11.2 Electron Transport Chain Flashcards
Glycolysis occurs in…
the cytosol
Citrate cycle occurs in…
Mitochondrial Matrix
ETS occurs in…
inner mitochondrial membrane
What feeds the ETC?
NADH and FADH2
What are the two routes of electron transport?
- Oxidation of NADH on matrix side of IMM
- Oxidation of FADH2 from either the cytosolic side or the matrix side of IMM
What is the electron flow of NADH?
NADH → Comp I → Q → Comp III → Cyt c → Comp IV → O2
How many protons are pumped across from NADH?
10 H+
What is the electron flow from FADH2?
FADH2→ Comp II → Q → Comp III → cyt c → Comp IV → O2
How many protons are pumped across from FADH2?
6 H+
What facilitates ETC electron flow?
Electron carriers, ordered by increasing E
What does Interruption of e- flow do?
inhibits ATP synthesis
What are some Inhibitors of electron flow?
Rotenone (poison arrows, blocks ETS)
Hydrogen cyanide, CO, antimycin A
Describe in general Complexes I, III, IV
Large multi-subunit complexes translocate protons across IMM
What are the 3 membrane associated FAD/FADH2-containing enzymes?
(3 routes of FADH2 entry)
– Comp II (Succinate dehydrogenase)
– ETF-Q oxidoreductase - lipid metabolism
– Glycerol-3-phosphate dehydrogenase - cytosolic NADH
What is Coenzyme Q?
ubiquinone
-Small hydrophobic e- carrier, diffuses through the membrane
-2 electrons: Comp I/II → Comp III
What is Cytochrome c?
– Small water soluble protein in intermembrane space
– 1 electron: Comp III → Comp IV
Complex I
NADH–ubiquinone oxidoreductase
Complex II
succinate dehydrogenase
Complex III
ubiquinone–cytochrome c oxidoreductase
Complex IV
cytochrome c oxidase
What are Protein-bound redox centers? What are the 3 types?
Bound to proteins in ETC
1. Iron-sulfur or copper centers (1 electron)
2. Hemes (1 electron)
3. Coenzymes FADH2 and FMN (1 or 2 electrons)
What are the 2 Mobile electron carriers?
- Coenzyme Q - small molecule, one or two electrons
- Cytochrome C - small protein, one electron
Describe Complex I
Largest of the 4 complexes (15-40 chains) M
Pumps 4 protons into intermembrane space
Oxidizes NADH
Reduces Q
FMN
Contains 7(+) Fe-S centers
What are the three steps of electron flow of complex I?
- NADH transfers 2 electrons to FMN
- 2 electrons transferred from carrier to carrier
- 2 electrons and 2 protons bind Q forming QH2
(4 protons move from N to P side)
What is the net result of Complex I?
Transfer of 2 e- from NADH to coenzyme Q
4 H+ translocated from matrix to the intermembrane space (P side)
What is the net reaction from complex I?
NADH + Q + 5H+(N) —-> NAD+ + QH2 + 4H+(P)
What are things about Coenzyme Q?
- Mobilee-carrier – Comp I or II —> Comp III
- Entry point for e- pairs into ETS - From CC, fatty acid oxidation, or G3P dehydrogenase
- 1 or 2 electrons – Adapter b/w 2e- to 1e- carriers, Q cycle
Describe Complex II
● Also catalyzes step 6 in citrate cycle
– FAD→FADH2 (1 or 2 electrons)
● 3 Fe-S centers and b-type heme
– 1electron
● Q→QH2
– 1 or 2 electrons
Complex II net result
Oxidizes of FADH2 to FAD
Reduces Q to QH2
No translocation of H+
Complex II net reaction
FADH2 + Q —> FAD + QH2
Describe Complex III
Dimeric complex (11 subunits per monomer)
● Pumps 4 protons into intermembrane space
● 2 Fe-2S centers, 2 b-type & 1 c-type heme – 1electron
● Oxidizes QH2 – 1 or 2 electrons – Q-cycle
● Reduces Cyt C – 1 electron
Complex III net result
Transfer 2e- from QH
Translocation of 4H+ to intermembrane space
Complex III net reaction
QH2 + 2H(N) + 2 Cytochrome C (oxidized) –> Q + 4H+(P) + 2 Cytochrome C (reduced)
What is the Q cycle?
- Occurs in Comp III
- Converts 2 e- transfer to 1 e-
What are the 4 steps of the Q cycle?
- Oxidation of QH2 at Q(P) - electron goes to cytochrome C
- Oxidized Q goes to Q(N)
- New QH2 binds to QP, is oxidized, election goes to a new cytochrome c
- 2nd electron from step 3 reduced semiquinone QN and 2 protons reform QH2
