Oxidative Phosphorylation

Question 1

What delivers the electrons to the electron transport chain?

Answer 1

NADH, created by the TCA

Question 2

What two things determine Eh?

Answer 2

1. The Em value (the lower the Em, the lower the Eh)

2. The [red]/[ox] ratio (the higher the ratio, the lower the Eh)

Question 3

What are the properties of Quinones?

Answer 3

• membrane soluble redox carrier
• can go from fully oxidised to semi to fully reduced (adding e- at a time)
• are hydrophobic so can be inside the membrane (hydrophobic isoprenoid sidechains)

Question 4

How many electrons do dinucleotides accept/donates?

Answer 4

2

Question 5

What is the basic structure of dinucleotides?

Answer 5

contains a nictotinamide ring which is where redox occur

Question 6

How does UQ catalyse its redox reaction

Answer 6

• has to associate with a protein

- attached tightly

Question 7

Does the semiquinone form detach from the protein? Why?

Answer 7

No, usually remains protein bound

• if they do dissociate from the protein, they become free radicals
• in tissues this may lead to disease such as Alzheimers

Question 8

Name the biological electron carriers?

Answer 8

substrates and metabolites:
- pyruvate/lactate
dinucleotides:
- NAD+/ NADH
-NADP+/NADPH
quinones:
- ubiquinone/ ubiquinol
flavins:
- FMN/FMNH2
transition metals:
- CU2+/ Cu1+

Question 9

How many electrons can be accepted/donated by Flavins?

Answer 9

2 e and 2 H can be added in one step, to go fully reduced

- can have semiquinone states

Question 10

Which type of Haem is a type of cytochrome?

Answer 10

Haemc1

Question 11

What is cytochrome Haemx?

Answer 11

electron shuttle

Question 12

What is the most common type of iron-sulphur cluster?

Answer 12

Fe1S0Cys4

• Single iron species (Fe2+/3+)
• surrounded by 4 cysteines
• Cysteinal sulfurs (no inorganic sulfurs)

Question 13

What are the 3 types of iron clusters in the ETC? Draw them.

Answer 13

Fe1S0Cys4
Fe2S2Cys4
Fe4S4Cys4

Question 14

What are the properties of the Fe2S2Cys4 cluster?

Answer 14

2 Tetrahedral irons
2 inorganic sulphurs
4 Cysteine side chains
- the transferring electron is delocalised across the whole Fe2S2 cluster

Question 15

How many electrons can the iron clusters accept each?

Answer 15

Only one at a time

Question 16

What are the properties of the Fe4S4Cys4 cluster?

Answer 16

4 Tetrahedral irons
4 inorganic sulphurs
4 Cysteine side chains
- orbitals overlap
- the transferring electron is delocalised across the whole cluster
- re-organisation energy, energy is minimised by closing the shape

Question 17

What influences the mid point potential of an iron sulphur complex?

Answer 17

• environment within the protein structure

Question 18

What does a low Eh mean?

Answer 18

more likely to donate electron

Question 19

What are the different ways electrons can be transferred in biological systems?

Answer 19

1. electrons transferred intermolecularly
   - electron transfer from donor substrate to acceptor cofactor
2. electrons transferred intramolecularly
   - electron jumping between different cofactors in the same protein
   - electron jumping from one protein to another

Question 20

Does distance have a strong influence on the rate that the electrons will be transferred?

Answer 20

Yes. The further apart electrons are, the slower the rate.

Question 21

What is the key parameter to use for measuring distance between atoms or cofactors?

Answer 21

edge-to-edge distance

- electrons do not sit at the centre of the atom/ can be delocalised across the cofactor