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MSDF > Photosystem II > Flashcards

Photosystem II Flashcards

1
Q

What is PsII related to?

A

Purple bacteria reaction centre

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2
Q

What are the main subunits of PSII reaction centre?

A

D1 and D2 polypeptides

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3
Q

What is the structure of D1/D2 polypeptides of PsII?

A

each have 5 transmembrane helices

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4
Q

What are the cofactors in PSII?

A
  • 4 chlorophylls
  • 2 pheophytins
  • 2 plastoquinones
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5
Q

What are the differences between PSII and PBRC?

A
  • 2 chlorophylls are further apart
  • Contains MnCaO5 cluster
  • Chlorophyll absorbs red and blue light
  • Chlorophylls more extreme oxidising and reducing
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6
Q

How is the MnCaO5 cluster of PSII electrically conected to chlorophylls?

A

By a tyrosine residue

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7
Q

What is the excited state of PSII?

A

p680*

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8
Q

Once the singlet excited state in PSII has been formed what happens?

A
  • Causes movement of an electron across the membrane
  • Forming p680+ and PQ-
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9
Q

What happens once p680+ has been formed in PSII?

A

p680+ oxidises Tyr sidechain forming Tyrz+

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10
Q

Once the tyrosine has been oxidised what occurs?

A

Tyrosin cation oxidises the MnCaO5/(H2O)2 cluster, removing 1 electron

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11
Q

What does 1 photon in PSII power?

A

The movement of one electron from Mn4CaO5/(H2O)2 cluster to PQB plastoquinone

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12
Q

What occurs as a result of the 2nd light powered electron translocation?

A
  • PQ- is reduced to PQH2
  • PQH2 dissociates from QB binding site and is replaced by PQ
  • 2nd electron is removed from Mn cluster
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13
Q

After 2 further light-powered electron translocations what occurs in PSII?

A
  • A 2nd PQH2 is produced on one side of membrane
  • On other side 4 electrons have now been removed from Mn cluster
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14
Q

Where do the electrons get removed from the Mn4CaO5 cluster in PSII?

A

The 2 water molecules bound

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15
Q

What redox states can Mn be in?

A

+3, +4, +5

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16
Q

What happens after the removal of the 4th electron from the Mn cluster in PSII?

A
  • Triggers the release of oxygen
  • 2 new water molecules bind
17
Q

What core antenna proteins is the D1/D2 reaction centre associated with?

A

CP43 and CP47

18
Q

What is the structure of CP43 and CP47?

A

Membrane proteins containing carotenoids and chlorophylls

19
Q

Besides CP43 and CP47 what also makes up the light harvesting complex of PSII?

A
  • LHCII trimers
  • CP29 and CP26 minor proteins
20
Q

How is excitation energy transferred from one LHCII to another in PSII?

A

Via CP43 and 47 with help from CP26 and CP29

21
Q

What is the structure of LCHII of PSII?

A
  • Trimer
  • Each monomer contains 3 alpha helices and multiple chlorophyll a and b
  • Contains carotenoids

MSDF (30 decks)

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