Transcript Calvin cycle

Photosynthesis
Autotrophs
Chloroplast histology
Light Reactions
Dark Reaction
C-4 & CAM plants
Reading
Ch 10: Photosynthesis
Homework
Ch 12 Prequiz
Ch 13 prequiz
Ch 14 Prequiz
Test 1 Postponed to 3/13
Q&A Wed 3/8
The Process That Feeds the Biosphere
• Photosynthesis is the process that converts
solar energy into chemical energy
• Directly or indirectly, photosynthesis nourishes
almost the entire living world
Photosynthesis
6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2
6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O
Reactants:
Products:
6 CO2
C6H12O6
12 H2O
6 H2O
6 O2
Remove H = oxidized
Add H = reduced
Light is the driving factor
• electromagnetic energy, aka electromagnetic radiation
• behaves as though it consists of discrete particles,
called photons
• travels in rhythmic waves
– Wavelength is the distance between crests of waves
– determines the type of electromagnetic energy
A pigment abosrbs light in the blue and
green spectrum. What will it look like?
a) Blue
b) Green
c) Blue / Green
d) Red / yellow
Phycourobilin is orange. What colors does
it absorb?
a) Blue / Green
b) ultraviolet
c) Red
d) Red / yellow
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
103 m
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Photosynthetic Pigments: The
Light Receptors
• Pigments - substances that absorb visible light
• Different pigments absorb different wavelengths
• Wavelengths that are not absorbed are
reflected or transmitted
ex: Leaves appear green because chlorophyll reflects
and transmits green light
Fig. 10-7
Light
Reflected
light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Fig. 10-9
RESULTS
Chlorophyll a
Chlorophyll b
Carotenoids
(a) Absorption spectra
400
500
600
700
Wavelength of light (nm)
(b) Action spectrum
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700
Fig. 10-10
CH3
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:
light-absorbing
“head” of molecule;
note magnesium
atom at center
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts
Charge separation - Depart
to a nearby electron acceptor
Energy of electron
e–
Excited
state
Heat
Photon
pigments
(a) Excitation of molecule
Photon
(fluorescence)
Ground
state
(b) Fluorescence
Fig. 10-11
The Two Stages of Photosynthesis
• light reactions (the photo part)
• Calvin cycle (the synthesis part)
H2 O
Light reactions (thylakoids):
– Split H2O
– Release O2
– Reduce NADP+ to NADPH
– Generate ATP from ADP by
photophosphorylation
Light
NADP+
ADP
P
Light
Reactions
Chloroplast
i
thylakoid membrane: 2 photosystems
PS II & PS I
Each Photosystem:
• Chlorophyll a essential
• Accessory pigments
(technically nonessential)
Broaden and protect
 Although PS II
reaction-center chlorophyll a best
at absorbing 680nm (called P680)
Photosystem can absorb more
PS I (P700)
What wavelength of light does the
reaction center chloraphyll a (p680)
of photosystem II absorb?
a) 400 nm
b) 680 nm
c) 700 nm
d) All of the above
Which of the following wavelengths is
absorbed in photosystem II?
a) 400 nm
b) 680 nm
c) 700 nm
d) All of the above
The electron supply & Generation of O2
Photosystems are part of an electron transport chain
•Initial electrons are excited through light photons
•Requires 2 photons for enough energy to reduce
(charge) 1NADP+  NADPH + H+
•Electrons are taken from H2O  O2 + H+ + 2e-
In cellular respiration what does electron
transport do?
What does redox (gaining and then losing
electrons) of cytochrome do?
a) Produces NADH
b) Produces NADP+
c) Pumps H+
d) Creates O2
In cellular respiration, what is the H+
gradient used for?
a) Oxidative phosphorylation
b) Chemiosmosis
= Movement of H+ down conc gradient
c) Turning the crank of ATP synthase
d) Creating ATP
e) All of the above
How is ATP generated in the light
reactions?
a) Substrate phosphorylation
b) Glycolysis
c) Oxidative phosphorylation
ATP generated through oxidative
phosphorylation in the light reactions
Photosystems are part of an electron transport chain
•As in electron transport – multiple redox reactions that are
coupled to H+-pumping
 chemiosmosis  ATP synthase  generation of ATP
What does redox of cytochrome do?
a) Raises free energy of cytochrome
b) Pumps H+
c) Makes NADH
d) Makes FADH2
e) Makes O2
What is the H+ gradient used for?
a) Raises free energy of cytochrome
b) Makes NADH
c) Makes FADH2
d) Makes ATP
e) Makes O2
Cyclic Electron Flow
•only Photosystem I is used
•After photosystem I electrons return to the cytochrome
complex rather than be used to reduce NADP+
•Ultimately, excited electrons return to Photosystem I
Cyclic Electron Flow
Therefore:
•No electrons removed
•No electrons needed and no H2O needed and no O2
produced
•No NADPH is produced, only ATP
Electrons in the Photosystems are
removed and eventually deposited on:
a) ADP
b) NAD+
c) NADP+
d) NADPH
In linear electron flow, where does the
excited electron go after leaving PS I?
