Electron transport chain and oxidative phosphorylation - Part 2

Question 1

What are the two sides of NADH DH called?

Answer 1

N - inside - matrix

P - peripheral - outside

Question 2

What is the active site for NADH on complex 1?

Answer 2

Matrix arm

Question 3

Where is the binding site for coq10 on NADH DH?

Answer 3

In the membrane

Question 4

Transfer from NADH to FMN in NADH DH is done as what?

Answer 4

Hydride ion

Question 5

Can coq10 in NADH DH only take one electron?

Answer 5

No, takes one electron from Fe-S center and then waits for the other, allowing it to leave.

Question 6

How does Coq10 (reduced) get to complex 3?

Answer 6

Simple diffusion following a concentration gradient

Question 7

What does electron transfer from NADH to coq10 do to complex 1?

Answer 7

Causes a conformational change which leads to pumping out of 4 protons.

Question 8

In complex 2, succinate DH transfer electrons from ______ to ____ which then transfers to ____.

Answer 8

succinate –> FAD –> coq10

Question 9

FAD becomes FADH2 during the ______ DH reaction in the CAC.

Answer 9

succinate

Question 10

What other DH is present at the same site as complex 2 leading to electron transfer to coq10?

Answer 10

FA-CoA DH

Question 11

What are the three ways that electrons are transferred from FADH2 to coq10?

Answer 11

1 - FA
2 - Succinate DH
3 - Glycerol-3-phosphate DH

Question 12

Complex 2 has three parts, these are?

Answer 12

1 - Succinate DH
2 - ETF:Q oxidoreductase
3 - G3P DH

Question 13

In complex 3, what occurs to Coq10?

Answer 13

Reduced and oxidized

Question 14

Describe the Q cycle.

Answer 14

QH2 (ubiquinol) comes to complex 3.
Gives away two electrons in the form of electron-proton pair and protons pumped out.
The acceptors are both ferric ions (Fe3+) and can only accept one electron at a time.
The leftover protons become orphans and are pumped out of the mt membrane.
One electron acceptor is Fe-S, the other is cytochrome bl.
Iron-sulfur center then transfers to cytochrome c1, then to cytochrome C which then gets fully reduced, leaves for complex 4 and gets replaced.

From cytochrome bl, transferred to cytochrome bh, then back to oxidized coq10 - semiubiquinone now.

Semiubiquinone stays there. Meanwhile, another QH2 arrives and performs the same cycle.
Partially reduced coq10 receives another electron, fully reduced but, needs protons, finds a proton pair from inside the matrix and takes them. the cycle continues and two protons are pumped out.
Total of 4 H+ pumped out.

Question 15

In complex 4, also called _______ _ ______, there are three subunits.
What does each one contain?

Answer 15

Cytochrome c oxidase

Subunit 1: contains two heme groups (a and a3) and a Cu ion (CuB)

Subunit 2: CuA and Cyt c binding site

Subunit 3: role not understood but essential for function

Question 16

Where is the binding site for cyt C on complex 4?

Answer 16

unit 2

Question 17

Copper and iron centers can accept how many electrons, respectively?

Answer 17

1 each

Question 18

For an oxygen molecule to be reduced, how many electrons does it need?

Answer 18

4

Question 19

What is unit 3 required for in complex 4?

What happens if it’s defective?

Answer 19

Holding oxygen in place, doesn’t release it until fully reduced.

Can get superoxide radical.

Question 20

If starting with NADH, how many oxygen atoms will be reduced?
Molecules?

Answer 20

1

1/2

Question 21

From one NADH, if only two electrons, how many protons pumped out?

Answer 21

2

Question 22

How many molecules of oxygen get reduced by FADH2?

atoms?

Answer 22

1/2

1

Question 23

What is the chemical coupling hypothesis?

What are its problems?

Answer 23

Oxidation coupled to ATP synthesis.
Energy is conserved through the formation of a high energy intermediate (similar to 1,3-BPG) which can be used to generate ATP.

Problems:
1 - No high energy intermediate detected
2 - Breaking the mt membrane blocks ATP synthesis

Question 24

What is the conformational-coupling hypothesis?

What were the problems with this hypothesis?

Answer 24

Electron transport oxidation energy conserved in the form of conformational energy which can be used to synthesize ATP.

Problems:
1 - No evidence for ET proteins making ATP
2 - Breaking the inner mt membrane blocks ATP synthesis

Question 25

What were Mitchell’s observations for the chemi-osmotic hypothesis?

Answer 25

1 - intact mt membrane required for oxidative phosphorylation
2 - inner mt membrane impermeable to H+, K+, OH- and Cl-
3 - ET –> results in transport of H+ out of mt –> electrochemical gradient
4 - Compounds that increase permeability to mt membrane dissipate the electrochemical gradient
(allow electron transport but inhibit ATP synthesis)

Question 26

What was the chemiosmotic hypothesis?

Answer 26

Oxidation and electron transport generates an electrochemical gradient across the mt membrane through proton transport whose energy can be used to synthesize ATP.

Question 27

What were the two proposed mechanism of H+ transport?

Answer 27

Redox loop mechanism

Proton pump mechanism

Question 28

What was the redox loop mechanism?

Answer 28

Similar to Q-cycle
In each complex where oxidation occurs, carrier picks up protons from the matrix and, during the process of transfer, release the protons to the outside.

Only sufficient for 2 protons being pumped.

Question 29

What was the proton pump mechanism. What was its support?

Answer 29

During redox rxn in ETC components, reduction causes conformational change which decreases the pKa of the side chain, exposing it to the outside thereby dissociating protons.
Reoxidation restores the original conformation.

Its support came from the proton pump in bacterial rhodopsin.
Light driven conformational change which led to release of protons outside

Question 30

What were mitchell’s experiments that led to him winning the Nobel prize?

Answer 30

1 - Coupling of ET to ATP synthesis - any inhibitor of ETC complexes also inhibits ATP synthesis

2 - Experiments to show uncoupling of ETC to ATP synthesis

Question 31

What were the two things monitored in Mitchell’s experiments?

Answer 31

Oxygen consumption and ATP synthesis.

Question 32

Draw the graphs showing Mitchell’s experiments, coupling and uncoupling.
Explain each point as well.

Answer 32

Refer to notes.