Oxidative Phosphorylation

Question 1

1) 3 ways of describing oxidation reactions

Answer 1

• add ‎O2 directly to the molecule
• remove an electron
• remove a pair of H atoms

Question 2

2) Which part of Nicotinamide Adenine Dinucleotide is involved in oxidation and reduction?

Answer 2

Nicotinamide ring

Question 3

3) Which part of Flavin Adenine Dinucleotide is involved in oxidation and reduction?

Answer 3

Flavin groups

Question 4

4) Where does oxidative phosphorylation take place and what is its function?

Answer 4

• In mitochondria of most tissues and cell types (not RBCs)

- ‘Energy trapping’ –> direct phosphorylation ADP –> ATP

Question 5

5) Where are the cytochrome components found?

Answer 5

• Buried in the inner membrane of mitochondria

Question 6

6) What are the 2 hydrogen pair acceptors?

Answer 6

• Flavin cofactors (FAD)

- Coenzyme Q / CoQ/ Ubiquinone

Question 7

7) What are the 2 electron acceptors?

Answer 7

• Iron sulfur proteins (cysteine on outside, can convert between Fe2+ and Fe3+)
• Cytochrome proteins (Haem ring is electron acceptor)

Question 8

8) Define oxido-reduction potential/ redox potential?

Answer 8

• Ability of carrier to donate its electrons to another electron acceptor molecule. Electrons move from carrier of more negative potential to carrier of more positive potential

Question 9

9) What type of reaction occurs when electrons are passed on?

Answer 9

• exergonic reactions (-delta G)

Question 10

10) State the order of oxidation/reduction carriers in the ETC.

Answer 10

• Flavin > CoQ > cytochrome b > cytochrome c > cytochrome a

Question 11

11) What are the redox values of NAD/NADH, FAD/FADH2 and O2/H2O?

Answer 11

NAD/NADH: -0.32V
FAD/FADH2: -0.20V
O2/H2O: +0.82V

Question 12

12) The transfer of protons creates which two gradients across the membrane?

Answer 12

• Concentration gradient (pH gradient)

- Voltage gradient (membrane potential)

Question 13

13) Describe the waterwheel analogy of ATP Synthase.

Answer 13

• Flow of water is H+ ions, wheel is ATP Synthase and movement/flow causes ATP production (rotational energy)

Question 14

14) Which reaction is necessary to reoxidise FADH2 to FAD for binding to ubiquinone in the ETC?

Answer 14

• (TCA Cycle) Succinate to Fumarate with succinate hydrogenase enzyme, in the inner membrane, as this produces FADH2 which can then be oxidised to FAD and bind to ubiquinone

Question 15

15) ATP yield of oxidative phosphorylation?

Answer 15

• NADH reoxidised = 2.5 ATP
• FADH2 = 1.5 ATP

= 4 ATP

Question 16

16) How does ATP and ADP concentrations affect the rate of O2 uptake? (described as respiratory control or ‘tightly-coupled’ oxidative phosphorylation)

Answer 16

• High [ADP] = higher rate of O2 uptake

- High [ATP] = lower rate of O2 uptake

Question 17

17) Name the 3 inhibitors of oxidative phosphorylation and their action

Answer 17

• CN- and CO inhibit cytochromes

- Rotenone inhibits Coenzyme Q

Question 18

18) Define uncoupling agent

Answer 18

• Provides easier route for H+ to return to matrix, from intermembrane space (bypassing ATP synthase so energy produced is used as heat rather than for phosphorylation)

Question 19

19) Name 2 uncouplers of oxidative phosphorylation.

Answer 19

• Dinitrophenol (DNP)

- Thermogenin protein (present in brown adipose tissue)

Question 20

20) Total ATP yield for 1 molecule of glucose

Answer 20

• 30/32 ATP

Question 21

21) Where are the complexes involved in maintaining the proton gradient of the respiratory chain located in the mitochondria and what are their functions?

Answer 21

• Located in cristae
• Complex I : NADH/ubiquinone reductase - feeds e- from NADH into the respiratory chain, transfers to CoQ
• Complex III : cytochrome C reductase - accepts e- from CoQ and transfers them to small, soluble e- carrier protein cytochrome c
• Complex IV : cytochrome C oxidase - transfers e- from cytochrome c to molecular oxygen

Question 22

22) Which complex is not involved in maintaining the proton gradient and what is its function?

Answer 22

• Complex II : succinate dehydrogenase -transfers e- from succinate directly to CoQ and does not contribute to proton gradient