Power conversion in Mitochondria L6-7

Question 1

What are the two Flavin molecules in the ETC?

Answer 1

FMN and FAD

Question 2

What do cytochromes contain?

Answer 2

Haem prosthetic groups(include iron)
undergo 1 electron reduction with polyphyrin Fe3+–>Fe2+
Em depends on structure of haem and local environment of the protein
Type A-extra formyl group and C15 hydrocarbon tail
Type B-Like haem in haemoglobin
Type C-Covalently attached to cysteines

Question 3

How far can electrons jump?

Answer 3

about 15Å=10^4s^-1

This is sufficient for respiration

Question 4

Which amino acids have the ability to accept H+ ions?

Answer 4

Glu, Asp, His, Lys, Arg (acid and bases)

They can’t accept electrons though cos that damages them

Question 5

What is complex I? And what cofactors does it have?

Answer 5

NADH dehydrogenase or NADH-Q-Oxidoreductase.
It has a peripheral hydrophilic domain and membrane domain
FMN (accepts 2e-) and 9 Fe-S clusters only 7 used in ETC
2Fe-S=2Fe-2S
7Fe-S=4Fe-4S
NB/ 4H+ pumper per 2e-

Question 6

In the hydrophilic/hydrophobic domain what are the protein subunits called? Complex I

Answer 6

hydrophilic=Nqo (NADH-Q-Oxidoreductase.)

hydrophobic=Nuo (NADH ubiquinone oxidoreductase)

Question 7

Interesting fact about hydrophobic membrane domain of Complex I

Answer 7

NuoL,M,N are all homologous to the H+/Na+ antiporter, Therefore they presumably must have an H+ channel

Question 8

What is noteworthy of NuoL,M,N in the hydrophobic membrane domain of Complex I?

Answer 8

They all have 2 broken helices
TM7 and TM12 are broken and each have a conserved residue (Lys or Glu) at helix break (3 channels have a conserved residue)
Can accept H+ to form a proton channel

Question 9

What is the difference between NuoL,M,N ?

Answer 9

NuoL protein has extra 2 TM helices compared to NuoM,N

These are linked by a long amphipathic helix, HL lying along the membrane surface

Question 10

How are protons pumped in complex I?

Answer 10

Structure suggests an indirect mechanism, since redox centres are too far from the membrane domain.
Conf change in hydrophilic domain is transmitted through HL amphipathic helix. HL acts as a piston coordinating a TILT of the 3 broken helices (NuoL,M,N) resulting in proton pumping

Question 11

How many protons are pumped through complex I?

Answer 11

4
Transport of protons against its gradient is given by energy from the conf change as electrons pass from high to low midpoint potentials

Question 12

What is complex II known as in the ETC?

Answer 12

Succinate dehydrogenase/succinate:ubiquinone oxidoreductase/fumarate reductase
enzyme of the citric acid cycle/the only memb bound enzyme of the citric acid cycle
Succinate—>fumarate

Question 13

What are the co-factors in complex II?

Answer 13

FAD, 3FeS centres, b-type heam

Question 14

Are there any H+ involved with complex II?

Answer 14

Yes, although there is no net transfer of protons, taken and delivered on same side-contributes to hydrophobic quinone pool
The H+/energy released from reduced fumarate is relayed to reduced quinone

Question 15

What is complex III known as?

Answer 15

bc1 complex/cytochrome bc1/ubiquinol:cytochrome c oxidoreductase
This complex is a DIMER
This is where the Q cycle takes place

Question 16

What are the three subunits of complex III?

Answer 16

Rieske protein (2Fe-2S) -peripheral
Cytochrome b (bL bH)
Cytochrome c1 -peripheral
peripheral subunits do not effect enzyme activity
Redox carriers are immobilised onto the protein scaffold.
QP(UQ binding site at P-side)
QN(UQ binding site at N side)

Question 17

How many protons are translocated through complex III?

Answer 17

4
2H+ are picked up from matrix
4H+ are released from 2 x QH2 (come from NADH/Succinate dehydrogenase)
Net effect = 2H+ translocated across the membrane

Question 18

Why are there 2 Q binding sites?

Answer 18

Q and QH2 are uncharged-can freely diffuse within the membrane
Qradical- is negatively charged, unfavourable movement to N side yet it must be reduced close to N side to pick up a H+ from the matrix. The unfavourable movement creates high energy (repulsive effect) which means it can quickly pick up a proton and deliver it to the other side of the memb.
Uses high electronic potentials to directly translocate H+

Question 19

Why are there 2 b haems?

Answer 19

electron movement from bL to bH is unfavourable as moves to the negative side. This is offset by very favourable change in Em from -100mV (bL) to +50mv(bH)
difference =150mV
A highly negative midpoint potential will drive an electron to move irrespective of it being a disfavour able reaction.

Question 20

Is cytochrome c soluble?

Answer 20

Yes it is water-soluble and peripherally associated with the P side of the IMS of mitochondrial membrane. Contains a c type heam (Fe3+—>Fe2+)

Question 21

What is complex IV called and what does it reduce?

Answer 21

Cytochrome c oxidase. Reduces oxygen to water.

This is also a DIMER (Complex III is also a dimer)

Question 22

What redox centres does complex IV have?

Answer 22

CuA consists of 2 Cu atoms, coordinated by cis and his side chains (where electrons come in)
Haem a
Haem a3 can also bind oxygen in reduced Fe2+ (like haemoglobin)
CuB
It also has important tyrosine residue that becomes oxidised and reduced by a proton form the matrix?

Question 23

How many protons does complex IV translocate?

Answer 23

2 per 2e- to make (1/2 O2)

Question 24

What is the net effect of protons in the mitochondrial ETC?

Answer 24

Passing 2e-s from NADH to 1/2 O2

10H+ pumped