key themes energy acquisition in photosynthesis: from sunlight to atp & sugar production lecture...
TRANSCRIPT
Key Themes
Energy acquisition in photosynthesis: from sunlight to ATP & sugar production
Lecture 8: Photosynthesis
Yesterday’s Exit Ticket
Glucose
Process: Gycolysis
Location: Cytosol
# ATPs:
Citric Acid Cycle
Location: Mitochon. MatrixProducts Released: CO2
Location: Mitoch. Inner MembraneProducts Released: H20
# ATPs:
# ATPs:
Oxidative Phosphorylation
2
NADH NADH + FADH2
Pyruvate
2 2 34
Time to Photosynthesize!
Fig. 1.5
Sunlight
Ecosystem
Heat
Heat
Cyclingof
chemicalnutrients
Producers(plants and other photosynthetic
organisms)
Chemical energy
Consumers(such as animals)
PhotosynthesisSun = ultimate energy source
Mint kept mouse alive, but not in the basement…
http://www.americanscientist.org/issues/id.800,y.1998,no.6,content.true,page.1,css.print/issue.aspx
"the injury which is continually done to the atmosphere by the respiration of such a large number of animals ... is, in part at least, repaired by the vegetable creation"
Joseph Priestly, 1771-1772
http://home.nycap.rr.com/useless/priestly/priestly.html
(a) Plants
(c) Unicellular protist
10 µm
1.5 µm
40 µm(d) Cyanobacteria
(e) Purple sulfur bacteria
(b) Multicellular alga
PhotosyntheticOrganisms
Fig. 10.2
What is the goal of photosynthesis?
• Light Chemical Energy• Form C-H bonds for energy storage• Harness the sun’s energy to do so
Sugar [CH2O] + O2
Light + CO2 + H20(energy)
O2 + some ATP sugarsH2O
H+ & e-
CO2Light
dermalinstitute.com; gaia-health.com
O2 + some ATPH2O
H+ & e-
Light
Step 1: Light-Dependent
Reactions
What is the goal of photosynthesis?
O2 + some ATP sugarsH2O
H+ & e-
CO2Light
Step 2: Light-Independent
Reactions(Calvin Cycle)
What is the goal of photosynthesis?
Overview of Photosynthesis
solar energy
Solar energy drives production of energy-rich ATP & NADPH
ATP & NADPH drive conversion of CO2 to energy-rich sugar
Fig. 10.5
O2 is a waste product
O2
Because ATP is too unstable to serve as a storage form of energy, C-H bonds in sugars are instead
used for energy storage.
Fig. 8.8
ATP: Energy carrier
solar energy
Fig. 10.5
Step 1: Light-Dependent Reactions• Occur in: thylakoid membranes of chloroplasts• Start with: H2O, NADP+, ADP, Pi• Produce: NADPH, ATP, and O2
O2
Leaf cross section Vein
Stomata CO2 O2
Mesophyll cell
5 µmThylak
oidspace
Thylakoid
Granum
Stroma
1 µm
Fig. 10.3
Plant photosynthesis occurs in chloroplasts
Chloroplast
Leaf cross section Vein
Stomata CO2 O2
Chloroplast
5 µmThylakoid
space
Thylakoid
GranumStroma
1 µm
Fig. 10.3
Plant photosynthesis occurs in chloroplasts
• Inner membranes (thylakoids): Light reactions (light collection by chlorophyll & electron transport)
• Fluid space (stroma): Conversion of CO2 to sugars in Calvin cycle
Photosystems made up of chlorophylls
absorb sunlight
Photosystems use light energy to
propel energized electrons into the
photosynthetic electron transport
chain
Fig. 10.14
e-
• Most chlorophylls absorb light energy & pass it on to a special chlorophyll that gives up an electron.
Fig. 10.12
H2O H+ +
O2
water-splitting enzyme
e-
• This special chlorophyll gets an electron back from a water molecule, leaving behind H+ (protons*) and O2.
*H = 1 proton + 1 electron
e-
• The energized electron is propelled through the electron transport chain.
Fig. 10.12
H2OH+ + O2
e-
Fig. 10.14
Light
ADP +
i H+
ATPP
ATPsynthase
ToCalvinCycle
STROMA(low H+ concentration)
Thylakoidmembrane
THYLAKOID SPACE(high H+ concentration)
STROMA(low H+ concentration) Photosystem
IIPhotosystem I4 H+
4 H+
Light
NADP+ + H+
NADPH
+2 H+
H2O O2
e–
e– 1/21
2
3
NADP+reductase
Now, let’s look at this whole process within the context of the thylakoid membranes
Fig. 10.17
Here’s an animation of photosynthetic electron transport.
http://www.colorado.edu/ebio/genbio/10_17LightReactions_A.html
“When sunlight is absorbed into a plant, it triggers a chain reaction of electrons, which move from one molecule to the next…
The Berkeley researchers borrowed this [chain reaction] for their artificial forest, but instead of relying on the pigment in chloroplast to trigger electron movement they used semiconductors.”
