Purple Bacteria Reaction Centre

Question 1

Why do anoxygenic photosynthetic bacteria have extensive membranes to house photosynthetic apparatus?

Answer 1

Allows organisms to pack their cells with ligh harvesting pigments

Question 2

What are the cofactors in R.Sph reaction centre?

Answer 2

• 4 bacteriochlorophyll
• 2 bacteriopheophytin
• 2 ubiquinones
• 1 Fe atom
• 1 carotenoid

Question 3

What is the purpose of the carotenoid in R.Sph reaction centre?

Answer 3

It is photoprotective

Question 4

What do 2 of the Bch of the R.Sph reaction centre do?

Answer 4

• Form a dimer called p870
• this exhibits excitomic coupling and effectively acts as one molecule

Question 5

How is the r.Sph reaction centre arranged?

Answer 5

In 2 branches related by the same axis of 2 fold symmetry

Question 6

Which branch do electron take in PBRC (purple bacteria reaction centre)?

Answer 6

A branch

Question 7

How are cofactors held in place in PBRC?

Answer 7

By a protein scaffold made up from L and M polypeptides

Question 8

What is the structure of L + M polypeptides in PBRC?

Answer 8

• Each made up of 5 transmembrane helices
• Related by an axis of 2 fold symmetry that runs perpendicular to plane of membrane

Question 9

Which branch is the carotenoid in PBRC positioned close to?

Answer 9

B

Question 10

Which Ubiquionone acts as a mobile carrier to take electrons to the Cyt B1 complex in PBRC?

Answer 10

UQ B

Question 11

What acts as a cap to the PBRC?

Answer 11

H single transmembrane helix domain

Question 12

What is the purpose of the PBRC?

Answer 12

To use light energy to separate electrical charge charge across membranes, leaving -ve on one side and +ve on the other

Question 14

What triggers the PBRC?

Answer 14

Formation of the 1st singlet electronic excited state on p870

Question 15

How is p870 excited?

Answer 15

Through resonance energy transfer of BCh1s of LHC

Question 16

What triggers electron transfer across the membrane in PBRC?

Answer 16

p870* converting BCh into a strong reductant

Question 17

Where does p870* transfer electrons to?

Answer 17

Monomeric BCH₁

Question 18

What is the result of electron transfer in PBRC?

Answer 18

• p870+ (cationic state)
• anionic Q_A (UQ-) on other side of membrane

Question 19

How is UQ- at Q_A oxidised in PBRC?

Answer 19

By electron transfer to Q_B

Question 20

What reduced p870+ in PBRC?

Answer 20

Water soluble cytochrome C₂

Question 21

After the second light induce charge separation what happens at Qb of the PBRC?

Answer 21

• Double reduction of ubiquinone at Q_B
• Uptake of 2H+ to form ubiquinol (UQH₂)

Question 22

The energy of how many photons makes 1 UQH₂ in PBRC?

Answer 22

2

Question 23

2 photons oxidise how many 3+ cytochrome C₂ in PBRC?

Answer 23

2