Mod 9 Flashcards
The electron transport chain
NADH and FADH2 donate their e- to the ETC
Made of five protein complexes embedded within the inner mitochondrial membrane
2 roles of complexes I-IV
- Accept e- and shuttle them along
- Pump protons out of the mitochondrial matrix into the intermembrane space
What shuttles e- between protein complexes
Electron carriers coenzyme Q and cytochrome c
Both lipid soluble = good carriers
(need carriers bc they are charged)
Does the reduction potential increase or decrease as you go from complex I-IV
Reduction potential increases
I -> III -> IV -> oxygen
NADH lowest reduction potential = lowest e-affinity
Oxygen highest reduction potential = highest e- affinity
Are the complexes reduced and re-oxidized?
It’s not the complexes themselves that are reversibly reduced and re-oxidized
redox centers inside that do that
4 types of redox centers
- Coenzymes
- Fe-S clusters
- Cytochromes
- Cu
Each protein complex contains a combo of 2+ types of redox centres
Complex I: NADH to ubiquinone (coenzyme Q)
NADH donates e- to ubiquinone in complex I
protons move from matrix to intermembrane space
NADH + Q +5H
–>
NAD+ + QH2 + 4H+
reduced coenzyme Q picks up 2 protons
Complex II: succinate to ubiquinone
succinate dehydrogenase aka complex II
FAD accepts two e- from succinate
e- passed via Fe-S centers to ubiquinone so it reduces to QH2
succinate + FAD
–>
fumarate + FADH2
Complex III: ubiquinone to cytochrome c
uses 2 e- from QH2 to reduce two molecules of cytochrome c
contains Fe-S clusters, cyto b, and cyto c
sends 4 protons out from matrix to intermembrane space
Complex IV: cytochrome c to O2
4 e- used to reduce 1 O2 into two H2Os
uses 4 protons
releases 4 protons
NADH in ETC
NADH donates e- to complex I
Complex I passes to complex III then to complex IV
FADH2 in ETC
FADH2 ⇒ coenzyme in CA cycle that is a prosthetic group covalently bound to the enzyme succinate dehydrogenase which is part of complex II
FADH2 donates e- to complex II
Complex II passes e- to complex III then to complex IV
Coenzyme Q in ETC
aka ubiquinone
Shuttles e- through the membrane to complex III
Cytochrome c in ETC
Shuttles e- from complex III to complex IV
Pumping protons
as e- goes from lower to higher reduction potential, energy is released
uses the energy to drive proton pumping mechanism
Complex I and III → pump 4 protons per e- pair
Complex IV → pump 2 protons per e- pair
Complex II → doesn’t pump protons
Is there a higher concentration of protons inside or outside the membrane? pH? matrix charge?
what do all these relate to?
Higher [protons] outside inner membrane compared to inside of the matrix
Lower pH outside of the inner membrane = more acidic (chemical potential)
Matrix charge is negative (electric potential)
they all relate to an electrochemical gradient
Complex V
aka F1-F0 ATP synthase
Does ATP synthesis aka the oxidative phosphorylation
Composed of a F0 and an F1 subunit
- Held together by a protein ‘stalk’
F0 subunit of complex V
- Proton channel which spans the inner mitochondrial membrane
- Is responsible for allowing protons to enter the matrix
F1 subunit of complex V
- Bulbous portion of the complex on the matrix side of the inner membrane
- Comprises the ATP synthase enzyme responsible for synthesizing ATP
Oxidation of a matrix NADH vs FADH2
NADH pumps 10 protons
FADH2 pumps 6 protons
ATP production from NADH vs FADH2
and P/O ratio
NADH ⇒ yields 3 ATP
P/O ratio: for each mole of oxygen consumed, three high energy phosphate bonds generated per NADH
FADH2 ⇒ yields 2 ATP
P/O ratio: for each mole of oxygen consumed, two high energy phosphate bonds generated FADH2
ATP yield from glucose breakdown
all steps
From oxygen-independent partial oxidation of glucose through substrate level phos through glycolysis ⇒ 2 ATP
Remaining oxidation through pyruvate dehydrogenase reaction and the CA cycle ⇒ 2 GTP = 2 ATP
Glycolysis 2 NADH, pyruvate dehydrogenase 2 NADH, CA cycle 6 NADH and 2 FADH2 ⇒ 34 ATP
Total: 38 ATP
Shuttle for e- from cytosolic NADH
for glycolysis
glycolysis takes place in the cytosol
so issues accessing ETC to donate e- from NADH
2 mechanisms for NADH to donate to donate its e-
1. Glycerol-3-phosphate shuttle
2. Malate-aspartate shuttle
