Chapter 6: Photosynthesis Flashcards
Overall equation of photosynthesis (in cyanobacteria and plants)
6CO2 + 6H2O + light —> Glucose + 6O2
What organelle is photosynthesis conducted on?
in the chloroplast
Which layer of the leaf are chloroplasts predominantely located on?
the mesophyll layer
how are chloroplasts created?
through fission of older chloroplasts or by protochloroplasts
which part of the chloroplasts contain porins?
the outer membrane
where is chlorophyll and ATP-synthesizing enzymes found in the chloroplasts?
the inner membrane and thylakoid membranes
T/F: the inner membrane of the chlroroplasts are permeable.
false. It is highly impermeable
a grana is a stack of ____
thylakoids
The oxygen that is released comes from 1) water or 2) CO2
water
photosynthesis ____ water to oxygen, while cell respiration _____ oxygen to water
photosynthesis OXIDIZES water to oxygen, REQUIRING ENERGY
while cell respiration REDUCES oxygen to water, RELEASING ENERGY
where are ribosomes located in the mito? in the chloroplast
in mito: ribosomes in matrix
in chloro: ribosomes in stroma
the process of using light energy to drive electron transport to make ATP is called
photophosphorylation
two stages of photosynthesis
light reactions and dark reactions
pigment in the chloroplasts
chlorophyll
differences between chlorophyll A and B
A; has a methyl group attached to porphoryin ring
B; has a CHO group attached to porphoryin ring instead of chlorophyll
Functions of cartenoid pigment in photosynthesis
act as SECONDARY COLLECTORS to draw excess energy away from excited chlorophyll molecules. presence of other pigments allows greater absorption of photons at other wavelengths.
What can an action spectrum tell you?
its a plot of the rate of photosynthesis produced by light of various wave lengths. identifies which wavelengths are the most effective in bringing about physiological change by photosynthesis
purpose of reaction-center chlorophyll
transfers electrons to the electron acceptor
purpose of antenna molecules:
pigments that do not directly participate in the conversion of light energy. They absorb the light and bounces the energy around TO THE REACTION CENTER
PS___ boosts electrons from below energy level of water to a midpoint, and PS__ boost electrons to level above NADP+, so it can create NADPH
PSIIboosts electrons from below energy level of water to a midpoint, and PSI boost electrons to level about NADP+, so it can create NADPH
why can’t you just immediately transfer the electrons of water to NADPH?
you cannot transfer e- to a higher energy molecule from a lower energy molecule. PSI must energize the electrons to a level ABOVE NADP+ so that it can be transfered down to NADP+
Reaction center of PSII
P680
Reaction center of PSI
P700
primary electron acceptor of the light reactions in total
NADPH
Z scheme
flow of electrons from H2O to NADP+
2 main functions of light energy absorption py pSII
1) removing electrons from water
2) to generate a proton gradient.
what are the associated proteins that are involved with water oxidation of PSII?
D1 and D2 protons. Bind to P680 reaction center and act as COFACTORS involved in electron transport through the photosystem.
What complex are most antenna pigments located in? (for PSII)
the light-harvesting complex II (LHCII)
after light energy is passed to LHCII, the energy is passed to ____
the PSII reaction center P680.
form of excited P680
P680*
P680* transfers an electron to _____, the PRIMARY ACCEPTOR IN PSII, forming ____+ and ____-
P680* transfers an electron to PHEOPHYTIN, the PRIMARY ACCEPTOR IN PSII, forming P680+ and PHEO-
How many electrons are transfered from P680* to pheophytin at a time?
one
P680+ and Pheo- attract each other after the PSII reaction center gives an electron to pheophytin, how is this attraction mitigated?
P680+ and Pheo- move to opposite sides of the membrane. Pheo moves near the stromal side of the membrane and P680 moves to the luminal side of the membrane
Pheo- passes its electrons to ____.
Plastoquinone A (PQA)
plastoquinone is _____ soluble (aqueous or lipid),
lipid soluble.
PQA transferes its electrons to ____, producing ____-
PQB, forming PQB-.
what protein is associated with PQB?
