.,
Ch.7. Photosynthesis: the light reactions
Ch.8. Photosynthesis: carbon reactions
Sinauer Associates, Sunderland, MA. (2002)
BIOLOGIA CELULAR Y MOLECULAR, 4th. Ed.,
H.Lodish et al. Eds.,
Ch.16. Energética celular: glicólisis, oxidación
aeróbica, y fotosíntesis.
Editorial Panamericana, Buenos Aires. (2000)
BIOENERGETICS 2, D.G.Nicholls & S.J.Ferguson.
Academic Press, London. (1992)