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BIOL 2321 - Cell Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What organisms have chloroplasts?

A

all plants

unicellular plant-like protists

multicellular plant-like protists (like kelp)

some photosynthetic prokaryotes (cyanobacteria)

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2
Q

In what 2 ways do chloroplasts arise?

A

by fission from other mature chloroplasts

from their non-photosynthetic precursors, proplastids

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3
Q

in higher plants, where are chloroplasts located?

A

in the mesophyll layer of leaves

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4
Q

Approximately how many chloroplasts are there per cell in leaves of higher plants?

A

20-40

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5
Q

How many membranes do chloroplasts have?

A

2

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6
Q

What separates the double membrane envelope of chloroplasts?

A

an intermembrane space

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7
Q

Describe the outer envelope membrane of chloroplasts

A

not very selective, it allows many molecules to pass through its large porins

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8
Q

Describe the inner envelope membrane of chloroplasts

A

highly impermeable and substances require a specific transporter to enter

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9
Q

Aside from the double membrane, what are the two components of chloroplasts?

A

thylakoids

stroma

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10
Q

Describe thylakoids

A

flattened sacs separated from the envelope with their own distinct membrane

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11
Q

T or F: thylakoids have their own distinct membrane

A

true

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12
Q

How are thylakoids arranged?

A

in stacks called grana (pl.) or granum (s.)

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13
Q

What do thylakoid membranes contain?

A

all the protein components for photosynthesis

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14
Q

What occurs in the thylakoid lumen?

A

it is where H+ is pumped to create a gradient for ATP synthesis

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15
Q

T or F: all thylakoids are stacked as grana

A

false! some are singular and not stacked

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16
Q

What are thylakoids that are singular and not stacked called?

A

stroma thylakoids

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17
Q

What is the purpose of stroma thylakoids?

A

they usually connect stacks of grana thylakoids

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18
Q

Describe the stroma

A

the fluid outside the thylakoid in chloroplasts

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19
Q

What 5 things does the stroma of chloroplasts contain?

A

a single, small, circular DNA chromosome

ribosomes

enzymes

lipids

starch granules

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20
Q

T or F: the stroma of chloroplasts contains DNA

A

true

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21
Q

Describe the structure of the DNA found in the stroma of chloroplasts. What is its purpose?

A

it is a single, circular DNA chromosome

it codes for about 65 synthesizing chloroplast proteins

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22
Q

What are the ribosomes found in stroma of chloroplasts associated with?

A

the surface of thylakoids

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23
Q

What are the enzymes of the stroma of chloroplasts for?

A

the Calvin Cycle

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24
Q

What purpose do the lipids and starch granules in the stroma of chloroplasts have?

A

they are for stored energy

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25
Q

What is an example of a protein the stroma DNA chromosome codes for?

A

RUBisCO

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26
Q

Where are most of the chloroplast proteins synthesized and translated?

A

synthesized in the nucleus

translated in the cytoplasm

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27
Q

What do the proteins synthesized in the nucleus but bound for the chloroplasts require to be directed to the chloroplasts?

A

they require import into the chloroplast with a specific N-terminal stroma targeting signal

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28
Q

What kind of signal do chloroplast-bound proteins synthesized and translated outside of the chloroplast have?

A

an N-terminal stroma signal

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29
Q

What are the 2 large translocation complexes in chloroplasts and where are they located?

A

Toc = outer envelope membrane

Tic = inner envelope membrane

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30
Q

Which of the 2 translocation complexes will proteins encounter first on their journey to the chloroplast stroma?

A

TOC

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31
Q

What happens to proteins when they encounter the TOC complex?

A

they are unfolded by cytosolic chaperone proteins

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32
Q

What chaperone protein associates with the unfolded polypeptide as it is translocated through TOC and TIC into the stroma? What is its purpose?

A

Hsp70

encourages refolding in the stroma

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33
Q

What happens to the protein once its in the stroma?

A

an enzyme cleaves the N-terminal stroma targeting sequence and

a barrel-shaped chaperone (Hsp60) folds the proteins

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34
Q

What do proteins bound for the thylakoid membrane or lumen have in addition to the signal sequence for the stroma?