What is the goal of photosynthesis?
O2 + some ATP sugarsH2O
H+ & e-(NADPH)
CO2
Light
dermalinstitute.com; gaia-health.com
Original electron donor in photosynthesis
Electron acceptors from ETC: NADP+
Electron donors for Calvin cycle Electron acceptor
from Calvin cycle
Protons are pumped into the inner thylakoid space and ATP is formed in the stroma
Light
ADP +
i H+
ATPP
ATPsynthase
ToCalvinCycle
STROMA(low H+ concentration)
Thylakoidmembrane
THYLAKOID SPACE(high H+ concentration)
STROMA(low H+ concentration) Photosystem
IIPhotosystem I4 H+
4 H+
Light
NADP+ + H+
NADPH
+2 H+
H2O O2
e–
e– 1/21
2
3
NADP+reductase
Fig. 10.17
+
Pi
H+
ADP
ATP
Fig. 9.14
Light
ADP i H
+
ATPP
ATPsynthaseSTROMA
(low H+ concentration)
Thylakoidmembrane
THYLAKOID SPACE(high H+ concentration)
STROMA(low H+ concentration)Photosystem
IIPhotosystem I4
H+
4 H+
Light
+2 H+
H2O O
2
e–
e– 1/
2
NADP+reduct
ase
P i
Inner thylakoid space
stroma
The ATP synthase “turbine”
Fig. 10.16
Same principle used for ATP formation in chloroplasts & mitochondria
Fig.8.7
O2 + some ATP sugarsH2O
H+ & e-
CO2
Light
Step 1: Light-Dependent
Reactions
NADP+
NADPH
What is the goal of photosynthesis?
O2 + some ATP sugarsH2O
CO2
Light
Step 2: Light-Independent
Reactions(Calvin Cycle)
H+ & e-
NADP+
NADPH
What is the goal of photosynthesis?
solar energy
Fig. 10.5
Step 2: Calvin Cycle• Occurs in: stroma (liquid space inside chloroplasts)• Starts with: CO2, NADPH, ATP• Produces: Sugar, NADP+, ADP, Pi
O2
LightReactions:
Light collection & electron transport
CO2
NADP+
ADPP i+
RuBP 3-PhosphoglycerateCalvin
Cycle
G3PATP
NADPHStarch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2Fig. 10.21 O2
LightReactions:
Light collection & electron transport
CO2
NADP+
ADPP i+
RuBP 3-Phosphoglycerate
Calvin
Cycle
G3PATP
NADPHStarch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2Fig. 10.21
Rubisco:combines RuBP with
CO2 to form 3-PG
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
In this diagram of the Calvin cycle, compound X is the CO2 acceptor. If
CO2 is cut off, then
A. X and 3PG will both increase.
B. X will increase, 3PG decrease.
C. X will decrease, 3PG increase.
D. X and 3PG will both decrease.
What is the goal of photosynthesis?
• Light Chemical Energy• Form C-H bonds for energy storage• Harness the sun’s energy to do so
Sugar [CH2O] + O2
Light + CO2 + H20(energy)
O2 + some ATP sugarsH2O
H+ & e-
CO2
Light
dermalinstitute.com; gaia-health.com
5 min break
Wtfcontent.com
http://www.youtube.com/watch?v=sQK3Yr4Sc_k&feature=fvwrel
Hank’s Crash Course in Photosynthesis
Plant adaptations to their environments
Flickriver.com
What does a plant need?
Light, CO2, H2O, (nutrients)
Travelsfy.com
LightReactions:
Light collection & electron transport
CO2
NADP+
ADP
P i+
RuBP 3-Phosphoglycerate
Calvin
Cycle
G3PATP
NADPHStarch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
Fig. 10.21
Acclimation to sun vs. shade?
