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Plant Phys > Photosynthesis: Carbon Reactions - 5 > Flashcards

Photosynthesis: Carbon Reactions - 5 Flashcards

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1
Q

What provides energy for the assimilation of inorganic carbon into organic material

A

sunlight

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2
Q

What is the Calvin-Benson cycle, biochemical pathway, for

A

the reduction of CO2 to carbohydrates

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3
Q

In what organisms is the Calvin-Benson cycle found in

A

many prokaryotes and all photosynthetic eukaryotes

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4
Q

What two things drive the energy-consuming fixation of atmospheric CO2 through the Calvin-Benson cycle

A

NADPH and ATP

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5
Q

Where does the Calvin-Benson cycle occur

A

chloroplast stroma

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6
Q

What are the three phases of the Calvin-Benson cycle

A

carboxylation
reduction
regeneration

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7
Q

What is the input into the carboxylation phase

A

1 CO2, 1 H2O, with 1 molecule of ribulose 1,5- bisphosphate

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8
Q

What is produced in the carboxylation phase

A

2 molecules of 3-phosphoglycerate

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9
Q

What catalyzes the reaction that occurs in the carboxylation phase

A

Rubisco (a chloroplast enzyme)

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10
Q

Briefly summarize what occurs in the carboxylation phase

A

an H+ is removed from the ribulose 1,5-bisphosphate - CO2 added to unstable rubisco bound intermediate - hydration occurs to create 2 molecules of 3-phosphoglycerate

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11
Q

How many successive reactions are involved in the reduction phase of the Calvin-Benson cycle

A

2

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12
Q

What is the “goal”/ function of the reduction phase

A

reduce the carbon of the 3-phosphogylcerate (produced from the carboxylation phase)

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13
Q

What occurs in the first successive reaction of the reduction phase

A

ATP from the light reactions, phosphorylates 3-phosphoglycerate - creating 1,3-biphosphoglycerate, due to a catalyst

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14
Q

What occurs in the second successive reaction of the reduction phase

A

NADPH from the light reactions, reduces 1,3-biphosphoglycerate to produce glyceraldehyde 3-phosphate, due to a catalyst

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15
Q

How many molecules of ____ are produced from 3 carboxylation and reduction phases

A

6 molecules of glyceraldehyde 3-phosphate

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16
Q

What is the “goal”/function of the regeneration phase of the Calvin-Benson cycle

A

regenerates ribulose 1,5-bisphosphate to ensure continuous assimilation of CO2

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17
Q

What happens to each of the 6 molecules of glyceraldehyde -3-phosphate in the regeneration phase

A

5 molecules reshuffle carbons to restore 3 ribulose 1,5-bisphosphate molecules
1 molecule is the net assimilation of 3 CO2 molecules and is available for carbon metabolism of the plant

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18
Q

Summarize the regeneration phase

A

3CO2 + 3 ribulose 1,5-bisphosphate + 3H2O + 6NADPH + 6H+ + 6ATP PRODUCE:
6 triose phosphates + 6NADP+ + 6ADP = 6Pi

THEN: 5 triose phosphates + 3ATP +H2O PRODUCE 3 ribulose 1,5-bisphosphate + 3ADP +2Pi

The other triose phosphate is net synthesis of CO2 (for metabolic processes)

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19
Q

What are the catalysts involved in the regeneration phase

A

triose phosphate isomerase, aldolase, fructose 1,6-bisphosphate, sedoheptulose 1,7-bisphosphatase, ribulose 5-phosphate epimerase or isomerase, phosphoribulokinase

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20
Q

What is the enzyme that transfers molecules in the regeneration phase

A

transketolase

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21
Q

The Calvin-Benson cycle uses ___ molecules of NADPH and ___ molecules of ATP to assimilate _____ molecules of CO2

Therefore, fixation of 3 CO2 molecules into one triose phosphate uses ____ NADPH and ___ ATP

A

2
3
1

6
9

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22
Q

In the dark, photosynthetic enzymes and concentration of intermediates of the Calvin-Benson cycle are ____

