Oxidative Phosphorylation

Question 1

What happens during oxidative phosphorylation?

Answer 1

Electrons are transferred through electron carriers

Process generates a proton gradient for ATP synthase

Question 2

Where does oxidative phosphorylation take place?

Answer 2

Inner mitochondrial membrane

Question 3

More acidic in the ___________

Answer 3

Intermembrane space

Question 4

What are 4 examples of electron carriers?

Answer 4

• NAD and FAD
• Ubiquinone/Coenzyme Q
• Cytochromes
• Iron-sulphur proteins

Question 5

What are the properties of ubiquinone/coenzyme Q?

Answer 5

• Fat-soluble so able to move through membrane

- Can accept 1 or 2 electrons

Question 6

What are cytochromes?

Answer 6

Iron heme-containing proteins that act as an electron carrier

Question 7

What are the 3 types of cytochromes involves in oxidative phosphorylation? Are they membrane-bound or soluble?

Answer 7

1. A is membrane-bound
2. B is membrane-bound
3. C is soluble

Question 8

What is the basic formation of iron-sulphur proteins?

Answer 8

Fe and S coordinates with 4 cysteine residues from a protein

Question 9

Complex I: where are the electrons transferred?

Answer 9

NADH to ubiquinone

Question 10

Structure of complex I

Answer 10

• 42 polypeptide chains

- 6 iron-sulphur centres

Question 11

What is formed at complex I and where does it diffuse to?

Answer 11

Ubiquinol diffuses to complex III

Question 12

Complex II: where are the electrons transferred?

Answer 12

Succinate to ubiquinone

Question 13

What happens at complex II?

Answer 13

Electron is removed from succinate and transferred to FAD then to ubiquinone to form ubiquinol

Question 14

Complex III: where are the electrons transferred?

Answer 14

Ubiquinone to cytochrome c

Question 15

What is the problem with the reaction at complex III and how is it overcome?

Answer 15

Cytochrome c can only accept 1 electron but ubiquinone donates 2 electrons so there’s a process called the Q cycle

Question 16

What is the Q cycle?

Answer 16

1 electron is transferred to cytochrome c and the other electron is recycled through the complex forming semi-ubiquinone

Question 17

Complex IV: where are the electrons transferred?

Answer 17

Cytochrome c to O2

Question 18

What is the relation between the inter membrane space and complex I and IV?

Answer 18

4 protons are pumped into the inter membrane space

Question 19

What is formed at complex IV?

Answer 19

H2O

Question 20

During the formation of H2O in Complex IV of oxidative phosphorylation what is consumed? What is the significance of this?

Answer 20

• 4 protons are consumed from inside the mitochondria

- This helps to amplify the proton gradient across the inner mitochondrial membrane

Question 21

What does ATP synthase act as a pore for?

Answer 21

Hydrogen ions

Question 22

What are the subunits of ATP synthase and what are their functions?

Answer 22

F1 - ATPase for formation

F0 - membrane-embedded portion which acts as a pore for protons to pass through to drive ATPase

Question 23

What makes up the F1 subunit?

Answer 23

ß units, present in 3 states

Question 24

What are the 3 states of the ß units?

Answer 24

Empty
ADP
ATP

Question 25

What is bound at each state of the ß units?

Answer 25

Empty - nothing bound ADP - ADP and Pi bound, loose ATP - ATP-bound, tight configuration

Question 26

How does the movement of protons through ATP synthase drive ATP formation?

Answer 26

- As the protons pass through the F0 complex they cause the subunits to rotate by 1/3 - Each 1/3 turn causes a conformational change in the Beta subunit of F1 ATPase

Question 27

What regulates oxidative phosphorylation?

Answer 27

ADP and ATP levels

Question 28

How is oxidative phosphorylation regulated at rest?

Answer 28

The proton motive force is high but due to high ATP levels | --> minimal flow of protons through ATP synthase and low transfer of electrons

Question 29

How is oxidative phosphorylation regulated during exercise?

Answer 29

ATP is consumed therefore ADP levels rise --> proton movement through synthase discharging the proton motive force. Results in increase electron transfer to keep proton motive force

Question 30

What are the two types of inhibitors of oxidative phosphorylation?

Answer 30

- Electron transport inhibitor | - Uncoupling agents

Question 31

Give an example of an electron transport inhibitor and how it works

Answer 31

Cyanide, stops carriers from receiving electrons

Question 32

Give an example of an uncoupling agent and how it works

Answer 32

2,4-Dinitrophenol, dissipates the proton gradient so have to work harder to make ATP