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BIOL-3221 > Chapter 6: Photosynthesis > Flashcards

Chapter 6: Photosynthesis Flashcards

1
Q

Overall equation of photosynthesis (in cyanobacteria and plants)

A

6CO2 + 6H2O + light —> Glucose + 6O2

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2
Q

What organelle is photosynthesis conducted on?

A

in the chloroplast

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3
Q

Which layer of the leaf are chloroplasts predominantely located on?

A

the mesophyll layer

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4
Q

how are chloroplasts created?

A

through fission of older chloroplasts or by protochloroplasts

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5
Q

which part of the chloroplasts contain porins?

A

the outer membrane

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6
Q

where is chlorophyll and ATP-synthesizing enzymes found in the chloroplasts?

A

the inner membrane and thylakoid membranes

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7
Q

T/F: the inner membrane of the chlroroplasts are permeable.

A

false. It is highly impermeable

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8
Q

a grana is a stack of ____

A

thylakoids

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9
Q

The oxygen that is released comes from 1) water or 2) CO2

A

water

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10
Q

photosynthesis ____ water to oxygen, while cell respiration _____ oxygen to water

A

photosynthesis OXIDIZES water to oxygen, REQUIRING ENERGY

while cell respiration REDUCES oxygen to water, RELEASING ENERGY

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11
Q

where are ribosomes located in the mito? in the chloroplast

A

in mito: ribosomes in matrix

in chloro: ribosomes in stroma

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12
Q

the process of using light energy to drive electron transport to make ATP is called

A

photophosphorylation

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13
Q

two stages of photosynthesis

A

light reactions and dark reactions

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14
Q

pigment in the chloroplasts

A

chlorophyll

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15
Q

differences between chlorophyll A and B

A

A; has a methyl group attached to porphoryin ring

B; has a CHO group attached to porphoryin ring instead of chlorophyll

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16
Q

Functions of cartenoid pigment in photosynthesis

A

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.

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17
Q

What can an action spectrum tell you?

A

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

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18
Q

purpose of reaction-center chlorophyll

A

transfers electrons to the electron acceptor

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19
Q

purpose of antenna molecules:

A

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

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20
Q

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

A

PSIIboosts electrons from below energy level of water to a midpoint, and PSI boost electrons to level about NADP+, so it can create NADPH

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21
Q

why can’t you just immediately transfer the electrons of water to NADPH?

A

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+

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22
Q

Reaction center of PSII

A

P680

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23
Q

Reaction center of PSI

A

P700

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24
Q

primary electron acceptor of the light reactions in total

A

NADPH

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25
Q

Z scheme

A

flow of electrons from H2O to NADP+

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26
Q

2 main functions of light energy absorption py pSII

A

1) removing electrons from water

2) to generate a proton gradient.

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27
Q

what are the associated proteins that are involved with water oxidation of PSII?

A

D1 and D2 protons. Bind to P680 reaction center and act as COFACTORS involved in electron transport through the photosystem.

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28
Q

What complex are most antenna pigments located in? (for PSII)

A

the light-harvesting complex II (LHCII)

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29
Q

after light energy is passed to LHCII, the energy is passed to ____

A

the PSII reaction center P680.

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30
Q

form of excited P680

A

P680*

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31
Q

P680* transfers an electron to _____, the PRIMARY ACCEPTOR IN PSII, forming ____+ and ____-

A

P680* transfers an electron to PHEOPHYTIN, the PRIMARY ACCEPTOR IN PSII, forming P680+ and PHEO-

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32
Q

How many electrons are transfered from P680* to pheophytin at a time?

A

one

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33
Q

P680+ and Pheo- attract each other after the PSII reaction center gives an electron to pheophytin, how is this attraction mitigated?

A

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

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34
Q

Pheo- passes its electrons to ____.

A

Plastoquinone A (PQA)

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35
Q

plastoquinone is _____ soluble (aqueous or lipid),

A

lipid soluble.

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36
Q

PQA transferes its electrons to ____, producing ____-

A

PQB, forming PQB-.

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37
Q

what protein is associated with PQB?

A

D1 protein

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38
Q

with each electron transfer after PSII, the electron moves closer to the ___ side of the thylakoid membrane

A

stromal side

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39
Q

How does P680+ (made after donating water’s first electron to Pheophytin) turn back into P680?

A

P680+ is reduced back to P680 by accepting a second electron.

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40
Q

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?

A

PQB2-

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41
Q

PQB2- combines with 2 prrotons to form _____

A

plastoquinol PQH2

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42
Q

where does the cell get protons to form PQH2?

