L32 Mitochondrial Electron Transport Chain

Question 1

What is the METC

Answer 1

final common pathway in aerobic cells by which electrons derived from various compounds are transferred to O2 to form H20

Question 2

How does energy production occur in ETC

Answer 2

1-electron transport between diff complexes (oxidation)
2-proton pumping in to inter membrane space
3-synthesis of ATP from ADP and Pi(phosphorylation)

Question 3

Describe Complex I

Answer 3

Ubiquinone oxidoreductase
Formed of:
.many polypeptides
.FMN co enzyme
.7 FeS centers
.Es are transferred from NADH to FMN to diff FeS Centers then UQ to be reduced to UQH2

4 protons pumped

Question 4

Describe complex II

Answer 4

Succinate: ubiquinone oxidoreductase
Formed of:
Succinate dehydrogenase 
FAD coenzyme
Two FeS centers
Catalyzes transfer of e’s from FADH2(released by oxidation of succinate) to UQ To form UQH2 

No protons pumped

Question 5

Describe complex III

Answer 5

Ubiquinone:(ferri cytochrome C oxidoreductase)
Formed of
ONE FeS center
Cytochrome b
Cytochrome c1
Transfers electrons from UQH2 to cytochrome C

3 protons pumped

Question 6

Describe Complex IV

Answer 6

Ferro cytochromeC: oxygen oxidoreductase

Two cytochromes (a and a3)
Two atoms of Cu

Transfers two e’s from cytochrome C to oxygen which combines with 2 H+ to form h2O

4 protons pumped

Question 7

What do cytochromes contain

Answer 7

Heme group made of a porphyrin ring containing and atom of iron
Iron atom is reversibly converted from Fe 2+to Fe3+

Question 8

Describe cytochrome and its function

Answer 8

Mobile element of ETC
in inter membrane space loosely associated with outer face of inner membrane
Electrons passed along the chain from cytochrome bc1(complex III) to cytochrome c and then cytochrome a+a3(complex IV)

Question 9

How are electrons insured to flow from beginning to end of ETC

Answer 9

Components of ETC are arranged according to their oxidation reduction potential

Question 10

What are the coupling sites at which proton pumping occurs

Answer 10

Coupling site I: in between FMN(in complex I) and CO Q
Coupling site II: between cytochrome b and c1 (in complex III)
Coupling site III: at cytochrome a and a3 (in complex IV)

Question 11

Describe ubiquinone and its function

Answer 11

Made from an intermediate of cholesterol synthesis

Links flavoprotein dehydrogenases to cytochromes

Question 12

Whats a drawback of the ETC

Answer 12

Potential leakage of electrons outside of mitochondria and formation of reactive oxygen species which have deleterious effects on all body molecules and can cause cancer

Question 13

How many protons does one ATP molecule need to be formed

Answer 13

4 protons

Question 14

How is respiratory chain controlled

Answer 14

By inhibitors
A) inhibitors of respiratory chain proper
B) inhibitors of oxidative phosphorylation
C) uncouplers of oxidative phosphorylation

Question 15

Explain how inhibitors of respiratory chain proper work

Answer 15

Inhibit ETC and thus proton pumping examples:
Barbiturates:sleeping medicine 
Piercidin A: antibiotic 
Rotenone: rat poison 
Antimycin :anti fungal
Hydrogen sulfide gas
carbon monoxide 
Cyanide (poison)

Question 16

Explain how inhibitors of oxidative phosphorylation work

Answer 16

Inhibit transport of ADP in to and ATP out of mitochondria
Ex: oligomycin (antibiotic)
Atractyloside (poison in some plants)

Question 17

Explain how uncouplers of oxidative phosphorylation work

Answer 17

Dissociate oxidation in respiratory chain from phosphorylation
ETC continues but pumped H+ goes back in through channels other than ATP synthase
Ex: thyroxine, Ca2+,large doses of aspirin and uncoupling protein

Question 18

What tissues are most affected by defects in oxidative phosphorylation

Answer 18

Central  nervous system
Heart muscle
Skeletal 
Liver 
Diseases usually accompanied by vision loss and mental retardation