D1 protein
with each electron transfer after PSII, the electron moves closer to the ___ side of the thylakoid membrane
stromal side
How does P680+ (made after donating water’s first electron to Pheophytin) turn back into P680?
P680+ is reduced back to P680 by accepting a second electron.
when the second electron from water is energized by more light, and P680 donates the e- to pheophytin, PQa, to PQB- (- because of first electron), what does PQB- beeome?
PQB2-
PQB2- combines with 2 prrotons to form _____
plastoquinol PQH2
where does the cell get protons to form PQH2?
protons are derived from the stroma, which causes an H+ decrease in the stroma, contributing to the stroma-lumen proton gradient.
When will plastoquinone B dissociate from D1?
when fully reduced to plastoquinOL. (PQB –>PQB- —>PQB2- + 2 protons —> PQH2)
2 e- + PQ + 2H+ —> PQH2
how many protons and photons are needed for the complete oxidation of water?
4 protons, 4 photons.
how many plastoquinol molecules are made by complete oxidation of water.
- each plastoquinoneB can accept two electrons (PQB2-)
4 e- + 2PQ + 4H+ + 4 photons —-> 2 PQH2
process of pulling electrons from water using light energy
photolysis
formation of O2 requires _____ electrons from ____ waters.
4 electrons from two waters.
Photolysis: ___H2O + light —-> ___H+ + ____O2 + ____e-
2H2O + light —-> 4H+ + O2 + 4e-
What side of the thylakoid membrane does water splitting take place?
the lumen side
problem: 2 waters are needed to make oxygen, but PSII can only split one water at a time because it can only hold 2 electrons, how is this solved?
5 metal atoms that are closely associated with the D1 protein form the oxygen evolving complex, which holds the 4 oxidizing equivalents and trasnfers the electrons one at a time to P680+.
the 5 metal atom cluster that is associated with the D1 protein (the ______) passes electrons through a ______ carrier to pass the electrons to PS680+.
he 5 metal atom cluster that is associated with the D1 protein (the OXYGEN EVOLVING COMPLEX) passes electrons through a TYROSINE INTERMEDIATE E- CARRIER to pass the electrons to PS680+.
the accumulation of 4-oxidizing equivalents by the Mn-Ca metal cluster is driven by the successive absorption of _____ by the PSII photosystem
absorption of 4 protons from the stroma. These protons are used to turn 2PQB into 2plastoquinol (PQH2) and are retained in the thylakoid space
the four electrons in the photolysis reaction produces is used to regenerate the _____, while O2 is released as a waste product.
the 4 electrons are used to regenerate the reduced Mn-Ca cluster (metal atoms with D1 oxygen evolving complex)
Photoinhibition
when too high light intensity damages D1 and photolysis cannot occur normally, resulting in toxic oxygen species being formed.
what electron carrier transports the electrons from PSII to PSI?
the 2 molecules of PQH2 fromed by photolysis of H2O.
PQH2 transfers its electrons to _____, while the protons are released into the ____
each PQH2 molecule donates 2e- to CYTB6F, while the 2 protons of each PQH2 molecule are released into the lumen.
Q cycle
the process where each PQH2 molecule translocates 2 protons into the lumen for every 2 electrons it donates to CytB6f, regenerating PQB
electrons from cytb6f are passed to _____
plastocyanin, contains copper.
plastocyanin carries the elctrons to the ____ side of PSI, where they are transfered to the reaction center ____, forming _____
plastocyanin carries the elctrons to the LUMINAL side of PSI, where they are transfered to the reaction center P700, forming P700+
each successive electron transfers are passed to acceptors with ____(lower or higher) electron affinities each time.
higher electron affinities each time. more positive redox reaction.
antenna pigments of photosystem I are located in ___, which passes light energy to P700, turning it into P700*
light harvesting complex I (LHCI), which passes light energy to P700, turning it into P700*
primary electron acceptor of PSI
A0, a chlorophyll A molecule.
P700* transfers an electron to ____, forming ____+ and ____-
to A0, forming P700+ and A0-
How does P700+ go back to P700
accepts another incoming electron from plastocyanin.
