Download Photosynthesis Sep 16

The overall equation for the
cellular respiration of glucose is
A) C5H12O6 + 6 O2 → 5 CO2 + 6 H2O + energy.
B) 5 CO2 + 6 H2O → C5H12O6 + 6 O2 + energy.
C) C6H12O12 + 3 O2 → 6 CO2 + 6 H2O + energy.
D) C6H12O6 + 6 O2 → 6 CO2 + 6H22O + energy.
E) None of the choices are correct.
Photosynthesis
Review
• Describe the environment inside different
areas in the mitochondria.
• What is the purpose of the electron
transport chain?
• What is the purpose of the Krebs cycle?
Photosynthesis is the process
on which nearly all life depends
Photosynthesis is the opposite
of respiration
Photosynthesis completes the
carbon cycle
Photosynthesis counteracts the
greenhouse effect
Aerobic respiration of glucose is the most
basic means for cells to acquire energy
C6H12O6(s) + 6O2(g)  6CO2(g)+ 6H2O(l) + energy
This is a combustion reaction
Combustion is a kind of redox reaction
Energy in presence of oxygen: ~38 ATP
Photosynthesis can be thought of as the
opposite of respiration
6CO2(g)+ 6H2O(l) + energy  C6H12O6(s) + 6O2(g)
carb. Diox.+H2O+ sunlight glucose+oxygen…
This is still a redox reaction
What is oxidized? What is reduced?
Figure 7.4A
Photosynthesis is the manufacture
of food using energy from the sun
• The site of
photosynthesis is the
chloroplast, which
occurs in plant cells
• Chloroplasts have
their own DNA, and a
double bilayer system
as do mitochondria
Photosynthesis has a few
similarities with respiration
• Metabolic cycles
• Redox molecules (NADP+ instead of
NAD+ and FAD)
• ATP generation
• Specialized organelles (chloroplasts
instead of mitochondria)
Chloroplast structure
• Double bilayer
• Grana made of
Thylakoid membranes
• Stroma is the liquid in
which the grana sit
• Photosynthesis
occurs in chloroplasts
in two stages- light
reactions and dark
LE 10-3
Leaf cross section
Vein
Mesophyll
Stomata
CO2 O2
Mesophyll cell
Chloroplast
5 µm
Outer
membrane
Thylakoid
Thylakoid
Stroma Granum
space
Intermembrane
space
Inner
membrane
1 µm
Where does the oxygen come from, H2O or
CO2?
6CO2(g)+ 6H2O(l) + hν  C6H12O6(s) + 6O2(g)
There are 2 major stages of
photosynthesis
• Light-dependent reactions (“Light
reactions”)
• Light-independent reactions (“Dark
reactions”)
Light and Dark reactions
• Light-dependent reactions
– Water is split
– ATP is formed
– O2 is evolved
• Light-independent reactions
– Carbon is fixed
– Electrons and ATP are consumed
– Glucose precursor (G3P) is formed
LE 10-5_1
H2O
Light
LIGHT
REACTIONS
Chloroplast
LE 10-5_2
H2O
Light
LIGHT
REACTIONS
ATP
NADPH
Chloroplast
O2
LE 10-5_3
H2O
CO2
Light
NADP+
ADP
+ Pi
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Light-dependent reactions
depend on light (duh)
• Some details about
light:
• Visible light is a small
subset of the electromagnetic spectrum
• 400-700nm
• Short wavelengths~
higher energy
Light can excite electrons in atoms
Chlorophyll is a light-absorbing
pigment
• There are other light
absorbing pigments
• Chlorophyll a and b
exist
• Its absorption
spectrum can be
measured in vitro
• We measure light
absorbance with a
spectrophotometer
LE 10-9a
Absorption of light by
chloroplast pigments
Chlorophyll a
Chlorophyll b
Carotenoids
400
500
600
Wavelength of light (nm)
700
Absorption spectra- will these be the same in vivo?
LE 10-8a
White
light
Refracting
prism
Chlorophyll
solution
Photoelectric
tube
Galvanometer
0
Slit moves to
pass light
of selected
wavelength
Green
light
100
The high transmittance
(low absorption)
reading indicates that
chlorophyll absorbs
very little green light.
LE 10-8b
White
light
Refracting
prism
Chlorophyll
solution
Photoelectric
tube
0
Slit moves to
pass light
of selected
wavelength
Blue
light
100
The low transmittance
(high absorption)
reading indicates that
chlorophyll absorbs
most blue light.
Chlorophyll is a fluorescent
molecule
• It absorbs blue
• It re-emits red
• (It can also absorb
red…)
Other pigments absorb different
wavelengths
Different pigments can cooperate to
transfer energy
Leaves are nature’s solar
panels
The light reactions
Consisting of two photosystems,
an electron transport chain, and
ATP synthase
Photosystems
• There are two photosystems:
1) Photosystem II
2) Photosystem I
A photosystem is…
-A special chlorophyll molecule (p680/p700)
-Other pigments
-In a protein bundle, in the thylakoid
membrane
• There are two types of photosystems in the
thylakoid membrane
• Photosystem II functions first (the numbers
reflect order of discovery) and is best at
absorbing a wavelength of 680 nm
• Photosystem I is best at absorbing a
wavelength of 700 nm
• The two photosystems work together to use
light energy to generate ATP and NADPH
LE 10-12
Thylakoid
Photosystem
Photon
Light-harvesting
complexes
Thylakoid membrane
Accessory pigments can
be assembled with
proteins into a
membrane-bound
photosystem
Reaction
center
STROMA
Primary electron
acceptor
e–
At the center there is a
reaction center
Accessory pigments are
a “photon transfer
chain” (Resonance
Energy Transfer)
Transfer
of energy
Special
chlorophyll a
molecules
Pigment
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
LE 10-13_1
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Energy of electrons
e–
Light
P680
Photosystem II
(PS II)
LE 10-13_2
H2O
CO2
Light
NADP+
ADP
CALVIN
LIGHT
CYCLE
REACTIONS
ATP
NADPH
Photosystem II
splits water
O2
Primary
acceptor
Energy of electrons
Water is
oxidized
2H2O  4H+
+O2
[CH2O] (sugar)
2
H+
1/ 2
+
O2
Light
H2O
e–
e–
e–
P680
Photosystem II
(PS II)
LE 10-13_3
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
Energy of electrons
Photosystem II
takes
electrons
from water
and hands
them to the
e- transport
chain
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Pq
2 H+
+
1/ 2 O 2
Light
H2O
e–
Cytochrome
complex
Pc
e–
e–
P680
ATP
Photosystem II
(PS II)
The electron transport chain
makes a proton gradient..