a) PS I
b)PS II
c) NADP+
d)ATP synthase
How are the removed electrons in
Photosystem II replaced?
a) From PS I
b) From PS II
c) From H2O
d) From O2
In cyclic electron flow, where does the
excited electron go after PS I?
a) PS II
b)PS I
c) NADP+
d)ATP synthase
The Calvin cycle = CO2 fixation
• Reduces C
• Regenerates starting materials
• uses ATP & NADPH Energy to build sugar
(reduce C)
How is H2O replaced?
a) Produced in CO2 fixation
b) ATP pumps it in
c) Osmosis through vascular bundle
d) Produced in the light reactions
What happens to O2?
a) Used up in calvin cycle
b) Removed through diffusion out
stomata
c) Becomes part of Glucose produced
d) Builds up an can interferes
Products also need to be removed or
equilibrium becomes a problem
The Calvin cycle uses ATP and
NADPH to convert CO2 to sugar
• regenerates its starting material after molecules
enter and leave the cycle
• The cycle builds sugar from smaller molecules
by using ATP and the reducing power of
electrons carried by NADPH
During the Calvin cycle, which of the
following is regenerated for the light
reaction?
a) CO2
b) O2
c) NADP+
d) ATP
Also ADP, but less necessary
Which of the following is the starting
material for the calvin cycle?
+
a) NADP
b)O2
c) Rubisco
d)RuBP
Which of the following is NOT left
at the END calvin cycle?
a)NADP+
b)CO2
c) Rubisco
d)RuBP
What is NADPH used for?
a)Reducing C
b)Oxidizing C
c) Making glucose
d)Carbon fixation
Alternative mechanisms of carbon
fixation have evolved in hot, arid climates
• Dehydration is a problem
• On hot, dry days, plants
close stomata, which:
– conserves H2O
But:
– reduces access to CO2
– & causes O2 to build up
• These conditions favor a
seemingly wasteful process
called photorespiration
Close to preserve H2O
Photorespiration
• In most plants (C3 plants), initial fixation of CO2,
via rubisco, forms a three-carbon compound
• In photorespiration, rubisco adds O2 instead of
CO2 in the Calvin cycle
• Photorespiration consumes O2 and organic fuel
and releases CO2 without producing ATP or
sugar
x2
Photorespiration
• Photorespiration may be an evolutionary relic because
rubisco first evolved at a time when the atmosphere
had far less O2 and more CO2
• Photorespiration limits damaging products (NADPH &
H+) of light reactions that build up in the absence of the
Calvin cycle
• In many plants, photorespiration is a problem because
on a hot, dry day it can drain as much as 50% of the
carbon fixed by the Calvin cycle
C4 Plants
• C4 plants minimize the cost of photorespiration by
incorporating CO2 into four-carbon compounds in
mesophyll cells
• This step requires the enzyme PEP carboxylase
• PEP carboxylase has a higher affinity for CO2 than
rubisco does; it can fix CO2 even when CO2
concentrations are low
• These four-carbon compounds are exported to bundlesheath cells, where they release CO2 that is then used
in the Calvin cycle
Fig. 10-19a
C4 leaf anatomy
Mesophyll cell
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
Vein
(vascular tissue)
Stoma
The C4 pathway
Grana cells
with PEP
Mesophyll
cell
Oxaloacetate (4C)
PEP (3C)
ADP
Malate (4C)
Bundlesheath
cell
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Fig. 10-19b
No Stacked
Membranes
But has Enzymes of
calvin cycle
CO2
PEP carboxylase
Vascular
tissue
CAM Plants
• Some plants, including succulents, use
crassulacean acid metabolism (CAM) to fix
carbon
• CAM plants open their stomata at night,
incorporating CO2 into organic acids
• Stomata close during the day, and CO2 is
released from organic acids and used in the
Calvin cycle
Fig. 10-20
Sugarcane
C4
Pineapple
CAM
CO2
Mesophyll
Organic acid
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
Night
organic acids
(carbon fixation)
Bundlesheath
cell
CO2
Calvin
Cycle
CO2
2 Organic acids
release CO2 to
Calvin cycle
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
In C4 plants where do the light
reactions occur?
a) In the stroma
b) In the mesophyll chloroplasts
c) In the vascular bundle
d) In the thylakoid space
e) epidermis
What is the purpose of the C4
plants?
a)Produce CO2
As C4 compound
b)Concentrate CO2
c) Reduce O2 production
d)Increase H2O usage
Which of the following is NOT a
reactant of Rubisco?
a)CO2
b)O2
c) RuBP
d)PGA
Why is PEP carboxylase preferable
over rubisco?
a) It is present only in mesophyll
b) It is present in the vascular
bundle
c) It has a higher affinity for CO2
d) It has a higher affinity for O2
Draw a comparative enzyme kinetics
graph of PEP carboxylase vs rubisco
depending on substrate conc:?
What happens when you add O2?
NATURE | NEWS
Hacked photosynthesis could boost crop yields
Algal enzyme can speed up rate at which plants make food.
17 September 2014