Download Linear Electron Flow (PS I)

Linear
Electron
Flow
(PS
I)
• In
PS
I
(like
PS
II)
Ele
Primary
acceptor
1/
2 H+
+
O2
2
H2 O
e–
2
ctr
4
tra
nsp
on
Pq
cha
Cytochrome
complex
3
transferred
light
•
Primary
acceptor
ort
energy
excites
P700
e–
in
• loses
an
electron
Pc
e–
e–
to
acceptor
P700
5
P680
Light
1 Light
6
• P700+
ATP
Pigment
molecules
accepts
electron
•
Photosystem I
(PS I)
Photosystem II
(PS II)
from
PS
II
• via
the
electron
transport
chain
Linear
Electron
Flow
(PS
I)
•
Ele
Primary
acceptor
2 H+
+
1/ O
2 2
H2 O
e–
2
ctr
on
Pq
4
tra
ns
Primary
acceptor
port
cha
in
e–
Cytochrome
complex
3
Each
electron
•
E
tra lect
n ro
ch spo n
ain rt
•
Fd
e– –
e
8
NADP +
+ H+
NADP +
reductase
NADPH
Pc
e–
e–
falls
down
electron
transport
chain
7
•
P700
5
P680
Light
1 Light
from
primary
electron
acceptor
of
PS
I
6
to
ferredoxin
(Fd)
ATP
•
Pigment
molecules
electrons
then
transferred
to
NADP+
Photosystem I
(PS I)
Photosystem II
(PS II)
•
reduced
to
NADPH
•
Cyclic
Electron
Flow
• Cyclic
electron
flow
•
uses
only
photosystem
I
and
produces
ATP
• but
not
NADPH
• no
oxygen
released
•
generates
surplus
ATP
• meeKng
demand
for
Calvin
cycle
• Some
organisms
such
as
purple
sulfur
bacteria
•
have
PS
I
but
not
PS
II
• thought
to
have
evolved
before
linear
electron
flow
•
may
protect
cells
from
light‐induced
damage
goes
to
Calvin
cycle
Fig.
10‐15
Primary
acceptor
Primary
acceptor
Fd
Fd
Pq
NADP+
reductase
Cytochrome
complex
NADP+
+ H+
NADPH
Pc
Photosystem I
ATP
Photosystem II
What
Makes
the
Light
ReacKons
So
Important?
•
Two
acKons
of
great
consequence
take
place
in
the
light
reacKons
1. Water
is
split,
yielding
both
electrons
and
oxygen.
•
The
electrons
move
through
the
light
reacKons.
•
The
oxygen
is
what
organisms
such
as
ourselves
breathe
in.
2. The
electrons
that
are
derived
from
the
water
•
and
then
given
an
energy
boost
by
the
sun’s
rays
•
are
transferred
to
a
different
molecule:
the
iniKal
electron
acceptor
•
This
is
the
means
through
which
the
sun’s
energy
is
transferred
into
the
living
world
Importance
of
Light
ReacKons
• Also…
•
fall
of
electrons
through
the
electron
transport
chain
between
photosystems
II
and
I
• yields
energy
that
produces
ATP
• used
to
power
the
second
stage
of
photosynthesis
Light
ReacKons
PLAY
Light Reactions
STROMA
(low H+ concentration)
Cytochrome
Photosystem I
complex
Light
Photosystem II
4 H+
Light
Fd
NADP+
reductase
H 2O
THYLAKOID SPACE
(high H+ concentration)
e–
1
e–
1/
NADP+ + H+
Pc
2
2
3
NADPH
Pq
O2
+2
H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP
+
Pi
ATP
H+
The
Calvin
Cycle
• Carbon
dioxide
from
the
atmosphere
•
Combined
with
a
sugar
• RuBP
(Ribulose‐1,5‐bisphosphate)
• RuBisCo
(Ribulose‐1,5‐bisphosphate
carboxylase/oxygenase)
• Enzyme
that
catalyzes
RuBP
and
CO2
• resulKng
compound
•
energized
with
addiKon
of
electrons
•
Makes
3‐carbon
sugars
• supplied
by
light
reacKons
• Later
combined
into
carbohydrates
The
Calvin
Cycle
• G3P
•
Glyceraldehyde
3‐phosphate
•
High‐energy
sugar
•
The
result
of
the
Calvin
cycle
•
Final
product
of
photosynthesis
•
Can
be
used
for
energy
or
plant
structure
The
Calvin
Cycle
Input
3
CO2
(Entering one
at a time)
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 P
i
5
P
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Phase 2:
Reduction
Glucose and
other organic
compounds
The
Calvin
Cycle
• All
these
steps
are
powered
by
ATP
produced
in
the
light
reacKons
Summary
PhotorespiraKon
and
the
C4
Pathway
• In
plants
the
enzyme
rubisco
frequently
binds
with
oxygen
rather
than
with
carbon
dioxide
•
• a
process
called
photorespiraKon
that
undercuts
photosynthesis.
