photosynthesis 2 revised!
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8/9/2019 Photosynthesis 2 REVISED!
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PhotosystemsPhotosystems
Clusters of chlorophyll and other pigments inClusters of chlorophyll and other pigments inthethe thylakoidthylakoid membrane (organized by a set of membrane (organized by a set of proteins in the plant cell)proteins in the plant cell)
Contain few hundred pigment moleculesContain few hundred pigment molecules Chlorophyll aChlorophyll a
Chlorophyll bChlorophyll b
Carotene/Carotene/carotenoidscarotenoids
LightLight--collecting unit of the cellcollecting unit of the cell
Solar panelSolar panel
PhotosystemPhotosystem II andII and PhotosystemPhotosystem II
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Light DependentLight Dependent
ReactionsReactions Produce oxygen gas and convert ADP and NADP+ into theProduce oxygen gas and convert ADP and NADP+ into the
energy carriers ATP and NADPHenergy carriers ATP and NADPH
Take place in the THYLAKOID membrane of chloroplastTake place in the THYLAKOID membrane of chloroplast
Begins with photosystem IIBegins with photosystem II (this was discovered after photosystem I but actually occurs before it)(this was discovered after photosystem I but actually occurs before it)
Photosystem II traps light E and transfers excited ePhotosystem II traps light E and transfers excited e-- to an ETCto an ETC
³water ³water--splitting´ photosystemsplitting´ photosystem Light absorbed by photosystem II is used to breakLight absorbed by photosystem II is used to break--up water moleculesup water molecules
into highinto high--E electrons, oxygen, and H+ ionsE electrons, oxygen, and H+ ions
2 electrons2 electronsreplace lost ereplace lost e-- in chlorophyllin chlorophyll
2 H+ ions2 H+ ions released into the inside of the thylakoid membranereleased into the inside of the thylakoid membrane 1 oxygen atom1 oxygen atom oxygen released into atmosphereoxygen released into atmosphere
Electrons in chlorophyll are excitedElectrons in chlorophyll are excitedpassed along ETCpassed along ETCdodoelectrons in chlorophyll run out?electrons in chlorophyll run out? No: the highNo: the high--E electrons lost by the chlorophyll are replaced by theE electrons lost by the chlorophyll are replaced by the
electrons from ³water splitting´electrons from ³water splitting´
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HighHigh--E electrons move through the ETC fromE electrons move through the ETC from
photosystemphotosystem II toII to photosystemphotosystem II
Energy from electrons is used by molecules inEnergy from electrons is used by molecules inthe ETC to transport H+ ions from thethe ETC to transport H+ ions from the stromastroma
into the inner into the inner thylakoidthylakoid spacespace
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Pigments inPigments in photosystemphotosystem I use Energy fromI use Energy from
light to relight to re--energize the electronsenergize the electrons
NADP+ then picks up these highNADP+ then picks up these high--E electronsE electronsand H+ ions at the outer surface of theand H+ ions at the outer surface of the
thylakoidthylakoid membranemembrane
NADP+ becomes NADPHNADP+ becomes NADPH
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As electrons are passed from chlorophyll to As electrons are passed from chlorophyll to
NADP+, H+ ions are pumped acrossNADP+, H+ ions are pumped across
membranemembrane Inside of Inside of thylakoidthylakoid membrane fills up withmembrane fills up with
positive H+ ions, outside in negativepositive H+ ions, outside in negative
Chemosmosis
Chemosmosis occursoccurs
ATP ATP synthasesynthase turns making ADPturns making ADP ATP ATP
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ETC proteinsETC proteins PhotosystemPhotosystem II (II (recievesrecieves light & splits water)light & splits water)
OxygenOxygen--evolving complexevolving complex
PlastoquinonePlastoquinone
CytochromeCytochrome
PlastocyaninPlastocyanin
PhotosystemPhotosystem I (receives more light)I (receives more light)
