Photosynthesis (Chapter 12) Flashcards
______ is a herbicide that blocks electron transport in the photosystem I protein complex, leading to plant cell death.
Paraquat
The photosynthetic electron transport system and carbon fixation (Calvin cycle) reactions together convert ______, ______, and ______ into ______, ______, and ______.
sunlight energy, CO2 and H2O
chemical energy (ATP, NADPH), molecular oxygen, and the triose phosphate glyceraldehyde-3-phosphate.
Whys is photosynthesis important for non photosynthetic organisms?
They provide metabolic fuel in the form of carbohydrate
True o False: Glyceraldehyde-3-phosphate feeds into the anabolic gluconeogenesis pathway where it is used as a precursor for glucose synthesis.
True
True or False: The emergence of photosynthetic organisms on Earth led to significant increases in the level of O2 in the atmosphere and directly affected the evolution of multicellular organisms that use aerobic respiration for energy conversion.
True
True or False: The ability to fix CO2 into organic compounds was a later evolutionary trait.
False, it was an earlier evolutionary trait
How many steps are there in the photosynthetic electron transport and photophosphorylation system?
5
What is the first step in the photosynthetic electron transport and photophosphorylation system?
Photon (4) absorption by the PSII leads to activation of the photosynthetic electron transport system and generation of O2
In the first step, ______ e- are generated from the _______ (oxidation/reduction) of ______ water molecules.
4
oxidation, 2
What is the second step in the photosynthetic electron transport and photophosphorylation system?
Electrons flow through the photosynthetic electron transport system, which includes the electron carriers (PQ), (PC), and (Cytb6f).
What is the function of step 2?
Electron flow through cytochrome b6f results in the buildup of a chemiosmotic proton gradient across the thylakoid membrane.
What is the third step in the photosynthetic electron transport and photophosphorylation system?
Photon absorption by PSI continues the series of electron transfer reactions.
True or False: In the third step, the final electron acceptor in this pathway is NADPH, which is oxidized to form NADP+.
False, NADP+ which is reduced to form NADPH.
What is the fourth step in the photosynthetic electron transport and photophosphorylation system?
The process of photophosphorylation occurs, in which ATP synthesis is catalyzed by the chloroplast ATP synthase complex.
Why does the fourth step occur?
In response to proton flow from the thylakoid lumen into the stroma
What is the fifth step in the photosynthetic electron transport and photophosphorylation system?
CO2 fixation by the Calvin cycle leads to the formation of glyceraldehyde-3-phosphate
What is G-3-P used for?
Used to make hexose sugars
True or False: Energy conversion from ATP hydrolysis and NADPH oxidation is used to drive the Calvin cycle reactions.
True
The ______ disks are folded regions of the thylakoid membrane where proteins in the photosynthetic electron transport system are located.
thylakoid
The aqueous compartment outside of the thylakoid membrane, but inside the inner chloroplast membrane is the _______.
Stroma
What part of the chloroplast contains all of the calvin cycle enzymes?
Stroma
The thylakoid membrane can be found in a stack of thylakoid disks called a ______ or in an unstacked region called the ______.
granum, lamella.
True or False: Photosynthetic electron transport leads to proton translocation into the stroma and the production of NADPH in the thylakoid lumen.
False, translocation into the thylakoid lumen and the production of NADPH in the stroma.
Why is the AT synthase complex orientated outward from the lumen?
So that ATP synthesis occurs in the stromal compartment
What does photosynthesis accomplish for the cell?
The photosynthetic electron transport system converts light energy into redox energy, which is used to generate ATP by chemiosmosis and reduce NADP+ to form NADPH
Calvin cycle enzymes use the energy available from ATP and NADPH to reduce CO2 to form glyceraldehyde-3-phosphate, a triose phosphate that can be used to synthesize glucose.
Photosynthetic cells use the triose phosphates produced by the Calvin cycle as a chemical energy source for mitochondrial respiration, which is independent of light.