A

they will have an additional thylakoid transfer domain sequence that targets them for either the thylakoid lumen or membrane

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35
Q

Why are ribosomes usually bound to the thylakoid surface?

A

so they can directly translocate a protein that was synthesized from genes within the chloroplast DNA through the thylakoid membrane

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36
Q

What happens to proteins synthesized from genes within the chloroplast DNA?

A

the chloroplast ribosome will directly translocate the protein through the thylakoid membrane

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37
Q

What is the overall purpose of the light reactions of photosynthesis?

A

they capture energy from light and use it to remove and energize electrons from water

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38
Q

in the light reactions, where do the high-energy electrons move to once removed from water?

A

through redox reactions in the ETC

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39
Q

What happens in the ETC?

A

energy is used to pump protons and create an electrochemical gradient

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40
Q

What is the electrochemical gradient produced by the ETC? What is its purpose?

A

a proton gradient that is used to drive ATP synthase (photophosphorylation)

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41
Q

What is the final electron acceptor at the end of the ETC?

A

the carrier NADP+

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42
Q

What is the BASIC flow of energy through the light reactions?

A

light energy –> electrical energy –> chemical energy

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43
Q

What are the inputs of the light reactions?

A

H2O

light

NADP+ (oxidized electron carrier)

ADP + Pi

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44
Q

What are the outputs of the light reactions?

A

NADPH (reduced e. carrier)

ATP

O2 (waste)

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45
Q

Is NADP+ the reduced or oxidized version?

A

oxidized

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46
Q

Is NADPH the reduced or oxidized version?

A

reduced

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47
Q

What two things are used to drive the Calvin Cycle?

A

ATP + the final electron carrier NADP+ (NADPH when it has accepted the electron)

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48
Q

What is the purpose of the Calvin Cycle?

A

carbon fixation

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49
Q

Describe carbon fixation

A

the conversion of CO2 into simple sugars (CH2O)

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50
Q

What is the purpose of the dark reactions?

A

to fix carbon by converting CO2 into simple sugars (CH2O), chemical energy that can be stored for when there’s no light for the light reactions to occur

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51
Q

What is the BASIC flow of energy through the dark reactions?

A

transient chemical energy –> stored chemical energy

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52
Q

What are the inputs of the dark reactions?

A

CO2

NADPH (reduced version)

ATP

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53
Q

What are the outputs of the dark reactions?

A

C3H6O3 (simple sugar, later converted to glucose)

NADP+ (oxidized)

ADP + Pi

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54
Q

Where in the chloroplast do the light reactions occur?

A

in the thylakoid membranes

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55
Q

Where does the calvin cycle/dark reactions occur in the chloroplast?

A

the stroma

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56
Q

What are some major similarities between the mitochondria and chloroplasts/cellular respiration and photosynthesis?

A

both have energy-harvesting electron transport chains

both pump H+ to make proton gradients

both have compartments in organelles where pH is different

the reactions are almost exactly the reverse

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57
Q

What is the reaction for photosynthesis?

A

light energy + 6 H2O + 6 CO2 –> C6H12O6 + 6 O2

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58
Q

What 3 things does the inner membrane system surrounding thylakoids contain?

A

light-absorbing pigments (organized in protein photosystem complexes)

electron carriers

proteins related to ATP synthesis + ATP synthase

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59
Q

What are photosystems? where are they located?

A

protein complexes that contain light-absorbing pigments

located in the inner membrane system that surrounds the thylakoids

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60
Q

What are the 2 basic parts of photosystems?

A

light harvesting complexes

reaction centre

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61
Q

T or F: only the light harvesting complexes have pigments

A

false! the LHC and the reaction center have pigments

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62
Q

What are pigments?

A

special chemicals that can absorb certain wavelengths of visible light

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63
Q

What light is harnessed to undergo photosynthesis?

A

only light that is absorbed by pigments

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64
Q

What is unique about the molecular structure of pigments?

A

they usually have a metal ion (ex. Mg2+) fixed in the center of a carbon ring with conjugated double bonds

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65
Q

What is the key photosynthetic pigment?

A

chlorophyll a

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66
Q

What are the two antenna pigments?

A

chlorophyll b

carotenoids

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67
Q

Why do plants appear green?

