Oxidative Phosphorylation

Question 1

Overview of cellular respiration

Answer 1

Electrons from NADH and FADH2 are transferred to oxygen along the ETC (respiratory chain);
Energy released is large enough to pump protons across IMM to create a proton gradient;
Protons flow back and generate ATP (ATP synthase complex). ;
Tightly coupled;

Question 2

Electron transport chain

Answer 2

IMM;
4 protein complexes (Complex I to IV)
3 proton pumps (complex I, II, IV)
1 link to tea cycle (complex II);
2 small components (CoQ, cytochrome c);

Question 3

Complex I

Answer 3

NADH dehydrogenase;
34 polypeptides;
NADH binds to complex I;
Accepts electrons from NADH;
Transfers electrons to CoQ (via FMN and Fe-S);
4H+ pumped out;

Question 4

Complex II

Answer 4

Succinate dehydrogenase (TCA cycle);
Enzyme of TCA cycle (succinate to fumarate);
Accept electrons from FADH2;
Transfers electrons to CoQ by FMN or Fe-S;

Question 5

Coenzyme Q (CoQ)

Answer 5

Small lipid soluble compound - hydrophobic;
Diffuses rapidly with IMM - mobile carrier;
Accepts electrons from Fe-S proteins from complex I and II;
Transfers electrons to Complex III/ Cytochrome C (Q cycle);

Question 6

Complex III

Answer 6

Heme prosthetic group;
Accepts electrons from CoQ;
Transfers them to cytochrome C;
Two protons pumped across IMM;

Question 7

Cytochrome C

Answer 7

Peripheral membrane protein;
Binds to complex II and transfers electrons to complex IV;
Highly conserved;

Question 8

Complex IV

Answer 8

13 protein subunits containing 2 heme groups and 3 copper ions;
Accept electrons from cytochrome c;
Transfers them to 1/2 O2 which is reduced to form H2O;
8 protons pumped across IMM;

Question 9

Why are electrons transferred?

Answer 9

Accepting carrier has a higher affinity for electrons than the donating carrier (redox potential)

Question 10

ATP synthase (complex V)

Answer 10

IMM;
Composed of 2 sub units:
F1 ATPase - generates ATP;
F0 Coupling factor - protein channel spanning IMM;

Protons pass through channel which causes conformational change in F1 causing ATP to be synthesized from ADP and Pi;

Question 11

ATP synthase working details

Answer 11

As protons pumped from cytosolic side to matrix through F0 proton channel, they drive the rotation of the C ring of F0 which causes conformational change in beta subunit of F1 which bind ADP and Pi to form ATP;

Question 12

ATP yield

Answer 12

NADH - 3 ATP (2.5);
FADH2 - 2 ATP (1.5);
For TCA cycle - 12 ATP;
For 1 molecule of ATP - 38;

Question 13

P/O ratios

Answer 13

Number of ATP molecules formed per oxygen
NADH ratio - 3;
FADH2 - 2;

Question 14

Agents affecting oxidative phosphorylation

Answer 14

ATPase inhibitors - oligomycin;
Site specific inhibitors of ETC;
Uncouplers - neutralise the proton gradient and prevent ATP synthesis;

Question 15

Uncouplers of ETC

Answer 15

Chemicals and natural uncoupling proteins

Question 16

UCP1

Answer 16

Thermogenin;
Mitochondria of brown adipose tissue;
Energy from ET used to generate heat - non shivering thermogenesis;
NB in new borns and hibernating animals;