FerredoxinFerredoxin
FerrdoxinFerrdoxin--NADPNADP reductasereductase NADPNADPNADPHNADPH
ATP ATP synthasesynthase
ADP ADP ATP ATP
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Over view of LightOver view of Light
Dependent RxnDependent Rxn Use:Use:
ADP ADP
NADP+NADP+
Water Water
Produce:Produce: OxygenOxygen
ATP ATP
NADPHNADPH
Why are these products important?Why are these products important? Provide energy to build energyProvide energy to build energy--containing sugarscontaining sugars
from lowfrom low--energy compounds in Calvin cycleenergy compounds in Calvin cycle
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Calvin Cycle/ LightCalvin Cycle/ Light--
Independent ReactionsIndependent Reactions So what do we have from pour lightSo what do we have from pour light--dependentdependent
rxns?rxns? HighHigh--E electrons stored in ATP and NADPHE electrons stored in ATP and NADPH
³chemical energy´³chemical energy´ But plants cannot store this chemical energy for But plants cannot store this chemical energy for
more than a few minutes«must change thismore than a few minutes«must change thischemical energy into something that can be storedchemical energy into something that can be storedfor long periods of timefor long periods of time
Calvin cycleCalvin cycle Uses ATP and NADPH from lightUses ATP and NADPH from light--dependent rxn todependent rxn to
produce highproduce high--E sugarsE sugars
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Step 1Step 1
Six carbon dioxide molecules enter cycleSix carbon dioxide molecules enter cycle
from atmospherefrom atmosphere
Enzyme adds each CO2 molecule to aEnzyme adds each CO2 molecule to aRibuloseRibulose biphosphatebiphosphate,, RuBPRuBP molecule (a 5molecule (a 5--
carbon molecule) making six unstable 6carbon molecule) making six unstable 6--
carbon moleculescarbon molecules
The six unstable 6The six unstable 6--carbon moleculescarbon molecules
immediately break off into 12 3immediately break off into 12 3--carboncarbon
molecules called 3molecules called 3--phosphoglycerate, 3phosphoglycerate, 3--
PGAPGA
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Step 3Step 3
Two of the G3Ps (twelve 3Two of the G3Ps (twelve 3--carboncarbon
molecules) are removed from the cyclemolecules) are removed from the cycle
Plant uses these two G3Ps (3Plant uses these two G3Ps (3--carboncarbon
molecules) to make sugars, lipids, aminomolecules) to make sugars, lipids, amino
acids, and other compounds plant needsacids, and other compounds plant needs
for metabolism and growthfor metabolism and growth
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Step 4Step 4
Remaining ten G3Ps (3Remaining ten G3Ps (3--carboncarbonmolecules) use ATP and rearrangemolecules) use ATP and rearrange
themselvesthemselves ADP and NADP+ go back to light rxns ADP and NADP+ go back to light rxns
Converted back into RuBP molecules (sixConverted back into RuBP molecules (six55--carbon molecules)carbon molecules)
Calvin cycle begins again with six newCalvin cycle begins again with six newCO2 moleculesCO2 molecules
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Calvin cycle over viewCalvin cycle over view
Uses:Uses:
Six molecules of CO2Six molecules of CO2
NADPHNADPH
ATP ATP
Produces:Produces:
One 6One 6--carbon sugar ³glucose´carbon sugar ³glucose´
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Photosynthesis over viewPhotosynthesis over view
Two sets of reactions work together Two sets of reactions work together
Light dependentLight dependent
Trap energy of sunlight into chemical formTrap energy of sunlight into chemical form
Calvin cycle/light independentCalvin cycle/light independent
Use chemical energy to produce stableUse chemical energy to produce stable--highhigh
energy sugars from carbon dioxide and water energy sugars from carbon dioxide and water
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Factors that effect rate of Factors that effect rate of
photosyntehsisphotosyntehsis Water availabilityWater availability
Shortage of water can slow or stopShortage of water can slow or stop photosynphotosyn..