A

because the pigments are absorbing a specific wavelength of light and reflecting green wavelengths

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68
Q

What wavelengths of visible light do pigments absorb? what colours are associated with these?

A

~450 nm

purple-blue

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69
Q

What happens when a pigment molecule absorbs light?

A

when a photon of light is absorbed by a pigment molecule, one or more electrons in the pigment is excited from its ground state to an unstable excited state with higher potential energy

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70
Q

What are the 3 strategies for an excited electron to return to ground state?

A
  1. release of heat and a photon of a different wavelength (fluorescence)
  2. transfer of energy to a neighbouring chlorophyll
  3. transfer of the excited electron to a neighbouring electron acceptor
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71
Q

Which of the 3 strategies for an excited electron to return to ground state are the most common in photosynthesis?

A

transfer of energy to a neighbouring chlorophyll

transfer of the excited electron to a neighbouring electron acceptor

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72
Q

What happens to the chlorophyll if the excited electron is transferred to a neighbouring electron acceptor?m

A

it will need to replenish its lost electron by receiving a new one from an electron donor

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73
Q

Which pigments are in the light harvesting complexes?

A

many, but these include the antenna pigments (chlorophyll b and carotenoids)

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74
Q

Which pigments are in the reaction center?

A

a special chlorophyll a dimer

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75
Q

Describe the transfer of energy in the pigments of the light harvesting complexes

A

pigments transfer energy from the excited electron amongst each other towards the reaction center

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76
Q

How does the reaction center transfer energy from the excited electron?

A

the special chlorophyll a dimer directly converts the light energy into chemical energy

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77
Q

How does energy move from pigment molecule to pigment molecule in the light harvesting complexes? What does this really mean?

A

it always transfers to a neighbouring pigment molecule of equal or lower energy

aka the neighbouring pigment molecule must absorb light of equal or longer wavelength

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78
Q

How is the energy gradient that is required to move energy from the light harvesting complexes into the reaction center maintained?

A

neighbouring pigment molecules are carefully selected and kept at specific distances from one another to promote the energy transfer

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79
Q

What are the two types of photosystems in the light reactions?

A

PSI and PSII

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80
Q

Where do the photosystems access light energy?

A

in their respective light harvesting complexes

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81
Q

Which of the two photosystems occurs in the light reactions first?

A

PSII then PSI

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82
Q

How are PSII and PSI distinguished?

A

by their chlorophyll a dimers

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83
Q

What is the chlorophyll a dimer found in the PSII?

A

P680

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84
Q

What is the chlorophyll a dimer found in the PSI?

A

P700

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85
Q

Why is the chlorophyll a dimer of PSII called P680?

A

the chlorophyll a dimer absorbs light at 680 nm

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86
Q

Why is the chlorophyll a dimer of PSI called P700?

A

the chlorophyll a dimer absorbs light at 700 nm

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87
Q

What is the overall direction electrons move?

A

from H2O –> PSII –> ETC –> PSI –> ETC –> NADP+

88
Q

What happens to NADP+ once it accepts the electrons?

A

it’s reduced to NADPH

89
Q

What do the photosystems use their chlorophyll a molecules for?

A

to separate charge

90
Q

How do the photosystems use their chlorophyll a molecules to separate charge?

A

the pair of chlorophyll a molecules donate their excited electron to an electron carrier =

chlorophyll a is now positively charged

electron carrier is now negatively charged

91
Q

What is the result of the photosystems using their chlorophyll a molecules to separate charge?

A

when the excited electrons are donated from the chlorophyll a molecules to an electron carrier:

chlorophyll a becomes positively charged

electron carrier becomes negatively charged

92
Q

When the electrons are donated from the chlorophyll a pairs in the photosystems to an electron carrier, what happens?

A

the electron moves from a primary acceptor (the electron carrier). to the ETC

93
Q

What is the purpose of the ETC?

A

to help create a proton gradient to synthesize ATP

94
Q

What happens to the chlorophyll a dimer that has given up its excited electrons?

A

it is positively charged and needs to replenish its electrons

it will receives electrons from the splitting of water (photolysis)

95
Q

What is photolysis?