P700+ and A0- are attracted to each other. How are these entities mitigated?
separated using cofactors such as phyloquinone and Fe-S clusters.
oxidation of P700* to P700+ occurs on the _____ side of the thylakoid membrane
luminal side
Ao- transfers the elctrons to ___ on the ___side of the membrane
Ao- transfers the elctrons to FE-S centers on the stromal side of the membrane.
electrons are transferred from Fe-S centers in PSI to ____ at the stromal surface of the membane
to ferredoxin.
how many electrons can ferrodoxin hold? how many ferredoxin molecules are needed to create NADPH?
1 electron, you need 2 ferredoxin molecules
______ catalyzes the reduction of NADP+ to form NADPH from ferredoxin
ferredoxin-NADP+ reductase
NADP+ reduction by ferredoxin equation
2Fer(red) + H+ + NADP+ —–> 2Fer (ox) + NADPH
the H+ needed to create NADPH is taken from the ____
taken from the stroma, contributing to the proton gradient
overall PSI reaction
4e- + 2H+ (stroma) + 2NADP+ –(4 photons) —> 2 NADPH
removal of 4e- from water requires _____ photons. But, reduction of NADP+ requires 2 e- to be transfered. therefore, how many photons must be absorbed to generate one O2 and 2 NADPH?
removal of 4e- from water requires 4 photons. 8 photons must be absorbed by the cell to generate one O2 (need 4 e-) and 2 NADPH (2x2= 4 e-).
3 factors that form the H+ gradient
1) splitting of H2O in the lumen
2) oxidation of plastoquinol (PQH2) by cytb6f, releasing protons into the lumen
3) reduction of NADP+ and Plastoquinone (into PQH2).
Conversion of one mole to CO2 to one mole of CH2O requires ____ ATP And ____ NADPH
3 ATP and 2 NADPH
2 parts of chloroplast ATP synthase and locations
CF1: catalytic site. Projects out into STROMA
CFo: mediates proton movement. spans the membrane. protons move from lumen to stroma, while ADP gets phosphorylated.
T/F: the proton gradient in the chloroplast forms a membrane potential
false. When H+ ions are transported, other ions are transported simultaneously, thus there is no change in voltage, like there is in the mitochondria.
pmf in mito is expresssed as electrochemical potential, where as pmf in chloroplasts is largely due to _____
change in pH from concentration gradient. This also happens in the mito along with the established electrochemical potential.
Cyclic photophosphorylation
used for additional atp synthesis. carried out only in PSI, independent of PSII. electrons are passed to ferredoxin and gets routed back to the PSI reaction center rather than being transferred to NADP+ like usual.
protons are being shuttled across thylakoid membrane via transfer of electrons from PQH2 to cytB6f.
autoradiography
identifying radiolabelled compounds compared to known standards, and applying X ray films to a chromatogram. usually tagged with 14C.
C3 plants are named that way because they
produced a #-C intermediate 3 phosphoglycerate as the first compound to be identified during CO2 fixation.
in C3 plants, CO2 is condensed with ____ to form a 6 carbon intermediate
CO2 is condensed with ribulose 1 5 biphosphate to form a 6 carbon intermediate, 6-carboxylase.
6-carboxylase intermediate splits in hald,forming ____
3-phosphoglycerate.
3 phosphoglycerate turns into ____ using atp hydrolysis
BPG
BPG in the calvin cycle is turned into _____ va NADPH oxidation
turned into glyceraldehyde 3 phosphate GAP
in the calvin cycle, GAP can go two routes, what are they?
1) GAP can be moved into cytosol and turned into fructose 16 BP, forming sucrose
2) GAP can be made back into Ribulose 1 5 B phosphate ( 5 carbon compound) via ATP hydrolysis.
plant form of glycogen
starch. formed by GAP molecules in the Calvin cycle.
main enzyme of the calvin cycle
rubisco
overall reaction of the light reaction
12H2O + 12NADP+ +18Pi + 18ADP —> 6 O2 + 12 NADPH + 18 ATP
overall reaction of the calvin benson cycle/dark reaction
6CO2 + 12NADPH + 18ATP —-> C6H12O6 + 12 NADP+ + 18 Pi + 18ADP + 6 H2O
Why does the calvin cycle only happen when the light reactions are also happening in C3 plants?
because of Redox control. Recall: not all electrons that are transferred to ferredoxin go the NADP+. Some electrons go to THIOREDOXIN, which reduce disulfide bridges into sulfhydryl groups, activating the calvin cycle enzymes.
if the light reactions are not happening, thioredoxin cannot get reduced because there is no electron flow going to ferredoxin, thus, the enzymes of the calvin cycles cannot be turned on.
