4 Flashcards
Fates of Excited electrons? 3•
•Fluorescence: They eventually return to a lower energy state
•Resonance: transfer of energy (not electrons) between adjacent pigments
•Photochemistry (redox reactions): transfer of electrons to acceptor molecules. Pigments become oxidized, acceptor molecules become reduced.
Antenna complex?
Contains pigment molecules that capture and direct energy from protists towards the reaction Center. Both chlorophylls have it.
Plants can adjust how much light they get. How?
They adjust the concentration of chlorophyll.
When does photochemistry commonly occur?
When electrons go from the photosystem (gets oxidized) and travels to the electron acceptor (gets reduced).
Reaction center 2 vs reaction center 1?
RC2: Accepts electron from protons produced from the splitting of water, and that electron flows to Pheophytin, which reduces pheophytin.
RC1: Accepts electron from photosystem 2 to RC1, and brings that electron to Ferredoxin, which reduces it.
How does reaction center 2 obtain the electron after being oxidized?
From the splitting of water which a proton releases an electron and travels to reaction center 2, which then travels to pheophytin.
How does reaction center 1 reobtain an electron after being oxidized?
The electron comes from reaction center 2.
How many electrons get passed to photosystem 2 and 1?
1 electron, even if it shows more.
The linear scheme (Z-scheme) of photosystem?
The shape of arrows representing the amount of energy through ETC, it looks like the letter, Z. However, there is higher energy when electron is at photosystem 1 (P700) than photosystem 2 (P680).
Photosystem 2 not only passes the electron in photosystem 1, but does something else?
Pumps protons and electrons from the stroma to the lumen to contribute to the electrochemical gradient.
Plastoquinone (PQ)?
Transports protons from the stroma to the lumen, and transports electrons from photosystem 2 to 1.
The ATP produced by the chloroplast is ONLY used by?
The chloroplast
Plastocyanin (PC)?
Electron carrier that links PS2 to and PS1 by donating electrons from PS2 to the reaction center of PS1.
Cyclic scheme of photophosphorlyation?
Instead of electrons flowing through the Z-scheme, it goes back to PQ after going through PS I since plants don’t always need NADPH but still needs ATP.
It will also follow that scheme to avoid excess O2 accumulation from PS II.
Where does the Calvin cycle occur?
In the stroma.
Three steps of Calvin cycle? 3•
•Carbon fixation
•Reduction
•Substrate Regeneration
How many cycles to get 1 G3P?
3
G3P two fates?
•20% of it go to make glucose
•80% of it goes to regenerate the substrate -> RuB
RubisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase)?
An enzyme that catalysis the reaction of carbon fixation.
There is a competition between O2 and CO2 at the active site of RubisCO. What happens?
RubisCO catalysis two opposite competing reactions, one with CO2 (carbon fixation) and the other with O2 (photorespiration).
At the end of photorespiration, what is produced?
Oxidation of PGA to PG and heat.
Does photorespiration contribute to the Calvin cycle?
No, only carbon fixation.
RubisCO has a very slow reaction rate and low ______ binding affinity?
CO2
Why is RubisCO such a poor catalyst?
•Competition of catalyzing either CO2 or O2
•Very low reaction rate
•Low CO2 binding affinity
How do photosynthetic organisms cope with a poor C-fixing catalyst? •2
•Synthesizing a lot of RubisCO
•Concentrating CO2 around RubisCO (C4 and CAM carbon concentrating mechanisms make photosynthesis more efficient)
C4 Plants?
One CO2 molecule inside the mesophyll cells become phosphoenolpyruvate (PEP) which then becomes 4 carbon organic acids, malate. This is supported by the enzyme, PEP Carbonxylase. Malate travels to the bundle sheath cells and goes next to rubisco. Malate breaks down into pyruvate and CO2 ensuring that it brings a high concentration of CO2 next to the rubisco.
How do molecules get transported within the plant organism?
Through a channel called a Plasmodesmata that connects the cytosols between cells.
Malate (4 carbons compound) to shuttle CO2 to the bundle sheath cells. It requires more/less ATP?
More
Crassulacean acid metabolism (CAM)?
In CAM, Rubisco activity occurs in the mesophyl cells. CO2 is converted to Crassulacean Acid trapped in a vacuole during the night. During the day, the Calvin cycle starts by releasing a high concentration of CO2 near rubisco.
When the electron acceptor (Pheophytin and Ferredoxin) become reduced, electromagnetic energy is transformed to?
Chemical energy.
How many cycles required to fix one CO2 molecule?
1
C3 photosynthesis?
The build of the 3-PGA molecule after carbon fixation since 3-PGA has three carbons.
Carbon Fixation reaction?
3RuBP + 3CO2 -> 6 3-PGA, catalyzed by Rubisco
Reduction reaction?
6 3PGA + 6ATP + 6NADPH -> 5 G3P (to regeneration) + 1 G3P (for glucose formation)
Regeneration formula?
5 G3P + 3ATP -> 3RuBP
In C4 photosynthesis, where is the Calvin cycle located?
The bundle sheath cell under the mesophyll cell.
In C3 photosynthesis, where does the Calvin cycle occur?
Inside the mesophyll cell.
Why is CAM important?
This is so CO2 can ONLY enter the plant at night, during colder temperatures and less dehydration (stomata open). However at night, they can keep their stomata closed to reduce the chances of dehydrating.
How does electromagnetic energy get converted into chemical energy?
Light gets absorbed by the pigments in the antenna complex, which then transfers it to two specialized chlorophyll molecules in the reaction center, energizing the pigment and exciting that electron. However, electrons in its excited state must transfer their energy via resonance as soon as possible. It reduces the electron acceptor, increases potential energy, which creates chemical energy.
How does cyclic electron flow affect PSII?
Since its the same electron bouncing around PSI, a new electron is not needed and PSII halts.
