B L2

Question 1

Describe the structure of the mitochondria. Permeability of its membranes. Contents.

Answer 1

Question 2

Where do glycolysis, TCA cycle and the ETC occur?

Answer 2

Glycolysis –> Cytoplasm of mitochondria
TCA –> matrix of mito.
ETC –> inner membrane of mito.

Question 3

What are the requirements for the membrane for ETC/ chemiosmotic energy coupling ?

Answer 3

The proton gradient needed for ATP synthesis can be stably established across a membrane that is impermeable to ions.
– plasma membrane in bacteria
– inner membrane in mitochondria
– thylakoid membrane in chloroplasts
* The membrane must contain proteins that couple the “downhill” flow of electrons in the electron-transfer chain with the “uphill” flow of protons across the membrane.
* The membrane must contain a protein that couples the “downhill” flow of protons to the phosphorylation of ADP.

Question 4

What are the main reduced fuels for the cell?

Answer 4

Carbs, lipids, amino acids

Question 5

Which membrane proteins pump protons in the ETC? What is the proton gradient set up by them? What is the chemical and electric potential established as a result of this proton gradient?

Answer 5

• Complex I, III and IV
• Protons pumped from matrix into intermembrane space thus higher conc. of protons in the intermemb space than in matrix
• Chemical: high conc of protons in intermemb. space thus lower pH (acidic) and higher pH (alkaline) in matrix
• Electrical: high conc of protons in intermemb. space thus more +ve charge than in matrix.

Question 6

How many electrons can a cytochrome carry?
Which protein complexes do they move between?

Answer 6

• one electron carrier
• Move btwn protein complex III and IV

Question 7

What drives ATP synthesis in the ETC?

Answer 7

The proton motive force set up by the proton gradient establishes a chemical and electric potential.
This electrochemical potential causes the ATP synthase (complex V) to drive production of ATP.

Question 8

How many electrons can a Fe-S cluster carry?
Which protein complexes are they present in? Where does the sulfur come from?

Answer 8

one electron carrier
- Present in complex I, II and III
- Cysteine residues

Question 9

How many sulfur atoms will be present in an Fe-S cluster in relation to the iron atoms?

Answer 9

They will be equal in number
same number of Fe as S atoms

Question 10

What type of macromolecule is ubiquinone?

Answer 10

It is a lipid
NOT A PROTEIN!!

Question 11

What is the reduced form of ubiquinone? How many electrons and protons does it accept/carry?

Answer 11

Ubiquinol
When ubiquinone accepts 2 electrons and 2 protons it changes into ubiquinol – which is an alcohol and can freely diffuse in the membrane allowing it to transport electrons

Question 12

What is ubiquinol also known as? What is its function? Which protein complexes is it linked to in the ETC?

Answer 12

Coenzyme Q
Ubiquinone is reduced to form coenzyme Q (gains 2 e- and 2 H+)
It thus transports electrons from complexes I, II and III (From III to IV it’s cytochrome c)

Question 13

What is the name of complex I? Which cofactor binds to it?

Answer 13

NADH ubiquinone oxidoreductase
NADH binds to this protein complex at its binding site on the matrix side and gets oxidised – thus gives up 2 e-

Question 14

Which prosthetic group accepts the electrons from NADH that binds to complex I? How many electrons?

Answer 14

NADH gets oxidised and gives up 2 e- which are accepted by the prosthetic group – FMN (Flavin mononucleotide)

Question 15

Briefly explain what happens at Complex I (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)

Question 16

What is the name of Complex II? What does it accept its electrons from? How many electrons?

Answer 16

Succinate dehydrogenase
It accepts its electrons from FADH2 (succinate - a product of TCA cycle - passes on 2 e- to FAD which becomes FADH2 - FADH2 then gives the e- that travel along Fe-S clusters)
It accepts 2 electrons from FADH2

Question 17

How many protons does complex II pump?

Answer 17

None - it is not involved in the pumping of protons

Question 18

What are the 2 roles of complex II?

Answer 18

• Converts succinate to fumarate
• Captures and donates e- in the ETC.

Question 19

What is the final acceptor of electrons in complex II?

Answer 19

Coenzyme Q (ubiquinol –> ubiquinone becomes ubiquinol on accepting electrons)

Question 20

Briefly explain what happens at Complex II (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)

Question 21

What is the name of complex III? What does it accept its electrons from? how many?

Answer 21

Cytochrome c oxidoreductase
From coenzyme Q (QH2)
It uses 2 electrons from from QH2 to reduce cytochrome c (so it can act as an electron carrier)

Question 22

What is the final acceptor of electrons in complex III? How many electrons does it carry?

Answer 22

Cytochrome c
It carries 1 electron

Question 23

How are cytochrome c and coenzyme Q different in their movement and electron carrying capacity?

Answer 23

Cytochrome c –
> Moves through the intermembrane space
> Carries one electron
> Its a protein

Coenzyme Q (QH2) –
> moves through the inner membrane itself
> carries 2 electrons
> Its a lipid

Question 24

Briefly explain what happens at Complex III (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)

Question 25

Name the complex IV? What does it accept its electrons from?

Answer 25

Cytochrome oxidase
It accepts its electrons from cytochrome c

Question 26

Briefly explain what happens at Complex IV (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)

Question 27

Is NADH or FADH2 more effective in ATP synthesis? why?

Answer 27

NADH
as NADH pumps a net charge of 11 protons into IMS
while FADH2 only creates a net charge difference of 6 protons

Question 28

What are the 3 ways in which a electrochemical proton gradient can be established by the ETC?

Answer 28

• Actively transporting protons across the membrane (by complex I, III and IV)
• Chemically removing protons from the matrix ( by reduction of CoQ and Oxygen)
• Releasing protons into the IMS (By oxidation of QH2)

Question 29

What drives ATP synthesis

Answer 29

The electrochemical proton motive force that is set up by the proton gradient thru the pumping action of the protein complexes in the ETC.

Question 30

What is complex V also called

Answer 30

ATP synthase

Question 31

Describe how ATP synthase generates ATP

Answer 31

As each proton moves/translocates thru the complex, the F0 subunit rotates
This causes a conformational change in the F1 subunit in the mitochondrial matrix
Energy generated by this rotation results in ATP synthesis

Question 32

What is the ATP yield of glycolysis and complete oxidation of glucose

Answer 32

Glycolysis –>
2 ATP

Total oxidation –>
30 or 32

Question 33

What do the following inhibit:
- Rotenone –>
- Oligomyocin –>
- Cyanide, CO –>
- DNP –>

Answer 33

• Rotenone –> Complex 1
• Oligomyocin –> Complex V
• Cyanide, CO –> Complex IV
• DNP –> inhibitor of proton migration

Question 34

What is the use of UCP-1?

Answer 34

Uncoupling protein - 1
In babies and in hibernating animals
It is possible to uncouple ATP synthesis from the ETC to generate heat
The proton gradient established by the ETC is used to generate heat instead of for ATP synthesis.