A

protons are derived from the stroma, which causes an H+ decrease in the stroma, contributing to the stroma-lumen proton gradient.

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43
Q

When will plastoquinone B dissociate from D1?

A

when fully reduced to plastoquinOL. (PQB –>PQB- —>PQB2- + 2 protons —> PQH2)

2 e- + PQ + 2H+ —> PQH2

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44
Q

how many protons and photons are needed for the complete oxidation of water?

A

4 protons, 4 photons.

45
Q

how many plastoquinol molecules are made by complete oxidation of water.

A
  1. each plastoquinoneB can accept two electrons (PQB2-)

4 e- + 2PQ + 4H+ + 4 photons —-> 2 PQH2

46
Q

process of pulling electrons from water using light energy

A

photolysis

47
Q

formation of O2 requires _____ electrons from ____ waters.

A

4 electrons from two waters.

48
Q

Photolysis: ___H2O + light —-> ___H+ + ____O2 + ____e-

A

2H2O + light —-> 4H+ + O2 + 4e-

49
Q

What side of the thylakoid membrane does water splitting take place?

A

the lumen side

50
Q

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?

A

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+.

51
Q

the 5 metal atom cluster that is associated with the D1 protein (the ______) passes electrons through a ______ carrier to pass the electrons to PS680+.

A

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+.

52
Q

the accumulation of 4-oxidizing equivalents by the Mn-Ca metal cluster is driven by the successive absorption of _____ by the PSII photosystem

A

absorption of 4 protons from the stroma. These protons are used to turn 2PQB into 2plastoquinol (PQH2) and are retained in the thylakoid space

53
Q

the four electrons in the photolysis reaction produces is used to regenerate the _____, while O2 is released as a waste product.

A

the 4 electrons are used to regenerate the reduced Mn-Ca cluster (metal atoms with D1 oxygen evolving complex)

54
Q

Photoinhibition

A

when too high light intensity damages D1 and photolysis cannot occur normally, resulting in toxic oxygen species being formed.

55
Q

what electron carrier transports the electrons from PSII to PSI?

A

the 2 molecules of PQH2 fromed by photolysis of H2O.

56
Q

PQH2 transfers its electrons to _____, while the protons are released into the ____

A

each PQH2 molecule donates 2e- to CYTB6F, while the 2 protons of each PQH2 molecule are released into the lumen.

57
Q

Q cycle

A

the process where each PQH2 molecule translocates 2 protons into the lumen for every 2 electrons it donates to CytB6f, regenerating PQB

58
Q

electrons from cytb6f are passed to _____

A

plastocyanin, contains copper.

59
Q

plastocyanin carries the elctrons to the ____ side of PSI, where they are transfered to the reaction center ____, forming _____

A

plastocyanin carries the elctrons to the LUMINAL side of PSI, where they are transfered to the reaction center P700, forming P700+

60
Q

each successive electron transfers are passed to acceptors with ____(lower or higher) electron affinities each time.

A

higher electron affinities each time. more positive redox reaction.

61
Q

antenna pigments of photosystem I are located in ___, which passes light energy to P700, turning it into P700*

A

light harvesting complex I (LHCI), which passes light energy to P700, turning it into P700*

62
Q

primary electron acceptor of PSI

A

A0, a chlorophyll A molecule.

63
Q

P700* transfers an electron to ____, forming ____+ and ____-

A

to A0, forming P700+ and A0-

64
Q

How does P700+ go back to P700

A

accepts another incoming electron from plastocyanin.

65
Q

P700+ and A0- are attracted to each other. How are these entities mitigated?

A

separated using cofactors such as phyloquinone and Fe-S clusters.

66
Q

oxidation of P700* to P700+ occurs on the _____ side of the thylakoid membrane

A

luminal side

67
Q

Ao- transfers the elctrons to ___ on the ___side of the membrane

A

Ao- transfers the elctrons to FE-S centers on the stromal side of the membrane.

68
Q

electrons are transferred from Fe-S centers in PSI to ____ at the stromal surface of the membane

A

to ferredoxin.

69
Q

how many electrons can ferrodoxin hold? how many ferredoxin molecules are needed to create NADPH?

A

1 electron, you need 2 ferredoxin molecules

70
Q

______ catalyzes the reduction of NADP+ to form NADPH from ferredoxin

A

ferredoxin-NADP+ reductase

71
Q

NADP+ reduction by ferredoxin equation

A

2Fer(red) + H+ + NADP+ —–> 2Fer (ox) + NADPH

72
Q

the H+ needed to create NADPH is taken from the ____

A

taken from the stroma, contributing to the proton gradient

73
Q

overall PSI reaction

A

4e- + 2H+ (stroma) + 2NADP+ –(4 photons) —> 2 NADPH

74
Q

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?