PhotorespiraKon
•
problem
increases
as
temperature
rises
•
because
as
plants
close
their
stomata
to
keep
in
moisture
•
they
also
keep
out
CO 2
•
increasing
likelihood
that
rubisco
will
bind
with
oxygen
•
Rubisco‐oxygen
then
metabolized
•
EvoluKonary
relic?
•
Releasing
carbon
dioxide
•
Atmospheric
O2
low
when
rubisco
evolved
•
May
be
protecKve
•
Against
damage
from
buildup
of
light
rxn
products
PhotorespiraKon
• Some
warm‐climate
plants
•
Have
evolved
a
means
of
dealing
with
photorespiraKon
• C4 photosynthesis
• Most
plants
C3
C4
Photosynthesis
• PEP
carboxylase
•
enzyme
that
binds
with
carbon
dioxide
but
not
with
oxygen
• Forms
a
4‐carbon
compound
(Hence
C4)
• OxaloaceKc
acid
• From
combinaKon
of
CO2 with
a
3‐carbon
molecule
phosphoenolpyruvate
(PEP)
•
Occurs
in
the
mesophyll
cells
•
OxaloaceKc
acid
• then
shucled
to
bundle
sheath
cells
to
Calvin
cycle
• where
CO2 is
released
to
bind
with
rubisco
C4
Photosynthesis
The C4 pathway
C4 leaf anatomy
Mesophyll
cell
Mesophyll cell
CO2
PEP carboxylase
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
Oxaloacetate (4C) PEP (3C)
ADP
Vein
(vascular tissue)
Malate (4C)
Stoma
Bundlesheath
cell
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Vascular
tissue
CAM
Plants
• Crassulacean
Acid
Metabolism
•
Dry‐weather
plants
such
as
cacK
(Crassulacea)
employ
another
form
of
photosynthesis
• CAM
photosynthesis
CAM
Photosynthesis
• CAM
photosynthesis
•
stomata
open
only
at
night
•
Carbon
dioxide
is
“banked”
unKl
sunrise
• ledng
in
and
fixing
carbon
dioxide
• when
photons
supply
energy
for
Calvin
cycle.
Photosynthesis
Photosynthesis Song
You
should
now
be
able
to:
1.
Describe
the
structure
of
a
chloroplast
2.
Describe
the
relaKonship
between
an
acKon
spectrum
and
an
absorpKon
spectrum
3.
Trace
the
movement
of
electrons
in
linear
electron
flow
4.
Trace
the
movement
of
electrons
in
cyclic
electron
flow
5.
Describe
the
similariKes
and
differences
between
oxidaKve
phosphorylaKon
in
mitochondria
and
photophosphorylaKon
in
chloroplasts
6.
Describe
the
role
of
ATP
and
NADPH
in
the
Calvin
cycle
7.
Describe
the
major
consequences
of
photorespiraKon
8.
Describe
two
important
photosyntheKc
adaptaKons
that
minimize
photorespiraKon
5.
Describe
the
similariKes
and
differences
between
oxidaKve
phosphorylaKon
in
mitochondria
and
photophosphorylaKon
in
chloroplasts
6.
Describe
the
role
of
ATP
and
NADPH
in
the
Calvin
cycle
7.
Describe
the
major
consequences
of
photorespiraKon
8.
Describe
two
important
photosyntheKc
adaptaKons
that
minimize
photorespiraKon