A

the splitting of water

96
Q

How do positively charged chlorophyll a dimers replenish their lost electrons?

A

by receiving electrons from the splitting of water

97
Q

How many ETC chains are there in the light reactions?

A

2

98
Q

What is at the end of the first ETC?

A

photosystem 1

99
Q

What is at the end of the second ETC?

A

the final electron acceptor, NADP+

100
Q

T or F: there’s only one type of electron carrier in the light reactions of photosynthesis

A

false! there’s many (ex. Q, PC, FD)

101
Q

What are some examples of the electron carriers in the light reactions of photosynthesis?

A

NADP+

Q

FD

PC

102
Q

What is the Z pathway?

A

the energy diagram between the 2 photosystems which forms a ‘Z’

103
Q

Describe the BASIC steps of the energy diagram between the 2 photosystems

A

PSII boosts electrons from an energy point lower than water to a midway point

the ETC carries the electrons down in energy to the PSI

PSI boosts electron energy from a midway point to an energy level above the NADP+

104
Q

How does the Z pathway begin?

A

sunlight excites electrons of antenna pigments in the light harvesting complexes

105
Q

What happens after sunlight excites electrons of the antenna pigments of the LHCs?

A

energy moves through the pigments (as pigments absorb light at a successively longer wavelength) to the reaction center with the P680 dimer

106
Q

What happens to the energy when it reaches the P680 dimer in the reaction center?

A

from P680, electrons are passed on to an electron acceptor and leave behind an oxidized photosystem II (P680+)

107
Q

What happens to the PSII after the electrons are passed to an electron acceptor?

A

it is oxidized to P680+

108
Q

Where do the electrons go after they have been passed from the P680 in PSII to the electron acceptor?

A

the electrons are transferred to an ETC and they move down the chain while releasing energy and creating a proton gradient

109
Q

While the electrons are being moved down the ETC, what happens to the oxidized P680+ photosystem?

A

the lost electrons are replaced by electrons from water when it is split

110
Q

How does energy move through PSI (P700)?

A

light hits PSI (P700) which excites its electrons

energy moves through PSI to the reaction center with the P700 chlorophyll a dimer

111
Q

What happens after energy from excited electrons reach the P700 chlorophyll a dimer?

A

the electrons are transferred to the PSI primary e acceptor and leave behind an oxidized P700+

112
Q

What reduces the oxidized P700+?

A

incoming electrons from the ETC1 reduce it back to P700

113
Q

What transfers electrons from the PSI (P700) to and through the ETC?

A

primary electron acceptors

114
Q

What is the last step of the Z pathway?

A

the electrons reduce NADP+, the final electron acceptor, to NADPH

115
Q

Describe the composition of the PSII reaction center

A

it is a complex of 20+ polypeptides, most of which are integral membrane proteins

this complex contains the special chlorophyll a pigment dimer

116
Q

What type of proteins are most of the polypeptides that make up the PSII reaction center?

A

integral membrane proteins

117
Q

Why is the special chlorophyll a dimer of the PSII called P680?

A

because the pigments most effectively absorb light at the 680 nm wavelength

118
Q

What molecule is closely associated with the reaction center of PSII?

A

pheophytin

119
Q

What is pheophytin?

A

a molecule similar to chlorophyll but lacks an Mg2+

it is the primary electron acceptor for PSII

120
Q

What is the function of pheophytin? What is the result of its function?

A

in the PSII reaction center, electrons move from P680 to pheophytin to generate the separation of charge:

P680+ and Pheo-

121
Q

Where are the electrons transferred from pheophytin?

A

to plastoquinone (PQ)

122
Q

Where does the electron transfer between pheophytin and plastoquinone move the electron toward?

A

toward the stromal side of the membrane

123
Q

What becomes the oxidizing agent as a result of the electron transfer between pheophytin and plastoquinone?

A

P680+

124
Q

Describe plastoquinone

A

(PQ)

a lipid-soluble molecule similar to ubiquinone in the mitochondria

125
Q

What is the function of PQ?

A

it accepts 2 electrons from pheophytin and 2 H+ (from stroma) to become plastoquinol (PQH2)

126
Q

What is the reduced form of plastoquinone (PQ)? How does it become this?