Sun
Calvin Cycle enzymes
Shade
+++
+
When LIGHT varies:
Light, CO2, H2O, (nutrients)
When H2O varies:
Light, CO2, H2O, (nutrients)
Travelsfy.com
Stomate
Stomata
CO2H2O
O2
When H2O varies:
Light, CO2, H2O, (nutrients)Travelsfy.com; minnestota.publicradio.org; mccullagh.org
CO2H2O
O2
In wet environments
• Stomata can stay wide open• CO2 is relatively unlimited in
plant cells
In semi-arid environments
• Stomata are kept ajar to reduce water loss
• CO2 is acquired more slowly
In dry environments
• Stomata are kept closed in the heat of the day
• Stomata are opened at night to acquire CO2
When H2O varies:
Light, CO2, H2O, (nutrients)Travelsfy.com; minnestota.publicradio.org; mccullagh.org
In wet environments• Stomata can stay wide open• CO2 is relatively unlimited in
plant cells
In semi-arid environments
• Stomata are kept ajar to reduce water loss
• CO2 is acquired more slowly
In dry environments• Stomata are kept closed in
the heat of the day• Stomata are opened at night
to acquire CO2
“C3”Most plants
More “C4” plantsMany grasses
More “CAM” plantsCacti, many other desert succulents
Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).
LightReactions:
Light collection & electron transport
CO2
NADP+
ADPPi+
RuBP
3-Phosphoglycerat
eCalv
inCycl
e
G3P
ATP
NADPH
Starch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2Fig. 10.21
Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).
The C4 pathway
CO2PEP carboxylase
Oxaloacetate (4C)
Malate (4C)
PEP (3C) AD
PATP
Pyruvate (3C)CO2
CalvinCycle
Sugar
Vasculartissue
Fig. 10.19
Some plants (C4 plants) use an additional CO2 fixation cycle before the Calvin cycle: The enzyme PEP carboxylase “fixes” CO2 into a sugar with 4 carbonsOnce enough new CO2 has been stored in the 4-C sugar, it moves into the Calvin Cycle Leaf surface
Inside of leaf
C4 plants:• This process allows the Calvin Cycle to run smoothly
despite low CO2 conditions
The C4 pathway
Mesophyllcell
CO2PEP carboxylase
Oxaloacetate (4C)
Malate (4C)
PEP (3C) AD
PATP
Pyruvate (3C)CO2
Bundle-sheathcell
CalvinCycle
Sugar
Vasculartissue
Fig. 10.19
CAM plants:• Take the C4 process one step further
The C4 pathway
Mesophyllcell
CO2PEP carboxylase
Oxaloacetate (4C)
Malate (4C)
PEP (3C) AD
PATP
Pyruvate (3C)CO2
Bundle-sheathcell
CalvinCycle
Sugar
Vasculartissue
• CO2 is collected and converted to 4-carbon sugar at night
• Sugar is stored in vacuoles
• In the morning, stomata close and malic acid is broken down to enter the Calvin Cycle
LightReactions:
Light harvestingand photosynthetic electron transport
CO2
NADP+
ADP
Pi+
RuBP
3-Phosphoglycerate
CalvinCycleG3PATP
NADPH Starch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
Fig. 10.21
Why isn’t every plant a C4 plant?
Advantage of C3 plants
C3 plants need less energy since they don’t run two cycles
Advantage in less sunny, moist, cool, CO2-rich climates. Typically more cold-tolerant.
Mountainphotographer.com
Since ATP is too unstable, C-H bonds in sugars are used for energy storage.
In both mitochondria and chloroplasts:
• Carbon conversion cycles in fluid space:Calvin cycle vs. citric acid cycle (Krebs cycle)(CO2 sugar) (sugar CO2)
• Electron transport chain & ATP synthase on inner membranes (thylakoid or mitochondrial)
LightReactions:
Light collection & electron transport
CO2
NADP+ADPPi+
RuBP
3-Phosphoglycerat
eCalv
inCycl
eG3P
ATP
NADPH
Starch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2Fig. 10.21
Photosynthesis
Carbon source:
Carbon product:
CO2
Sugar (C-H bonds)
Ultimate energy source:
Final energy-rich product:
Sunlight
Sugar (C-H bonds)
H (electron + H+) source: Water (H-O-H)
Electrontransport
andATP synthase
Mitochondrion
ATP
Electrons carried off by
NADH & FADH2
Citricacidcycle
ATP
Glucose Pyruvate
Glycolysis
Electronscarried off by NADH
Fig. 9.6
Some SomeATP
Lots of
Cytosol
Respiration
Carbon source:
Carbon product:
Organic molecules with C-H bonds
CO2
Final energy-rich product: ATP
Energy source:C-H bondsH (electron + H+) source:
C-H bonds
Fig. 10.16
Same principle used for ATP formation in mitochondria & chloroplasts
Fig.8.7
Fig. 10.16
Citric acid cycle Calvin cycle
In both mitochondria and chloroplasts:
• Carbon conversion cycles in fluid space
• Electron transport chain & ATP synthase on inner membranes
Today’s Exit Ticket
Process:
Location:
CO2
+
H2O
O2
Fig. 10.21
Process:
Location: