27 - Electron Transport and Oxidative Phosphorylation Flashcards
NADH and FADH2 are produced by what 3 processes?
Glycolysis
Fatty acid oxidation
TCA cycle
What is the final acceptor of the electron transport chain?
O2
What happens in oxidative phosphorylation?
The electrons from NADH and FADH2 (2 each) reduce the O2 (final acceptor in ETC) to H20 and drive the formation of ATP the movement of protons down their concentration gradient, driving the formation of ATP from ADP with the enzyme ATP synthase
The inner membrane of the mitochondrion is protein-rich. It is impermeable to what and permeable to what (in general terms)?
Impermeable
- Metabolites (eg. ATP, ADP)
- Ions (eg. H+, phosphate)
Permeable
- O2, H2O and CO2
Where does electron transport and oxidative phosphorylation take place in the mitochondrion? Where do protons accumulate to build the proton gradient?
The inner membrane
Protons accumulate in the intermembrane space
What do:
- FMN (flavin mononucleotide)
- Coenzyme Q/ubiquinone (CoQ)
- Iron-sulfur cluster (FeS)
- Heme α
Do?
These molecules transport electrons
How are electron carriers in the ETC arranged in the inner membrane?
In order of increasing electron affinity
How many components of the ETC are there? What does each function as?
There are 4 complexes and one cytochrome C, each acts as an oxidoreductase.
What is the path electrons take through the electron transport chain? (Just list complex numbers or symbols)
NADH - I - UQ - III - Cyt C - IV -O2
FADH2 - II - UQ - III - Cyt C - IV - O2
List the complexes (5) of the ETC and their prosthetic groups
Complex I (NADH dehydrogenase) - FMN, FeS
Complex II (succinate dehydrogenase) - FAD, FeS
Complex III (Cytochrome bc1 complex) - Hemes, FeS
Cytochrome C
- Heme
Complex IV (cytochrome oxidase) - Heme, Fe, Cu
What does complex I (NADH dehydrogenase) of the ETC do?
Catalyzes transfer of electrons from NADH to ubiquinone (UQ)
Electron movement is accompanied by a net movement of protons from the matrix to intermembrane space
What does Ubiquinone (coenzyme Q) do? What is it?
It is a lipid-soluble mobile electron carrier that can transfer electrons one at a time.
What is the nutritional supplement known as CoSQ10 (Q10)?
The form of ubiquinone with 10 isoprenoid units
What does complex II (succinate dehydrogenase complex) do in ETC?
Transfers electrons from succinate via FAD to UQ
It is also the path of electrons from succinate, glycerol-3-phosphate and fatty acids to UQ
Where can UQ get electrons from in the ETC?
- Complexes I and II
- Fatty Acyl-CoA oxidation
- Glycerol-3-phosphate dehydrogenases
What does complex III (cytochrome b1) of the ETC do?
- Transfers electrons from reduced coenzyme Q (UQH2) to cytochrome C
What are cytochromes?
Proteins with a heme prosthetic group. Electrons can change the oxidation state of heme iron between Fe+2 and Fe+3 (like in ETC)
It is water soluble and a mobile carrier in the outer face of the inner mitochondrial membrane
What is complex IV (cytochrome oxidase) of the ETC and what does it do? What regulates it and how?
Oxidizes 4 cytochrome C molecules (taking one electron from each) and each set of 4 electrons allow the reduction of one O2 to H2O
ATP can act as an allosteric inhibitor of cytochrome oxidase by binding to complex IV and cytochrome C
What happens to the energy levels of electrons as the flow through the ETC?
As electrons flow through the ETC they release energy (used to pump protons into the intermembrane space, establishing a proton gradient to generate ATP), meaning that they decrease in energy with every step of the ETC.
How many molecuels of ATP are synthesized from NADH?
2.5
How many molecules of ATP are synthesized from a FADH2?
1.5
What does the fluid-state model of the ETC describe?
Describes electron transport between ETC components at random collisions
What does the solid-state model of the ETC describe? Why is this model more efficient than the fluid-state model?
Recent research indicates a respirasome, a supercomplex of I, III and IV
In this model electron transfer is considered to be highly efficient because of short diffusion distances.
What is the chemiosmotic hypothesis of oxidative phosphorylation?
Protons accumulated in the intermembrane space generate an electrochemical gradient. When protons travel down the gradient across the membrane back to the matrix (chemiosmosis), this proton-motive force is harnessed by ATP synthase to convert ADP to ATP, sometimes ATP synthase is called complex V
Protons are pumped in what direction across crista membrane (in ETC) to establish proton gradient? In which direction do they mechanize ATP synthase?
They are pumped into crista space from the ETC, going down their concentration gradient drives oxidative phosphorylation at ATP synthase
What is F1F0-ATPase?
ATP synthase
What is the F0 substructure of ATP synthase? What antibiotic blocks it?
A transmembrane portion that is blocked by the antibiotic oligomycin
What is the F1 substructure of ATP synthase?
A water-soluble peripheral portion that extends into the matrix. This is where ADP is phosphorylated
How many rotors turn when protons pass through the ATP synthase?
2
What subunit of the F1 particle houses the ADP and ATP?
Τηε β subunit. Can be in open (O), tight (T) and loose (L) conformations
What are the steps in ATP synthesis at ATP synthase?
- ADP and Pi bind to L (loose) site, rotation converts it to T (tight) conformation
- ATP synthesized
- Rotation converts T site to O (open) site, releasing ATP
What are effects of uncouplers (such as dinitrophenol and ionophores such as gramifidin A)?
They disrupt the proton gradient, inhibiting ATP synthesis
How much ATP is yielded from the oxidation of one molecule of glucose?
31