A

plastoquinol (PQH2)

when PQ accepts 2 e- and 2 H+

127
Q

How many plastoquinones are there? What are they and where are they located?

A

2

PQA and PQB

located near the stromal side of the PSII reaction center

128
Q

What is the function of PQA?

A

It is the type of plastoquinone that accepts electrons from Pheo- and passes them on to PQB

129
Q

What is the function of PQB?

A

it accepts the electrons passed from PQA

130
Q

What is the result of the electron transfer from Pheo- –> PQA –> PQB?

A

PQBH2

131
Q

What does PQBH2 do?

A

it dissociates from PSII and moves laterally through the membrane

132
Q

T or F: P680+ is a relatively weak oxidizing agent

A

FALSE! it is the strongest oxidizing agent ever found in a biological system

133
Q

Why is it important than P680+ is a strong oxidizing agent?

A

so it can pull electrons from very stable water molecules

134
Q

What is the photolysis equation?

A

2 H2O –4 photons–> 4 H+ (lumen) + O2 + 4 e-

135
Q

In order to produce one oxygen molecule, how many water molecules are required and how many electrons are lost from the water?

A

2 water molecules required

4 electrons lost

136
Q

What is the discrepancy between the amount of electrons produced by photolysis and the amount of electrons P680+ can accept?

A

P680+ only donated 1 electron to Pheo- and therefore can only accept one electron from water to regenerate P680

137
Q

What is the oxygen evolving complex?

A

an enzyme that splits water and is associated with the PSII on its luminal surface

138
Q

What does the oxygen evolving complex contain?

A

an Mn-Ca cluster that can donate 4 of its electrons

139
Q

What is the purpose of the Mn-Ca cluster? When does it do its function?

A

it donates 4 of its electrons, one at a time, to the chlorophyll a dimer every time a photon hits and P680+ is produced

140
Q

When will the oxygen evolving complex split water molecules? How many molecules will it split

A

once the Mn-Ca cluster has lost 4 electrons, the OEC can split 2 water molecules

141
Q

What is produced by the OEC splitting 2 water molecules? what happens to these products?

A

the 4 electrons from water are used to regenerate the Mn-Ca cluster

the 4 protons accumulate in the thylakoid lumen and contribute to the proton gradient for ATP synthesis

O2 is released as a waste product

142
Q

What happens to the 4 electrons produced by the OEC splitting water?

A

they are used to regenerate the Mn-Ca cluster

143
Q

What happens to the 4 protons produced when the OEC splits 2 water molecules?

A

they accumulate in the thylakoid lumen to help produce the proton gradient for ATP synthesis

144
Q

What happens to the O2 produced when the OEC splits 2 water molecules?

A

it’s released as a waste product

145
Q

After water is split, what happens to the reduced plastoquinol (PQH2)?

A

it moves through the membrane bilayer while carrying the electrons to the cytochrome b6-f complex

146
Q

Where does plastoquinol carry electrons to?

A

the cytochrome b6-f complex

147
Q

What cycle is involved in the transfer of 2 electrons from plastoquinol to the cytochrome b6-f complex?

A

the Q cycle

148
Q

What is the Q cycle?

A

the cycle involved in the transfer of 2 electrons from plastoquinol to the cytochrome b6-f complex

149
Q

What happens in the Q cycle?

A

4H+ are pumped into thylakoid lumen from the stroma which creates the proton gradient

150
Q

What is produced from the Q cycle?

A

the proton gradient

151
Q

What does the cytochrome b6-f complex transfer the 2 electrons to?

A

plastocyanin

152
Q

What is plastocyanin?

A

a small peripheral membrane protein on the thylakoid interior side that accepts electrons from the cytochrome b6-f complex

153
Q

What is plastocyanin analogous to in the mitochondria?

A

cytochrome c

154
Q

Where does plastocyanin carry electrons to?

A

the luminal side of PSI where they are transferred to the chlorophyll a dimer P700

155
Q

How does light energy move from the LHC of PSI towards the reaction center at the chlorophyll a dimer (P700)?

A

antenna pigments move light energy in the same way as in PSII LHC

156
Q

where do electrons move from the P700 dimer?

