Electron Transport and ATP Synthesis Flashcards
How electron transport chain works
Reduced coenzymes (NADH, QH2) pass electrons down a reduction potential gradient, ultimately to molecular O2 O2 gains electrons and becomes water
Oxidative phosphorylation
Proton gradient drives ATP synthesis
Mitochondrial inner membrane
Highly folded (cristae) and impermeable to polar/ionic substances Critical membrane for electron transport
Mitochondrial matrix
Contains enzymes for citric acid cycle
Cytosol
Site of glycolysis
Overview of electron transport
- NADH/QH2 (from TCA cycle and fatty acid oxidation) in the matrix pass electrons through many carriers, last to O2
- H+ are pumped to the intermembrane space, creating a charge gradient
- H+ flow is used to drive ATP synthesis by ATP synthase
Chemiosmotic theory
H+ concentration gradient serves as the energy reservoir for ATP synthesis
Uncouplers
Synthetic compounds which disrupt the relationship between oxidation and phosphorylation
Allow O2 to be reduced, but destroy H+ gradient as soon as it’s formed
Complex I of electron transport chain
Transfers 2 electrons from NADH to coenzyme Q
Mechanism of complex I
- 2 electrons are transferred from NADH to FMN (flavin mononucleotide)
- Single electron transfers from FMNH2 to Fe-S cluster
- Single electron transfers from Fe-S cluster to Q, forming QH2
For every 2 electrons that pass through complex I, how many H+ are pumped to intermembrane space?
4 H+ are pumped into intermembrane space
Complex II of electron transport chain
Also called succinate dehydrogenase (complex from step 6 of TCA cycle)
Releases very little free energy and doesn’t directly contribute to H+ gradient
Mechanism of complex II
- 2 electron transfer from succinate to FAD
- Single electron transfers from FADH2 to Fe-S
- Single electron transfers from Fe-S cluster to Q, forming QH2
Complex III of electron transport chain
Also called ubiquinol (QH2): cytochrome c oxidoreductase
Catalyzes transfer of electrons from QH2 to cytochrome c
Mechanism #1 of complex III
- 1 electron transfer from QH2 to cytochrome bL
- Single electron transfers from cytochrome bL to Fe-S cluster
- Single electron transfers from Fe-S cluster to cytochrome c
Mechanism #2 of complex III
- 1 electron transfer from QH to cytochrome bL to cytochrome bH
- Single electron transfers from cytochrome bH to Q (forming 1 QH2)
Each QH2 that passes through complex III results in translocation of how many H+?
4 H+/QH2
Complex IV of electron transport chain
Also called cytochrome c oxidase
Catalyzes transfer of electrons from cytochrome c to O2
Mechanism of complex IV
Single electron transfers until the final transfer to O2
Cytochrome c -> Cu A -> heme a -> heme a3 -> Cu B -> O2
2 components of ATP synthase
F0 component
F1 component
F0 component of ATP synthase
Pore/channel
Embedded in inner mitochondrial membrane
Consists of a and c subunits (protons pass through channel at a/c subunit interface)
F1 component of ATP synthase
Catalytic portion
Anchored to inner membrane (matrix side) by F0
Contains 3 catalytic sites for ATP synthesis
Mechanism of ATP synthase
- A proton travels through F0, causing the c-subunit “rotor” to turn one subunit
- When enough torque has been applied (~3 H+), the gamma subunit “jumps” 120 degrees, causing simultaneous conformational shifts in the active sites (ADP and Pi are joined together to make ATP)
Gamma subunit of F1 component
Portion of F1 component that F1 rotates around (similar to spindle)
Adenine nucleotide translocase
Transport protein that exchanges matrix ATP for cytosolic ADP (inner membrane is impermeable to ATP)
Cost for transportation of ATP
1 H+/ ATP transported
of ATP/NADH2
2.5 ATP
of ATP/FADH2
1.5 ATP
Glycerol phosphate shuttle mechanism
NADH reduces dihydroxyacetone phosphate to glycerol 3-phosphate, which then transfers electrons to membrane-bound FAD
Malate-aspartate shuttle mechanism
Complicated process which uses malate (toward matrix), aspartate (toward cytosol), and redundant enzymes to shuttle 2 electron packets from NADH to the matrix