Adaptations Adaptations Desert plants and conifersDesert plants and conifers
Waxy coatingWaxy coating
TemperatureTemperature PhotosynPhotosyn. Depends on enzymes that function between 0*C . Depends on enzymes that function between 0*C
and 35*Cand 35*C
Low temp. may causeLow temp. may cause photosynphotosyn. to stop. to stop
Intensity of lightIntensity of light Increase light intensity=increase rate of photosynthesisIncrease light intensity=increase rate of photosynthesis
After a certain level of intensity, plant reaches its max rate of After a certain level of intensity, plant reaches its max rate of photosynthesisphotosynthesis
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ProblemsProblems C
alvin cycleC
alvin cycle-- RuBPRuBP binds withC
O2 to make 6binds withC
O2 to make 6--C
C
compound that changes immediately into 3compound that changes immediately into 3-- CarbonCarbon
compounds that eventually make G3P then sugar compounds that eventually make G3P then sugar
Enzyme that catalyzes this reaction is calledEnzyme that catalyzes this reaction is called RubiscoRubisco
Problem withProblem with RubiscoRubisco is that its not good at grabbingis that its not good at grabbing
CO2CO2
When levels of CO2 inside cell are low,When levels of CO2 inside cell are low, RubiscoRubisco startsstarts
grabbing oxygengrabbing oxygen
This causeThis cause photorespiration photorespiration
When plant uses light and consumes oxygen, producingWhen plant uses light and consumes oxygen, producingcarbon dioxidecarbon dioxide
This uses up energy«NOT goodThis uses up energy«NOT good
Big problem on hot, dry days when stomata close and can¶t getBig problem on hot, dry days when stomata close and can¶t get
CO2CO2
So how do plants deal?So how do plants deal?
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Special PlantsSpecial Plants
C4 plantsC4 plants "four "four--carbon´carbon´
plants initially attachCOplants initially attachCO 22 to PEP (to PEP (phosphoenolpyruvatephosphoenolpyruvate) to form the) to form the
four four--carbon compoundcarbon compound oxaloacetateoxaloacetate using the enzyme PEPusing the enzyme PEP
carboxylasecarboxylase.. This takes place inThis takes place in mesophyllmesophyll cells.cells.
OxaloacetateOxaloacetate is then pumped to another set of cells, the bundleis then pumped to another set of cells, the bundle
sheath cells,sheath cells,
In the bundle sheath cells it releases theCOIn the bundle sheath cells it releases theCO 22 for use byfor use by RubiscoRubisco..
Now plant can useCalvin CycleNow plant can useCalvin Cycle
By concentratingCOBy concentratingCO 22 in the bundle sheath cells,C4 plants promotein the bundle sheath cells,C4 plants promote
the efficient operation of theCalvin cycle and minimizethe efficient operation of theCalvin cycle and minimize
photorespiration.photorespiration.
C4 plants include corn, sugar cane, and many other tropical grassesC4 plants include corn, sugar cane, and many other tropical grasses
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Special PlantsSpecial Plants
C AM (C AM (crassulaceancrassulacean acid metabolism) plantsacid metabolism) plants plants initially attachCOplants initially attachCO 22 to PEP (to PEP (phosphoenolpyruvatephosphoenolpyruvate) to form the) to form the
four four--carbon compoundcarbon compound oxaloacetateoxaloacetate using the enzyme PEPusing the enzyme PEP
carboxylasecarboxylase.. They do not fix CO2 during the day and send it to other cells likeC4 They do not fix CO2 during the day and send it to other cells likeC4
plantsplants
C AM plants fix carbon at night and store theC AM plants fix carbon at night and store the oxaloaceteteoxaloacetete in largein large
vacuoles within the cell.vacuoles within the cell.
Then they can open their Then they can open their stomatasstomatas at night (cool weather) and letsat night (cool weather) and lets
CO2CO2 The avoid water loss and to use theCOThe avoid water loss and to use theCO 22 for the Calvin cycle duringfor the Calvin cycle during
the day when it can be driven by the sun's energy.the day when it can be driven by the sun's energy.
C AM plants are more common thanC4 plantsC AM plants are more common thanC4 plants
Ex. Are cacti, pineapples and other succulent plants.Ex. Are cacti, pineapples and other succulent plants.