Photosystem I

Question 1

What is the overall structure of PSI?

Answer 1

• Trimer
• Symmetry axis with branches of cofactors spanning the membrane

Question 2

What cofactors does PSI contain?

Answer 2

• 100 chlorophyll a
• 2 phyloquinones
• 3 FeS clusters

Question 3

What makes up the PSI reaction centre?

Answer 3

PsaA, PsaB, PsaC

Question 4

How many subunits do PsaA and PsaB of PSI contain?

Answer 4

11

Question 5

How many helices are in the c terminal domains of PsaA and PsaB?

Answer 5

5

Question 6

How many helices are in the N terminal domains of PsaA and PsaB?

Answer 6

6 helices

Question 7

How many chlorophylls do the N terminal PsaA and PsaB subunits bind to?

Answer 7

45

Question 8

What does the extra membrane PsaC polypeptide bind in the PSI reaction centre?

Answer 8

F_A and F_B Fe₄S₄

Question 9

In the PSI reaction centre what do PsaA and PsaB bind to?

Answer 9

• p700
• A₀ and A₁
• F_x Fe₄S₄ cluster

Question 10

What is the structure of the PSI Fe₄S₄ clusters?

Answer 10

Each iron atom is bound to 3 inorganic sulfurs and 1 cysteine sulfur

Question 11

What is the primary acceptor of electrons in PSI?

Answer 11

p700, a dimer of two chlorophyll a

Question 12

What does formation of p700* trigger in PSI?

Answer 12

Transmembrane electron transfer to the F_B Fe-S centre

Question 13

Formation of p700* in PSI is usually the result of what?

Answer 13

Resonance energy transfer from antenna chlorophylls/carotenoids

Question 14

In PSI which branch does electron transfer proceed upon?

Answer 14

Either branch

Question 15

Moving an electron from p700 to F_B results in the formation of what?

Answer 15

p700+ and F_B-

Question 16

Are H+ translocated when an electron moves from p700?

Answer 16

No

Question 17

What re-reduces p700+ in PSI?

Answer 17

Plastocyanin

Question 18

Where does plastocyanin in PSI collect its electron from?

Answer 18

Cytochrome bf

Question 19

In PSI what oxidses F_B-?

Answer 19

Ferredoxin

Question 20

Once ferredoxin has oxidised F_B-what does it do?

Answer 20

Carries an electron to FNR and transfers 2 electrons from 2 ferredoxins to NADP+

Question 21

What is generated at FNR?

Answer 21

NADPH

Question 22

How many electrons does the formation of 2NADPH in PSI require?

Answer 22

4

Question 23

How many photons does the formation of 2NADPH in PSI require?

Answer 23

4

Question 24

What is the NADPH produced by FNR in PSI used for?

Answer 24

Biosynthesis in ‘dark’ reactions

Question 25

What is the peripheral antenna of PSI called?

Answer 25

LHCI

Question 26

What makes up LHCI of PSI?

Answer 26

4 types of light harvesting protein LHCa1-4

Question 27

8 photons causes the transfer of how many electrons from H₂O to NADP+?

Answer 27

4 electrons

Question 28

What reaction occurs as a result of absorption of 8 photons?

Answer 28

8 photons + 2H₂O + 2NADP⁺ → O₂ + 2NADPH + H⁺ translocated