Light-driven Proton Transport Flashcards
What do reaction centres do?
convert light energy into potential redox energy by absorbing a photon and exciting a photosensitive pigment
Describe the structure of chlorophyll.
cyclic tetrapyrrole
Mg centre
Describe the structure of pheophytin.
cyclic tetrapyrrole protonated centre (2H)
Describe the structure of plastoQUINONE.
phenol ring
2 carbonyl O
Describe the structure of plastoQUINOL.
phenol ring
2 -OH groups
(reduced form)
Cyclic e- transport is mainly done by…
purple bacteria
Non-cyclic e- transport is mainly done by…
green plants
Describe the structure of the reaction centre of purple bacteria (Rhodobacter).
~ 3 polypeptides (H, M, L) ~ redox centres: 4 chlorophyll 2 bacteriopheophytins (BPh) 2 quinines
What is the difference between the excited state and the electro+ve state?
200KJ/mol
How is light absorption maximised?
~ the light harvesting complexes around the reaction centres increase light capture by 100x
~ they funnel the protons captures to the reaction centre
DELOCALISATION EXCITATION COUPLING
Which pigments does LH1 contains in Rhodobacter?
24 chlorophyll
24 carotenoid pigment
Which pigments does LH2 contains in Rhodobacter?
18 chlorophyll
9 carotenoid pigment
stroma lamellae
connectors between grana stacks that contain ATP synthase in their membranes
Describe the role of Mn centres.
~ O2 evolution occurs here
~ binds water & releases e- then donates them to P680 in PSII
In the mitochondria, P and N are…
P = intermembrane space N = matrix/lumen
In the chloroplasts, P and N are…
P = thylakoid membrane lumen N = stroma
Compare the electrochemical gradients (EG) in mitochondria and chloroplasts.
~ magnitude is equal as they have opposite polarity
~ in MIT, main part of EG is the ELECTRICAL GRADIENT across the membrane
~In CHLORO, main part of EG is the CHEMICAL GRADIENT across membrane
Why does the __ make up the biggest part of the electrochemical gradient in MITOCHONDRIA?
~ electrical gradient
- because proton transport is coupled to substrate transport by electro-neutral transporters
- this dissipates the chemical grad. leaving big electrical grad
Why does the __ make up the biggest part of the electrochemical gradient in CHLOROPLASTS?
~ proton chemical gradient
- the thylakoid membrane is permeable to other ions
- acts as SHUNT CONDUCTANCE –> allows large H+ influx = substantial pH gradient
For every 2e- pumped through the non-cyclic photosynthesis cycle, how many H+ are also pumped?
6
~ 2 from water splitting
~ 4 from Q cycle
What difference is there from having P680 rather than P870?
P680 is in plants
P870 is in bacteria & is less electro+ve so cannot accept e- from water splitting
How do you prove that the pH gradient across thylakoid membrane drives ATP synthase?
Jagendorf (1966) did an experiment:
1. isolate thylakoid membranes in a test tube
2. incubate in the dark & low pH
3. add ADP + Pi solution & change pH to 8
RESULT: change in pH = ATP synthesis to occur in dark