True or False: Photosynthetic organisms are autotrophs because they derive energy from light rather than from organic materials.
True
What is the overall net reactions of the photosynthetic electron transport system
2 H2O + 8 photons + 2 NADP+ + ~3 ADP + ~3 Pi
—> O2 + 2 NADPH + 2 H+ + ~3ATP
What is the overall net reactions of the Calvin cycle.
3 CO2 + 6 NADPH + 9 ATP + 5 H2O —–> glyceraldehyde-3-phosphate + 6NADP+ + 9 ADP + 8 Pi
What are the four key enzymes of the photosynthetic electron transport system and the Calvin cycle?
photosystem II (P680 reaction center),
cytochrome b6f (proton translocation),
photosystem I (P700 reaction center)
Rubisco
Photon absorption by chlorophyll molecules results in ______, ______, or ______.
resonance energy transfer, fluorescence, photooxidation
What occurs during resonance energy transfer?
The energy released by the excited chlorophyll molecule returning to the ground state (Chl1* → Chl1) is transferred to a nearby chlorophyll molecule, which causes it to be in the excited state (Chl2 → Chl2*)
What occurs during fluorescence?
(Chl1* → Chl1)
True or False: Fluorescence does result in useful work being performed by the plant as a result of light absorption.
False, does not result in useful work
What occurs during photo oxidation?
An electron from the excited chlorophyll molecule is passed directly to a nearby acceptor molecule of higher (more positive) reduction potential, such as pheophytin (Pheo)
What is the result of photooxidation?
This separation of charge creates a positively charged chlorophyll molecule (Chl1* → Chl+) and a negatively charged acceptor molecule (Pheo → •Pheo-).
True or False: Chlorophylls a and b have two absorbance peaks at the same ends of the solar spectrum.
False, opposite end of the spectrum
Carotenoids, such as β-carotene, absorb in the ______ range, which is why they appear ______(reflected light).
blue, orange
The phycobilins absorb light in the middle of the solar spectrum and are primarily found in ______ photosynthetic organisms.
Marine
______ functions as a solar panel that harvests light energy for PSII and PSI reaction centers in the thylakoid membrane.
LHC II
A series of ______ reactions passes the energy along to LHC I surrounding the reaction centers, where photooxidation takes place.
Resonance-energy
The ______ of electron flow in the photosynthetic electron transport system illustrated the redox energy made available by light absorption at reaction center complexes is used to establish a proton gradient across the thylakoid membrane and to reduce NADP+.
Z-scheme
The Z-scheme is an example of a ______ electron transfer.
Noncyclic
When electrons move from ferredoxin back to the cytochrome b6f complex, it is known as ______ electron transfer.
Cyclic
True or False: In cyclic electron transfer, it produces more ATP and less NADPH.
True
True or False: Components of the photosynthetic electron transport systems in bacteria resemble those in plant chloroplasts, suggesting an evolutionary relationship.
True
The photosynthetic electron transport systems in purple bacteria (PSII-like) and green sulfur bacteria (PSI-like) use ______ pathways to oxidize organic or inorganic substrates rather than H2O.
anoxygenic
______ and plant chloroplasts are similar in that they both use oxygenic photosynthetic pathways (oxidize H2O to generate O2).
Cyanobacteria
True or False: In cyanobacteria, they use use cytochrome b6f, cytochrome c6 and plastoquinone for both oxidative phosphorylation and photophosphorylation.
True
In cyanobacteria oxidative phosphorylation, electrons flow from ______ to ______.
NADH –> O2
In photophosphorylation, electrons flow from ______ to ______.
H20 —-> NADP+
Both processes are accompanied by proton movement across the membrane, known as a ______ cycle.
Q
How do electrons flow through in electron carriers in PS II? (slide 20)
Electrons extracted from H2O
- —> OEC
- –> Tyr(z)
- –> P680 (photooxidation)
- –> Pheo
- –> PQ(a)
- –> PQ(b)
- –> PQ(b)H2 (diffuses through thylakoid membrane to deliver e- to Cytb6f)
How many electrons does it take to reduce 2 PQB to 2 PQBH2.