A

to a primary acceptor called Ao

157
Q

What is Ao?

A

a chlorophyll molecule that acts as a primary acceptor of the electrons from P700 of PSI

158
Q

What results from the transfer of the electrons from P700 to the primary acceptor Ao?

A

a separation of charge:

P700 oxidized to P700+

Ao reduced to Ao-

159
Q

Is Ao- a strong oxidizing or reducing agent?

A

strong reducing agent

160
Q

What does Ao- transfer electrons to?

A

to other molecules in PSI and eventually to ferredoxin

161
Q

How is P700+ reduced back to P700?

A

by electrons incoming from plastocyanin from the ETC1

162
Q

What is ferredoxin? Where is it located?

A

a small, water-soluble polypeptide on the stromal side of the thylakoid membrane that accepts electrons

163
Q

What does ferredoxin transfer electrons to?

A

Ferredoxin-NADP+ Reductase (FNR)

164
Q

What does ferredoxin-NADP+ Reductase pass electrons to?

A

NADP+

165
Q

What are the electron carriers involved in the transfer of electrons from H2O to PSII and from PSII to PSI?

A

chlorophyll a P680 to pheophytin

Pheo- to plastoquinone (PQA)

WATER (separate): water to Mn-Ca of OEC to P680+

PQA to PQB

PQBH2 (plastoquinol) to cytochrome b6-f complex

cytochrome b6-f complex to plastocyanin

plastocyanin to P700

166
Q

What are the electron carriers involved in the transfer of electrons from PSI to NADP+?

A

P700 to Ao

Ao- to others and then ferredoxin

plastocyanin (from ETC1) to P700+

ferredoxin to ferredoxin-NADP+ Reductase

FNR to NADP+

167
Q

What are the 3 sources of the H+ gradient?

A

photolysis

Q cycle

Reduction of NADP+

168
Q

How is photolysis a source of H+ gradient?

A

it generates H+ in the thylakoid lumen

169
Q

How is the Q cycle a source of H+ gradient?

A

it transfers the H+ from the stroma to the thylakoid lumen

170
Q

How is the reduction of NADP+ a source of H+ gradient?

A

H+ concentration is reduced on the stromal side of the thylakoid

171
Q

What are the major products of the light reactions?

A

NADPH (reduced NADP+)

ATP

O2 (waste)

172
Q

What is the major process of the dark reactions?

A

the Calvin Cycle

173
Q

Where does the Calvin Cycle occur?

A

the stroma

174
Q

What sugar does the Calvin Cycle produce?

A

glyceraldehyde 3-phosphate (G3P)

175
Q

What does the Calvin Cycle require that is produced in the light reactions per G3P made?

A

9 ATP

6 NADPH

176
Q

Why is the Calvin Cycle referred to as a cycle?

A

the starting material (RuBP) is regenerated

177
Q

What are the 3 stages of the Calvin Cycle?

A
  1. fixing CO2 into an organic molecule
  2. reducing the organic molecule with NADPH and ATP to form a sugar
  3. regenerating the CO2 acceptor
178
Q

How many carbons of G3P does each cycle of the Calvin Cycle fix?

A

ONE

179
Q

How many times does the Calvin Cycle have to occur in order to net produce one G3P molecule? why?

A

3 times

because only one carbon is fixed per cycle and G3P has 3 carbons

180
Q

What molecule incorporates CO2 during carbon fixation?

A

Ribulose bisphosphate (RuBP)

181
Q

How many carbons does RuBP have?

A

5

182
Q

What does RuBP stand for?

A

Ribulose bisphosphate

183
Q

What is required for the incorporation of CO2 into RuBP?

A

the enzyme Rubisco

184
Q

T or F: rubisco is the most prevalent enzyme on earth. Explain why/why not

A

true because it is required for the fixation of carbon from CO2

185
Q

What does the incorporation of CO2 into RuBP produce?

A

an unstable 6C intermediate

186
Q

What does the unstable 6C intermediate of the CO2 + RuBP quickly turn into?

A

it splits into two 3C molecules of 3-phosphoglycerate (PGA)

187
Q

How many carbons are in each of the 2 molecules of 3-PGA?