A

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-).

75
Q

3 factors that form the H+ gradient

A

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).

76
Q

Conversion of one mole to CO2 to one mole of CH2O requires ____ ATP And ____ NADPH

A

3 ATP and 2 NADPH

77
Q

2 parts of chloroplast ATP synthase and locations

A

CF1: catalytic site. Projects out into STROMA
CFo: mediates proton movement. spans the membrane. protons move from lumen to stroma, while ADP gets phosphorylated.

78
Q

T/F: the proton gradient in the chloroplast forms a membrane potential

A

false. When H+ ions are transported, other ions are transported simultaneously, thus there is no change in voltage, like there is in the mitochondria.

79
Q

pmf in mito is expresssed as electrochemical potential, where as pmf in chloroplasts is largely due to _____

A

change in pH from concentration gradient. This also happens in the mito along with the established electrochemical potential.

80
Q

Cyclic photophosphorylation

A

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.

81
Q

autoradiography

A

identifying radiolabelled compounds compared to known standards, and applying X ray films to a chromatogram. usually tagged with 14C.

82
Q

C3 plants are named that way because they

A

produced a #-C intermediate 3 phosphoglycerate as the first compound to be identified during CO2 fixation.

83
Q

in C3 plants, CO2 is condensed with ____ to form a 6 carbon intermediate

A

CO2 is condensed with ribulose 1 5 biphosphate to form a 6 carbon intermediate, 6-carboxylase.

84
Q

6-carboxylase intermediate splits in hald,forming ____

A

3-phosphoglycerate.

85
Q

3 phosphoglycerate turns into ____ using atp hydrolysis

A

BPG

86
Q

BPG in the calvin cycle is turned into _____ va NADPH oxidation

A

turned into glyceraldehyde 3 phosphate GAP

87
Q

in the calvin cycle, GAP can go two routes, what are they?

A

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.

88
Q

plant form of glycogen

A

starch. formed by GAP molecules in the Calvin cycle.

89
Q

main enzyme of the calvin cycle

A

rubisco

90
Q

overall reaction of the light reaction

A

12H2O + 12NADP+ +18Pi + 18ADP —> 6 O2 + 12 NADPH + 18 ATP

91
Q

overall reaction of the calvin benson cycle/dark reaction

A

6CO2 + 12NADPH + 18ATP —-> C6H12O6 + 12 NADP+ + 18 Pi + 18ADP + 6 H2O

92
Q

Why does the calvin cycle only happen when the light reactions are also happening in C3 plants?

A

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.

93
Q

T/F dark reactions are independent of light

A

false. they are redox controlled by thioredoxin, which can only get activated when light reactions transfer electrons to ferredoxin.

94
Q

photorespiration

A

uptake of oxygen and the release of CO2, reverse photosynthesis. occus when rubisco uptakes oxygen rather than CO2.

95
Q

when rubisco uses oxygen to condense to RuBP rather than Co2, it forms _____, which gets converted to glycolate in the stroma of the chloroplast

A

it forms 2-phosphoglycolate.

96
Q

glycolate gets transferred to ____ and eventually leads to CO2 release

A

peroxisome

97
Q

when does rubisco fix O2 to RuBp rather than CO2?

A

when it is too hot and dry. huge waste of energy.

98
Q

what happens to glycolate when it is in the peroxisome?

A

it can be turned into glycoxylate, which can get converted into glycine and transferred to the mito.

99
Q

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?

A

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.

100
Q

for every 2 phosphoglycolate molecules produced, ____ molecule of CO2 that was previously fixed is lost back to the atmostphere

A

1

101
Q

in C3 plants, glucose production stops when the rate of photorespiration ____-

A

equals the rate of CO2 fixation.

102
Q

How does glucose synthesis in C4 plants still occur even if Co2 levels are very low?

A

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.

103
Q

Where does fixation of CO2 to PEP occur?

A

in the mesophyll cells of C4 plants

104
Q

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?

A

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.

105
Q

in C4 plants, the calvin cycle happens in ____

A

bundle sheath cells.

106
Q

in C4 plants, the fixation of Co2 to PEP occurs in ____

A

mesophyll cells

107
Q

difference between C4 and CAM plants

A

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.

108
Q

In cam plants, malate is formed at night when Co2 is fixed. in the morning, it is placed in the cytoplasm where it _____

A

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).

109
Q

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 ____

A

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.

BIOL-3221 (6 decks)

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