4
In the PQ cycle, ______ H+ are translocated by the combined reactions in PSII and cytochrome b6f and An additional ____ H+ are generated by the oxidation of 2 H2O to form O2, leading to a net gain of ____ H+ in the thylakoid lumen.
8, 4, 12
How do electrons flow through in electron carriers in PS I? (slide 22)
PC —> into two separate pathways that are the same
- –> P700 (photooxidation)
- –> Chl
- –> ChlA0
- –> Phylloquinone
- –> Fx (both pathways meet here)
- –> Fa
- –> Fb
- –> ferrodoxin
- –> ferredoxin-NADP+ reductase
True or False: The electrons from ferredoxin are used to reduce the FAD moiety in ferredoxin-NADP+ reductase, which then reduces NADP+ to form NADPH in the stroma.
True
True or False: Cyclic photophosphorylation between PSI and cytochrome b6f generates an electrochemical proton gradient independent of H2O oxidation and NADP+ reduction.
True
What occurs when NAD+ levels are limiting?
Photooxidation of chloroplast P700 leads to electron flow between ferredoxin and the plastoquinone pool (PQ cycle), resulting in proton translocation by cytochrome b6f and ATP synthesis.
In mitochondria and bacteria, protons are pumped ______ of the organelle or cell, and F1 is on the ______ of the membrane; in plant thylakoids, protons are pumped ______ the flattened discs within chloroplasts, and CF1 is on the ______ of the disc membrane.
out, in
into, outside
True or False: Exactly the same mechanism of energy conversion (from proton gradient to ATP) occurs in mitochondria, chloroplasts and bacteria.
True
ATP is synthesized in the ______ of mitochondria, the ______ of chloroplasts, and the ______ of bacteria.
matrix, stroma, cytosol
The Calvin cycles converts triphosphates into hexose phosphates, the building blocks for what three primary carbohydrates in plant cells?
Starch, sucrose and cellulose
Pentose phosphates are Calvin cycle intermediates and also form? .
Carbohydrate backbone for DNA and RNA.
What is stage 1 of the calvin cycle?
Ribulose-1,5-bisphosphate (RuBP), a C5 molecule, is combined with CO2 in a reaction catalyzed by rubisco to form a transient C6 molecule, which is rapidly cleaved into two C3 molecules of 3-phosphoglycerate
What is stage 2 of the calvin cycle?
3-phosphoglycerate is reduced to glyceraldehyde-3-phosphate in reactions involving ATP and NADPH
What is stage 3 of the calvin cycle?
5 glyceraldehyde-3-phosphate (5 x C3) are used to resynthesize 3 ribulose-1,5-bisphosphate (3 x C5) in a series of “carbon shuffle” reactions that require ATP.
Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate are used in the stroma to synthesize ______ for energy storage
Starch
Glyceraldehyde-3-phosphate and dihydroxyacetone are transported into cytosol where they are used to synthesize ______ for export to plant tissues or catabolized by ______ for energy conversion.
Sucrose, glycolysis
What enzyme converts glyceraldehyde-3-phosphate and dihydroxyacetone?
Triose phosphate isomerase
What enzyme converts What enzyme converts glyceraldehyde-3-phosphate and dihydroxyacetone simpler glucose and fructose molecules?
Aldolase
The ______ cycle in plants provides a mechanism for fats stored in seeds to be converted to sucrose for export to developing plant tissues prior to the onset of photosynthesis.
Glyoxylate
Two unique glyoxylate cycle enzymes, ______ and ______, are localized to cell organelles called glyoxysomes in plant cells.
isocitrate lyase, malate synthase
______ serves as the central metabolic intermediate in this pathway by transporting the four carbons obtained from two acetyl-CoA molecules to the mitochondria, where ______ is converted to malate for use in the citrate cycle or for export to the cytosol.
Succinate (x2)
