Reaction centres and Electron Transfer

Question 1

What is the terminal donor of electrons in photosynthesis?

Answer 1

Water

Question 2

What is the terminal acceptor of electrons in photosynthesis?

Answer 2

NADP+

Question 3

What is the primary electron donor in photosystem II?

Answer 3

Chlorophyll p680

Question 4

How can chlorophyll be excited?

Answer 4

Either

• by absorbing a photon of the correct energy (e.g. 680)
• Surrounding pigments transfer an electron of the correct energy via FRET

Question 5

What does the formation of p680* trigger?

Answer 5

A transmembrane electron transfer reaction

Question 6

Where does the electron from p680* get transferred to?

Answer 6

Q_B site where is reduces the plastoquinone

Question 7

Which side of the membrane is the Q_B complex on?

Answer 7

The stromal side

Question 8

In total how many electrons and protons can plastoquinone bind and collect?

Answer 8

2e^-, 2H⁺

Question 9

What is formed by the electron transfer from p680*?

Answer 9

p680⁺

Question 10

How is p680⁺ re-reduced?

Answer 10

By an electron from a redox active tyrosine

Question 11

What re-reduces the tyrosine molecule in photosystem II?

Answer 11

By an electron derived from a water molecule

Question 12

In photosystem II what catalyses the oxidation of water?

Answer 12

A cluster of 4 Mn ions

Question 13

What metal is also found in the Mn cluster of photosystems?

Answer 13

Ca

Question 14

Overall in photosystem II what has the energy of 1 photon been used for?

Answer 14

To reduce a quinone on one side of the membrane and to partially oxidise water on the other side of the membrane

Question 15

At the Q_B site how many plastoquinones are reduced?

Answer 15

2

Question 16

How many electrons are required at the Q_B site to reduce 2 plastoquinones?

Answer 16

4 e^- delivered sequentially

Question 17

The reduction of 2 plastoquinones to 2 plastoquinols results in how many H+ being taken up from the stroma?

Answer 17

4

Question 18

How many p680+ are generated from reduction of quinones?

Answer 18

4

Question 19

The 4 p680+ generated will allow how many oxygen atoms and H+ to be released?

Answer 19

• 2 oxygen atoms
• 4H+

Question 20

H+ produced from oxidation of water in photosystem II are moved where?

Answer 20

Into the thylakoid membrane

Question 21

What happens to the plastoquinol produced?

Question 22

What is the function of the cytochrom bf complex?

Answer 22

Oxidises plastoquinol and uses the electrons produced to reduce a plastocyanin

Question 23

What accompanies plastoquinol oxidation?

Answer 23

Proton release into the thylakoid lumen

Question 24

What metal does plastocyanin contain?

Answer 24

Copper

Question 25

Outline the structure of plastocyanin

Answer 25

• small water soluble protein
• the copper redox centre carries one electron

Question 26

Where is plastocyanin located?

Answer 26

In the thylakoid lumen

Question 27

In photosystem I what is the primary donor?

Answer 27

A chlorophyll dimer called p700

Question 28

What does formation of p700* trigger?

Answer 28

A transmembrane electron transfer reaction

Question 29

Where does F_B pass an electron to?

Answer 29

Ferredoxin

Question 30

Where is ferredoxin located?

Answer 30

In the stroma

Question 31

What re-reduces p700+?

Answer 31

plastocyanin

Question 32

In photosystem I how is an electron transferred across the membrane?

Answer 32

Via chlorophyll, quinone, and FeS centre redox components

Question 33

What is the structure of the redox centre of F_B?

Answer 33

Fe₄S₄

Question 34

What is the function of the enzyme FNR?

Answer 34

Transfers electrons from ferredoxin to NADP+

Question 35

What 2 steps of photosynthesis require energy input?

Answer 35

• Formation of the p680 excited state
• Formation of the p700 excited state