A

low

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23
Q

Enzymes in the Calvin-Benson cycle are activated by what

A

light and the concentration of intermediates increase

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24
Q

Define induction period

A

the time lag between the onset of illumination (light) and the full activation of the Calvin-Benson cycle

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25
Why do regulatory mechanisms exist in the Calvin-Benson cycle
to ensure all intermediates are present in adequate concentrations in the light, and so that cycle turns off in the dark
26
How do chloroplasts adjust the rate of Calvin-Benson cycle reactions
through modifications of enzyme levels and catalytic activities
27
What determine enzyme concentrations in cell compartments
gene expression and protein biosynthesis
28
Where is the small and large subunits of Rubisco encoded in and what does this require
small = nuclear genome large = plastid genome requires coordination between areas
29
Where are the nucleus-encoded and plastid-encoded genes of Rubisco translated
nucleus = cytosol then transported to plastid plastid = stroma
30
how does light modulate the expression of nuclear enzymes
via specific photoreceptors (phytochrome and blue-light receptors)
31
Define anterograde and retrograde regulation
anterograde = signaling from nucleus to chloroplasts retrograde = from nucleus to chloroplasts
32
catalytic rates caused by changes in enzyme concentration are ______ than posttranslational modifications
slower
33
What are the two general mechanisms of light-mediated modifications of the kinetic properties of stromal enzymes
1. changes in covalent bonds that result in chemically modified enzyme 2. modification of noncovalent interactions caused by changes in 1. ionic composition 2. binding of enzyme effectors 3. association with regulatory proteins 4. interaction with thylakoid membranes
34
Rubisco that is inactivate, is reactivated when...
conditions become favourable for photosynthesis
35
Rubisco activase removes ______ from Rubisco and then rubisco is activated by binding of a ____ molecule
sugar phosphates CO2
36
What system is Rubisco regulated by
ferredoxin-thioredoxin system
37
what is the mechanism used in the ferredoxin-thioredoxin system
uses ferredoxin reduced by the electron transport chain and two chloroplast proteins to regulate enzymes
38
Explain what happens to ferredoxin
reduced ferredoxin converts protein thioredoxin to reduced state with the ferredoxin-thioredoxin reductase, then reduced thioredoxin cleaves and causes conformational changes to increase catalytic activity
39
deactivation of thioredoxin takes place when
darkness relieves the electron pressure form the electron transport chain
40
What 3 organelles does photorespiration occur in
chloroplasts, leaf peroxisomes, and mitochondria
41
Define photorespiration
cycle that minimizes the loss of fixed CO2 by the oxygenase activity of rubisco
42
What does Rubisco catalyze
carboxylation and the oxygenation of ribulose 1,5-bisphosphate
43
oxygenation produces ____ molecule of ____ and ____
1 3-phosphoglycerate and 2-phosphoglycolate
44
Photorespiration has been shown to be necessary because of what two reasons
salvages part of the assimilated carbon and links to other metabolic pathways
45
What 3 atoms circulate through photorespiration
carbon, nitrogen, and oxygen
46
What occurs in the carbon cycle
chloroplasts transfer 2 glycolate to peroxisomes and recover 1 glycerate. mitochondria releases 1 CO2 molecule
47
What occurs in the nitrogen cycle
chloroplasts transfer 1 glutamate molecule and recover 1 molecule of NH4+
48
What occurs in the oxygen cycle
Rubisco and glycolate oxidase catalyze incorporation of 2 O2 when 2 ribulose 1,5-bisphosphate enter the photorespiration cycle
49
How many molecules of O2 are reduced in the photorespiratory cycle
3
50
What 3 factors control the balance between the Calvin-Benson cycle and the photorespiration
kinetic properties of Rubisco, temperature, and concentrations of atmospheric CO2 and O2
51
Warmer environments shifts the balance from ____ and toward ____
photosynthesis (carboxylation) and toward photorespiration (oxygenation)
52
What triggered adaptations to handle promoted photorespiration