A

3

188
Q

What does PGA stand for?

A

3-phosphoglycerate

189
Q

1 CO2 + 1 RuBP –Rubisco–> ?

A

2 molecules of 3-phosphoglycerate

190
Q

What happens to the 3-PGA?

A

it is phosphorylated by ATP and converted into 1,3-BPG

191
Q

What does the phosphorylation of 3-PGA produce? How many ATP molecules does this take per turn?

A

1,3-bisphosphoglycerate (BPG)

takes 2 ATP per turn

192
Q

What does BPG stand for?

A

1,3-bisphosphoglycerate

193
Q

What is produced when 1,3-BPG is reduced by the NADPH carrier?

A

glyceraldehyde 3-phosphate (G3P)

194
Q

What does G3P stand for?

A

glyceraldehyde 3-phosphate

195
Q

What reduces BPG to G3P?

A

the electrons stored in the NADPH carrier

196
Q

What is G3P?

A

a 3 carbon sugar produced by the carbon fixation reactions

197
Q

How many CO2 molecules are fixed in 6 turns of the Calvin Cycle?

A

6

198
Q

How many ATP and NADPH are used in 6 turns of the Calvin Cycle?

A

12 ATP + 12 NADPH

2 of each per turn

199
Q

How many GAPs (aka G3Ps) are produced by 6 turns of the Calvin Cycle?

A

12 (2 per turn)

200
Q

Why do the numbers of the Calvin Cycle matter?

A

not all the G3Ps produced are net Calvin Cycle products

201
Q

What happens to most of the G3Ps (GAPs) produced by the Calvin Cycle?

A

they are used up in regenerating the starting product, RuBP

202
Q

Of the 12 GAPs (G3Ps), how many will be NET products of the Calvin Cycle?

A

2 of these 12 will be net products of the Calvin Cycle

203
Q

What are the 2 net G3P products produced by the Calvin Cycle used for?

A

to make sugars

204
Q

What are the 2 possibilities for the 2 net G3Ps produced by the Calvin Cycle?

A

they can be converted into starch granules and be stored in the stroma

OR

they can be exported to the cytosol to make sucrose

205
Q

What happens to the remaining 10 GAPs that were not used to make sucrose or starch?

A

they will regenerate 6 molecules of RuBP again

206
Q

How many molecules of RuBP will the remaining 10 GAPs make? What else is required for this process?

A

6 molecules of RuBP

also requires 6 ATP total or 1 ATP per turn

207
Q

What is the full name of rubisco?

A

ribulose bisphosphate carboxylase/oxidase

208
Q

Why is the carboxylase/oxidase ending of the rubisco name important?

A

it means that rubisco can use CO2 or O2 as a substrate and if rubisco is using O2 as a substrate, the sugars produced will not be the same as if it were CO2

209
Q

What is the desired product of RuBP + CO2?

A

2x 3-PGA

210
Q

What is the undesired product from RuBP + O2? How is it produced?

A

2-phosphoglycolate

produced when rubisco uses O2 as a substrate instead of CO2

211
Q

Why can rubisco use CO2 or O2 as a substrate?

A

it first appeared billions of years ago when CO2 was plentiful in the atmosphere and O2 was not

there was no selective pressure to adapt a binding site that distinguished between CO2 and O2

212
Q

What process occurs when Rubisco uses O2 as a substrate?

A

photorespiration

213
Q

Why is it problematic for rubisco to use O2 as a substrate?

A

it produces an undesirable 2C product which will undergo photorespiration which releases up to half of the unfixed carbon to be released as CO2 in the atmosphere = a huge waste of a plant’s energy

214
Q

Why is the ability of rubisco to use O2 as a substrate particularly problematic in hot climates?

A

because plants close their stomata on hot days (prevent water loss) which blocks the influx of CO2 –> O2 produced by photosynthesis can build up in the leaf

215
Q

What is C3 carbon fixation?

A

the normal Calvin Cycle process which produces G3P from CO2

216
Q

What is C4 carbon fixation?

A

a method of carbon fixation which reduces photorespiration in some plant groups that can fix CO2 into 4-carbon oxaloacetate

BIOL 2321 - Cell Biology (26 decks)

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