ATP synthase uses the proton
gradient to make ATP
Photosystem 1 hands e-’s to
NADP+ to make NADPH…
LE 10-13_4
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Primary
acceptor
e–
Energy of electrons
Pq
2
H+
1/ 2
+
O2
Light
H2O
e–
Cytochrome
complex
Pc
e–
e–
P700
P680
Light
ATP
Photosystem II
(PS II)
Photosystem I
(PS I)
LE 10-13_5
H2 O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Primary
acceptor
e–
Pq
Energy of electrons
2
H+
e–
H2O
Cytochrome
complex
+
1/2 O2
Light
Fd
e–
e–
NADP+
reductase
Pc
e–
e–
NADPH
+ H+
P700
P680
Light
ATP
Photosystem II
(PS II)
NADP+
+ 2 H+
Photosystem I
(PS I)
…and the NADPH is used to
turn CO2 into Glucose
LE 10-14
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
Photosystem I
A Comparison of Chemiosmosis
in Chloroplasts and Mitochondria
• Chloroplasts and mitochondria generate
ATP by chemiosmosis, but use different
sources of energy
• Mitochondria transfer chemical energy from
food to ATP; chloroplasts transform light
energy into the chemical energy of ATP
• The spatial organization of chemiosmosis
differs in chloroplasts and mitochondria
LE 10-16
Mitochondrion
Chloroplast
CHLOROPLAST
STRUCTURE
MITOCHONDRION
STRUCTURE
H+
Intermembrane
space
Membrane
Lower [H+]
Thylakoid
space
Electron
transport
chain
ATP
synthase
Key
Higher [H+]
Diffusion
Stroma
Matrix
ADP + P i
ATP
H+
LE 10-17
H2 O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
STROMA
(Low H+ concentration)
O2
[CH2O] (sugar)
Cytochrome
complex
Photosystem II
Light
2
Photosystem I
Light
NADP+
reductase
H+
NADP+ + 2H+
Fd
NADPH + H+
Pq
H2O
THYLAKOID SPACE
(High H+ concentration)
1/2
Pc
O2
+2 H+
2 H+
To
Calvin
cycle
Thylakoid
membrane
STROMA
(Low H+ concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
The Calvin Cycle
or, The Citric Acid cycle backward:
ATP and electron carriers are used
to reduce CO2 to glucose
• The Calvin cycle requires three
ingredients:
– Carbon dioxide (catalyzed by rubisco)
– ATP
– Electrons
RubisCO grabs CO2 from the
air
• AKA Ribulose
Bisphosphate
Carboxylase Oxidase
• The carbon fixing
enzyme
• The most common
enzyme on the planet
• Adds 3CO2’s to 3
RuBP’s at a time
LE 10-18_1
H2 O
CO2
Input
Light
(Entering one
CO2 at a time)
3
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
Short-lived
intermediate
P
P
6
3-Phosphoglycerate
3 P
P
Ribulose bisphosphate
(RuBP)
6
6 ADP
CALVIN
CYCLE
Step 1: Carbon Fixation
ATP
LE 10-18_2
H2O
CO2
Input
Light
(Entering one
CO2 at a time)
3
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
6
P
3-Phosphoglycerate
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
CALVIN
CYCLE
Each lap generates 1
G3P
Radioactive CO2
allows tracking of
these molecules
(with liquid N2)
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 Pi
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
LE 10-18_3
H2O
CO2
Input
Light
(Entering one
CO2 at a time)
3
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
6
P
3-Phosphoglycerate
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
CALVIN
CYCLE
6 P
ATP
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
The Importance of
Photosynthesis: A Review
• The energy entering chloroplasts as sunlight
gets stored as chemical energy in organic
compounds
• Sugar made in the chloroplasts supplies
chemical energy and carbon skeletons to
synthesize the organic molecules of cells
• In addition to food production,
photosynthesis produces the oxygen in our
atmosphere
LE 10-21
Light reactions
Calvin cycle
H2O
CO2
Light
NADP+
ADP
+ Pi
RuBP
Photosystem II
Electron transport
chain
Photosystem I
ATP
NADPH
3-Phosphoglycerate
G3P
Starch
(storage)
Amino acids
Fatty acids
Chloroplast
O2
Sucrose (export)
• Which of the following is not an example of
a photoautotroph?
• A) cyanobacteria in freshwater and marine
ecosystems
• B) kelp in an underwater forest
• C) herbs like thyme and basil
• D) fungi
• E) algae
• The energy that excites P680 and P700 is
supplied by
A) electrons passing down the electron
transport chain.
B) the breaking of glucose bonds.
C) ATP.
D) photons.
E) NADPH.