Photosystem I Flashcards
What is the overall structure of PSI?
- Trimer
- Symmetry axis with branches of cofactors spanning the membrane
What cofactors does PSI contain?
- 100 chlorophyll a
- 2 phyloquinones
- 3 FeS clusters
What makes up the PSI reaction centre?
PsaA, PsaB, PsaC
How many subunits do PsaA and PsaB of PSI contain?
11
How many helices are in the c terminal domains of PsaA and PsaB?
5
How many helices are in the N terminal domains of PsaA and PsaB?
6 helices
How many chlorophylls do the N terminal PsaA and PsaB subunits bind to?
45
What does the extra membrane PsaC polypeptide bind in the PSI reaction centre?
FA and FB Fe4S4
In the PSI reaction centre what do PsaA and PsaB bind to?
- p700
- A0 and A1
- Fx Fe4S4 cluster
What is the structure of the PSI Fe4S4 clusters?
Each iron atom is bound to 3 inorganic sulfurs and 1 cysteine sulfur
What is the primary acceptor of electrons in PSI?
p700, a dimer of two chlorophyll a
What does formation of p700* trigger in PSI?
Transmembrane electron transfer to the FB Fe-S centre
Formation of p700* in PSI is usually the result of what?
Resonance energy transfer from antenna chlorophylls/carotenoids
In PSI which branch does electron transfer proceed upon?
Either branch
Moving an electron from p700 to FB results in the formation of what?
p700+ and FB-
Are H+ translocated when an electron moves from p700?
No
What re-reduces p700+ in PSI?
Plastocyanin
Where does plastocyanin in PSI collect its electron from?
Cytochrome bf
In PSI what oxidses FB-?
Ferredoxin
Once ferredoxin has oxidised FB-what does it do?
Carries an electron to FNR and transfers 2 electrons from 2 ferredoxins to NADP+
What is generated at FNR?
NADPH
How many electrons does the formation of 2NADPH in PSI require?
4
How many photons does the formation of 2NADPH in PSI require?
4
What is the NADPH produced by FNR in PSI used for?
Biosynthesis in ‘dark’ reactions
What is the peripheral antenna of PSI called?
LHCI
What makes up LHCI of PSI?
4 types of light harvesting protein LHCa1-4
8 photons causes the transfer of how many electrons from H2O to NADP+?
4 electrons
What reaction occurs as a result of absorption of 8 photons?
8 photons + 2H2O + 2NADP+ → O2 + 2NADPH + H+ translocated