Reaction centres and Electron Transfer Flashcards
What is the terminal donor of electrons in photosynthesis?
Water
What is the terminal acceptor of electrons in photosynthesis?
NADP+
What is the primary electron donor in photosystem II?
Chlorophyll p680
How can chlorophyll be excited?
Either
- by absorbing a photon of the correct energy (e.g. 680)
- Surrounding pigments transfer an electron of the correct energy via FRET
What does the formation of p680* trigger?
A transmembrane electron transfer reaction
Where does the electron from p680* get transferred to?
QB site where is reduces the plastoquinone
Which side of the membrane is the QB complex on?
The stromal side
In total how many electrons and protons can plastoquinone bind and collect?
2e-, 2H+
What is formed by the electron transfer from p680*?
p680+
How is p680+ re-reduced?
By an electron from a redox active tyrosine
What re-reduces the tyrosine molecule in photosystem II?
By an electron derived from a water molecule
In photosystem II what catalyses the oxidation of water?
A cluster of 4 Mn ions
What metal is also found in the Mn cluster of photosystems?
Ca
Overall in photosystem II what has the energy of 1 photon been used for?
To reduce a quinone on one side of the membrane and to partially oxidise water on the other side of the membrane
At the QB site how many plastoquinones are reduced?
2
How many electrons are required at the QB site to reduce 2 plastoquinones?
4 e- delivered sequentially
The reduction of 2 plastoquinones to 2 plastoquinols results in how many H+ being taken up from the stroma?
4
How many p680+ are generated from reduction of quinones?
4
The 4 p680+ generated will allow how many oxygen atoms and H+ to be released?
- 2 oxygen atoms
- 4H+
H+ produced from oxidation of water in photosystem II are moved where?
Into the thylakoid membrane
What happens to the plastoquinol produced?
What is the function of the cytochrom bf complex?
Oxidises plastoquinol and uses the electrons produced to reduce a plastocyanin
What accompanies plastoquinol oxidation?
Proton release into the thylakoid lumen
What metal does plastocyanin contain?
Copper
Outline the structure of plastocyanin
- small water soluble protein
- the copper redox centre carries one electron
Where is plastocyanin located?
In the thylakoid lumen
In photosystem I what is the primary donor?
A chlorophyll dimer called p700
What does formation of p700* trigger?
A transmembrane electron transfer reaction
Where does FB pass an electron to?
Ferredoxin
Where is ferredoxin located?
In the stroma
What re-reduces p700+?
plastocyanin
In photosystem I how is an electron transferred across the membrane?
Via chlorophyll, quinone, and FeS centre redox components
What is the structure of the redox centre of FB?
Fe4S4
What is the function of the enzyme FNR?
Transfers electrons from ferredoxin to NADP+
What 2 steps of photosynthesis require energy input?
- Formation of the p680 excited state
- Formation of the p700 excited state
