Stage 3 - electron transfer and oxidative phosphorylation

Question 1

Where does electron transfer and oxidative phosphorylation take place?

Answer 1

Mitochondria

Question 2

What is released from the oxidation of NADH/FADH2 and is used to synthesize ATP by ETC

Answer 2

energy

Question 3

What does O2 provide? positive and negative?

Answer 3

an energy source but also uncontrolled oxidation

Question 4

The oxidation of reduced cofactors produce a large and negative delta G. Why?

Answer 4

bcs O2 is a good oxidizing agent

Question 5

Why is NADH delta G more negative than FADH2?

Answer 5

bcs its a stronger reducing agent

Question 6

Reoxidation of NADH and FADH2 is broken into smaller steps using…

Answer 6

reducing equivalents of the reduced cofactors

Question 7

What is the ETC comprised of?

Answer 7

electron carriers in the order of increasing reduction potential - O2 is last (least negative)
and
enzymes which are electron carrier complexes that catalyze the transfer of 1 electron carrier to another

Question 8

Electron carriers - CoQ
What can it accept?
What does it collect?

Answer 8

can accept 1 (transfer of an H atom)(semiquinone) or 2 electrons (transfer of a hydride ion) to form the alcohol ubiquinol
reducing equivalents

Question 9

Electron carriers - Cytochrome C
What does it shuttle? from where to where?
How many electrons does it carry at once?
How does it do this?

Answer 9

family of proteins with an iron heme prosthetic group
shuttles electrons from complex 3 to complex 4 of ETC
1 electron
direct transfer as reduction Fe3+ to Fe2+

Question 10

Complex 1 enzyme
what does it do?

Answer 10

NADH dehydrogenase
transfer electrons to Q causing Q to reduce to QH2

Question 11

Complex2 enzyme
Why does it enter chain later?
What does it NOT do?

Answer 11

succinate dehydrogenase
enters chain later because weaker reducing agent than NADH
pump protons to IMS

Question 12

Complex 3 enzyme
what does it do?

Answer 12

cytochrome C reductase
QH2 passes electrons to cytochrome C

Question 13

Complex 4 enzyme
what does it do

Answer 13

cytochrome oxidase
transfers electrons from reduced cytochrome C to Q2

Question 14

What is the electron flow through complex 1, 2 and 4 accompanied by?

Answer 14

proton flow from matrix to IMS

Question 15

Electron transport chain summary

Answer 15

NADH->Q->cytochrome C->O2 (FADH2 enters at Q)

Question 16

If an inhibitor is placed anywhere on the chain before it gets ______ and after it gets ______

Answer 16

reduced, oxidized

Question 17

Complex 1 inhibitors

Answer 17

rotenone barbiturates

Question 18

complex 3 inhibitors

Answer 18

animycin A

Question 19

complex 4 inhibitors

Answer 19

carbon dioxide, cyanide

Question 20

What is the proton gradient?

Answer 20

energy available through oxidation of NADH/FADH2 throughout the ETC

Question 21

How many protons does complex 1, 2 and 4 produce?

Answer 21

4,4,2

Question 22

If one FADH2 is oxidized how many protons are made?

Answer 22

6

Question 23

What kind of energy is the proton motive force made of?

Answer 23

1. Chemical potential energy - difference in [H+]
2. Electrical potential energy - separation of charges

Question 24

What does chemiosmotic theory explain?

Answer 24

obligatory coupling seen between electron transfer and ATP synthesis

Question 25

What is chemiosmotic theory? Free ___ from ____ reactions is used by the ETC to pump _____ moving H+ from the _____ to the ___. Energy is stored as ______ _______. The energy of the electrochemical gradient is released and used for ______ of _____ _____ by the ATP enzyme.

Answer 25

energy, redox, protons, matrix, IMS electrochemical gradient generation, ATP synthase

Question 26

What does inhibition of electron transfer do?

Answer 26

stops ATP synthesis and O2 consumption

Question 27

What does inhibition of ATP synthase do

Answer 27

stops ETC because energy required to pump protons across this gradient will eventually exceed the available energy from NADH oxidation no pump protons = no ETC

Question 28

What happens when the reactions are uncoupled?

Answer 28

IMM is disrupted, therefore protein gradient eliminated (no energy to synthesis ATP from ATP synthase enzyme). Electron transport continues but ATP synthesis stops.

Question 29

Example of an uncoupler Dinitrophenol. Explain what it does.

Answer 29

DNP turns negative and crosses back into IMM delocalizing the aromatic ring therefore collapsing the protein gradient and stopping synthesis of ATP.

Question 30

What happens to the energy from the proton gradient in the presence of an uncoupler?

Answer 30

energy from proton gradient is not consumed by ATP formation but dissipated as heat.

Question 31

What does the proton motive force do?

Answer 31

Release ATP from the enzyme

Question 32

Cyanide (CN-) is an inhibitor of the electron transport chain (ETC). However, the addition of CN- to the mitochondria not only inhibits the ETC but also inhibits ATP synthesis. Explain the reason for this.

Answer 32

Cyanide inhibits complex 4 of ETC which also inhibits ATP synthesis because electrons can no longer be pumped into intermembrane space.