Regulation of Oxidative Phosphorylation

Question 1

Coenzyme Q

Answer 1

Membrane bound but mobile electron carrier from complex I/II to III
3 stages of redox:
1) ubiquinone (oxidized): Q
2) semiquinone radical (partially reduced): QH
3) ubiquinol (fully reduced): QH2

Question 2

Iron-sulfur proteins

Answer 2

Type A: Fe with 4 S in X shape
Type B: 2 Fe with 6 S in lattice
Type C: 4 Fe with S in cube shape

Question 3

Cytochrome structure

Answer 3

Contains central heme group with Fe
Types A, B and C (type c present in mitochondrial membrane)

Question 4

Complex I pathway
electron/proton supply sources

Answer 4

1) NADH + H+ transfer 2e –> FMN
2) FMN transfers 2e –> Fe-S protein
3) Fe-S protein transfer 2e –> Q (oxidized) –> QH2 (reduced)
QH2 can move to complex III

NADH supplied by: beta oxidation, glycolysis, pyruvate oxidation, TCA and AA oxidation
H+ supplied by mitochondrial matrix

Question 5

FMN and FAD

Answer 5

Flavin mononucleotide
Flavin adenosine dinucleotide

Question 6

Complex II pathway
Electron/proton supply sources

Answer 6

Is also succinate dehydrogenase from TCA cycle
1) FAD transfers 2e –> Fe-S protein
2) Fe-S protein transfer 2e –> Q (oxidized) –> QH2 (reduced)
QH2 can move to complex III
or
1) Acyl-coA dehydrogenase (step 1 beta ox pathway) produces FADH2, FADH2 transfers 2e –> ETF
2) ETF (e transferring flavoprotein) –> Q oxidoreductase enzyme
3) Q oxidoreductase enzyme transfers 2e –> Q –> QH2

FAD sources: TCA (succinate dehydrogenase), beta oxidation (acyl-coA dehydrogenase), glycerol-3-phosphate shuttle (inter-membrane space side, from glycerol catabolism)

Question 7

Complex I size

Answer 7

Largest of the 4 subunits, 45 subunits encoded by nuclear and mitochondrial genes

Question 8

Complex I equation

Answer 8

NADH + Q + 5H+(n) –> QH2 + 4H+(p) + NAD+

Question 9

Complex II subunits

Answer 9

Subunit A: contains FAD and succinate binding site

Subunit B: contains 2 Fe-S centers

Subunit C: spans membrane, contains 1 Fe-S center, heme b, ubiquinone binding and 1 phosphatidylethanolamine

Subunit D: contains 1 phosphatidylethanolamine

Question 10

Complex III net equation

Answer 10

QH2 + 2 cytochrome C (ox) + 2H+(n) –> Q + 2 cytochrome c (red) + 4H+(p)

Question 11

cytochrome b

Answer 11

embedded in complex III, 2 units

Question 12

Complex III Stage 1 and 2 pathway and equations

Answer 12

QH2 + Q + cytochrome c (ox) –> Q + QH + 2H+(p) + cytochrome c (red):
1) QH2 donates 1e to Q –> QH (radical)
2) QH2 donates other 1e to Fe-S proteins
3) Fe-S proteins transfer 1e –> heme c1 on cytochrome c (ox) –> cytochrome c (red)
Cytochrome c can travel to complex IV

QH2 + QH + 2H+(n) + cytochrome c (ox) –> Q + 2H+(p) + QH2 + cytochrome c (red)
4) New QH2 donates 1e to QH –> QH2
5) New QH2 also donates 1e to Fe-S then cytochrome C heme (ox)
6) Cytochrome C (ox) –> cytochrome c (red)
Can travel to complex IV

Question 13

Complex IV in bacteria

Answer 13

cytochrome oxidase
large complex dimer with 3 subunits in bacteria
Subunit I: contains Fe-Cu center (2 heme and 1 Cu)
Subunit II: 2 Cu
Subunit III: responsible for H+ movement through subunit II

Question 14

Complex IV pathway

Answer 14

1) cytochrome c (postive side) donates 1e –> Cu (subunit II)
2) Cu passes 1e –> Fe-Cu center (subunit I)
3) Steps 1/2 repeat 4x, 4e are donated to O2
4) 2H+ combined with O2 to form H2O
5) 2H+ are pumped through to positive side
4 H+ removed (4 cytochrome c), 2H+ (pos), 2H+ bound H2O

Question 15

Complex I-IV equation
Complex II-IV equation

Answer 15

NADH + 11H+(n) + 1/2O2 –> NAD+ + 10H+(p) + H2O
FADH2 + 6H+(n) + 1/2O2 –> FAD + 6H+(p) + H2O

Question 16

How the electrochemical proton gradient is formed

Answer 16

Active transport of H+: Complex I and IV
Release of H+: Complex III (oxidation of QH2)
Reduction of Q: Complexes I, II, III
Reduction of oxygen: complex IV

Question 17

Malate-aspartate shuttle

Answer 17

NADH from glycolysis cannot cross inner mitochondrial membrane
1) NADH used to convert oxaloacetate –> malate (intermembrane space)
2) Malate crosses via a-ketoglutarate malate transporter
3) Malate reconverted to oxaloacetate and NADH + H+
4) Oxaloacetate converted to aspartate (converting glutamate –>a-ket-glut at same time like in urea cycle)
5) Aspartate and a-ket-glut transport back (separately), aspartate-glutamate transporter

Net effect: movement of NADH from intermembrane space to mitochondrial matrix for oxidative phosphorylation

Question 18

NADH shuttle in skeletal muscle and brain

Answer 18

to get around mitochondrial inner membrane impermeability
1) glycerol-3-phosphate shuttle converts dihydroxyacetone phosphate –> glycerol-3-phosphate
2) G-3-P dehydrogenase converts glycerol-3-phosphate back to dihydroxyacetone phosphate and in the process converts FAD –> FADH2
FADH2 can then reduce Q –> QH2 (complex II, intermembrane space side)

Question 19

ATP yield from complete oxidation of glucose

Answer 19

30-32 ATP

Question 20

Beta oxidation NADH/FADH2 and ATP yields by enzyme for 1 palmitate

Answer 20

Acyl-coA dehydrogenase: 7 FADH2 –> 10.5 ATP
B-hydroxyacyl-coA dehydrogenase: 7 NADH –> 17.5 ATP

Question 21

Isocitrate, a-ket-glut dehydrogenases and malate dehydrogenase yield for 1 palmitate

Answer 21

8 NADH –> 20 ATP

Question 22

Succinyl-coA dehydrogenase yields for 1 palmitate
Succinate dehydrogenase yields

Answer 22

8 ATP from GTP
8 FADH2 –> 12 ATP

Question 23

1 palmitate total yield

Answer 23

108 ATP

Question 24

Regulation of oxidative phosphorylation

Answer 24

based on ATP/ADP-Pi concentration ratios
ATP is synthesized as fast as it is utilized