PS2 (lect 4)

Question 1

Why can PS2 hydrolyse water?

Answer 1

-P680+ is very oxidising so can abstract e- from water
-light provides energy

Question 2

What are the D1 and D2 subunits in PS2?

Answer 2

core RC subunits
-form heterodimers
-binds cofactors

Question 3

What are the CP43 and CP47 subunits in PS2?

Answer 3

core antenna subunits
-bind lots of chlorophylls and carotenes

Question 4

What does the PsbO subunit in PS2 do?

Answer 4

stabilises Mn-cluster

Question 5

What is the issue with the back reaction in PS2?

Answer 5

energy gap between PQa and PheD1 is smaller so e- can be transferred backwards
-forms harmful triplet states and singlet oxygens!

Question 6

What is responsible for non-photochemical quenching to protect PS2?

Answer 6

Plants: xanthophyll cycle
Cyanobacteria: carotenoids (in phycobilisomes)

Question 7

What does the manganese cluster in the oxygen evolving complex do?

Answer 7

Couples RC e- transfers to water oxidation

-Gathers 4+ charge from 4 successive charge separation events (RC e- transfer to PQ)
-Oxidises 2 waters (these provide 4e- which resets it!)