pronounced reduction in CO2 concentrations and rise is O2
53
CO2 must what 4 barriers in order for the diffusion of CO2 into the chloroplasts in photosynthesis
cell wall, plasma membrane, cytoplasm, and chloroplast envelope
54
What 2 mechanisms did land plants evolve for increasing the concentration of CO2 at Rubisco carboxylation sites
1. C4 photosynthetic carbon fixation 2. Crassulacean acid metabolism (CAM)
55
Define C4 photosynthesis
carbon metabolism which the initial fixation of CO2 is catalyzed by phosphoenolpyruvate carboxylase (PEPCase) (NOT Rubisco like is C3 photosynthesis), producing a 4-carbon compound
56
Examples of C4 plants
corn and sugarcane
57
What doesnt compete in C4 photosynthesis
O2
58
What happens to the C4 molecules
formed in mesophyll cells and move to bundle sheath cells, then decarboxylated, release CO2 that is refixed by Rubisco in the Calvin-Benson cycle
59
____ causes the primary carboxylation of C4 plants
PEPCase
60
The transportation of CO2 from the external atmosphere to the bundle sheath cells in C4 photosynthesis occur through what 5 successive stages
1. fixation (HCO3- by PEPCase) 2. Transport (4-carbon acid to the bundle sheath cells) 3. decarboxylation (CO2 from the Calvin-Benson cycle) 4. Transport (of 3-carbon to mesophyll cells) 5. regeneration (of HCO3- acceptor)
61
Define Kranz Anatomy
particular leaf structure associated with the C4 cycle wreathlike arrangement of mesophyll cells around layer of bundle sheath cells
62
C4 cycle may be driven by _____ or ____
diffusion gradients within a single cell OR gradients between mesophyll and bundle sheath cells
63
_____ regulates the activity of the 3 key C4 cycle enzymes
light NADP-malate dehydrogenase, PEPCase, and pyruvate-phosphate dikinase
64
In C3 plants ____ transport process is required to export triose phosphates vs. in C4 plants it requires ____ transport processes
1 more
65
In hot and dry climates, C4 _____ photorespiration
reduces
66
What two features contribute to overcome the deleterious effects of high temperature
1. CO2 enters mesophyll cells and converted into bicarbonate (PEPCase has high affinity for bicarbonate) and enables C4 plants to reduce stomatal aperture and conserve water while fixing CO2 2. high CO2 concentrations in bundle sheath minimizes oxygenase activity
67
C3 and C4 optimal in what temperatures
20-25 25-35
68
C4 species more abundant in what areas and C3 more abundant in what areas
tropics and subtropics temperate regions
69
Explain CAM mechanism
concentrates CO2 around Rubisco in plants that inhabit arid environments and experience seasonal water availability
70
In CAM, when occurs at night and what occurs during the day
night = uptake and initial carbon fixation day = decarboxylation and reduction of internally released CO2
71
What enhances CAM performance
tightly packed mesophyll cells that restrict CO2 loss during the day
72
CAM pathways are induced by what two factors
water loss or salt stress
73
what increases the concentration of CO2 near Rubisco and reduces the rate of oxygenase activity and increasing the efficiency of photosynthesis in CAM
temporal separation of nocturnal initial carboxylation from diurnal decarboxylation
74
CAM is sensitive to what
environmental conditions
75
What helps conserve water and enhances CO2 concentration near Rubisco during CAM
stomatal closure
76
CAM are able to adjust their patterns of CO2 uptake in response to what
longer-term variations of environmental conditions
77
CAM is also used in aquatic habitats of what conditions
high resistance to gas diffusion restricts availability of CO2
78
photosynthetic assimilation of CO2 yields sucrose and starch where
sucrose = cytosol starch = chloroplasts
79
sucrose flows from where to where and starch flows where to where
sucrose = leaf cytosol to heterotrophic sink tissues starch = accumulates as granules in the chloroplasts
80
Transitory starch
when in the dark CO2 assimilation stops and starch in chloroplasts is degraded
81
What are the 2 functions of transitory starch
1. overflow mechanism that stores photosynthate when the synthesis and transport of sucrose are limited during the day 2. energy reserve to provide adequate supply of carbs at night when sugars are not formed by photosynthesis

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