T/F dark reactions are independent of light
false. they are redox controlled by thioredoxin, which can only get activated when light reactions transfer electrons to ferredoxin.
photorespiration
uptake of oxygen and the release of CO2, reverse photosynthesis. occus when rubisco uptakes oxygen rather than CO2.
when rubisco uses oxygen to condense to RuBP rather than Co2, it forms _____, which gets converted to glycolate in the stroma of the chloroplast
it forms 2-phosphoglycolate.
glycolate gets transferred to ____ and eventually leads to CO2 release
peroxisome
when does rubisco fix O2 to RuBp rather than CO2?
when it is too hot and dry. huge waste of energy.
what happens to glycolate when it is in the peroxisome?
it can be turned into glycoxylate, which can get converted into glycine and transferred to the mito.
when glycine is made from glycolate in the peroxisome and transferred to the mito, what happens in the mit? What calvin cycle intermediate is later formed?
2 molecules of glycine are converted to serine, and one molecule of Co2 is released. the serine can be reshutttled back into the chloroplast, and be utilized in carbohydrate synthesis by forming PGA.
for every 2 phosphoglycolate molecules produced, ____ molecule of CO2 that was previously fixed is lost back to the atmostphere
1
in C3 plants, glucose production stops when the rate of photorespiration ____-
equals the rate of CO2 fixation.
How does glucose synthesis in C4 plants still occur even if Co2 levels are very low?
plants uptake CO2 and fix it to PEP i the mesophyll cells converting it to oxaloacetate. this type of fixation can occur at lower levels of CO2 compared to the calvin cycle fixation.
in the bundle sheath cells, the oxaloacetate can be split again and CO2 will be concentrated into high enough concentrations for rubisco to refix CO2 into the calvin cycle. When oxa is split into Co2, pyruvate is formed and can move into the mesophyll cell to form PEP.
Where does fixation of CO2 to PEP occur?
in the mesophyll cells of C4 plants
what happens in the bundle sheath cells? What so special about bundle sheath cells that allow C4 plants to thrive in a hot environement compared to C3 plants?
in the bundle sheath cells, oxaloacetate is split back into Co2 and pyruvate.CO2 can exist in high enough concentrations to drive calvin cycle fixation.
Bundle sheath cells are sealed off from atmospheric gasses, therefor, Rubisco enzyme does not produce energy wasting 2-phosophoglycolate when it fixes O2 instead of Co2, like how it happens to C3 plants in hot conditions.
in C4 plants, the calvin cycle happens in ____
bundle sheath cells.
in C4 plants, the fixation of Co2 to PEP occurs in ____
mesophyll cells
difference between C4 and CAM plants
they both can close their stomata in response to drying temperatures, but, the CAM plant can carry out light-dependent reactions and Co2 fixation at different times of day:
they fix Co2 and open their stomata at night
as CO2 is fixed at night, malate is generated and gets sent to the cell vacuole.
In cam plants, malate is formed at night when Co2 is fixed. in the morning, it is placed in the cytoplasm where it _____
gives up its CO2, which gets fixed to RuBP by Rubsico under conditions of low O2 concentrations (that occur when the stomata is closed, avoiding any external gas flow).
in CAM plants, CO2 entering the cell of CAM PLANTS at ____ gete stored as malate until they can be converted into sugar via Calvin cycle in the ____
CO2 entering the cell of CAM PLANTS at NIGHT gets stored as malate until they can be converted into sugar via Calvin cycle in the MORNING
** CO2 only enters the plant at night because thats when the stomata is open for gas exchange; in the day, its too hot.
