Electron Transport Flashcards
What is the ETC?
A series of four protein complexes that transport electrons to oxygen and pump protons to create a proton gradient
Electrons in NADH and FADH2 are stored at a very ____________ reduction potential.
Negative, they want to react and release them to a more positive reduction potential
T or F: NADH has a more negative reduction potential than FADH2.
True
What is the name of complex I? what inhibits complex I?
NADH DH, rotenone
What is the substrate for complex I?
NADH
Describe the mechanism of complex I.
Takes 2e- from NADH, moves through iron sulfur clusters & FMN & ultimately pumps 4 protons out, transfers e- to complex III via QH2
Does FMN or Fe-S clusters get the electrons first?
FMN (required since NADH donates 2e- and ferric iron only accepts 1e- at a time)
What is the name of complex II? What is it also a part of? Where is it located?
Succinate DH, TCA cycle, Inner mitochondria membrane
Where is complex II located?
Mitochondrial membrane
What is the substrate for complex II?
FADH2
What are four flavoproteins that reduce Coenzyme-Q in the ETC?
Complex I, Complex II, ETF-QO, sn-glycerophosphate DH
Does complex II contribute directly to the proton gradient?
No, it only contributes e- to the Q pool, NO PROTONS ARE PUMPED
Where do electrons from the glycerol shunt enter the ETC?
Complex II (FADH2)
Is Q lipid soluble?
Yes’ that the whole purpose of using it to shuttle electrons through the mitochondrial membrane
Describe the structure of complex III
Rieske Iron, and two b hemes, Cytochrome c1 on cytosolic side
What is unique about electron flow in complex III?
The electron pair from QH2 is split, one travels to the rieske iron center which has a very positive dE(290mv, recall that dG=-nJdE so very spont. Rxn), another e- travels to heme bL (low potential heme, -20mv), this happens because iron center can only accept 1 e- at a time
What happens to the e- that goes to the rieske iron center?
(526) Is passed on to cyt c1 and goes onto Complex IV
What happens to the e- that goes to bL?
Is passed on to bH, then passed to a fully oxidized UQ at the N side of CIII, forms semiquinone that is fully reduced upon addition of 1 more e- (next rxn. ) passes QH2 into the Q pool
Describe movement of protons in complex III.
Each time 1 e- is moved through cycle it releases 2H+ via initial binding, and picks up 2H+ from matrix via bL pathway, however since QH2 provides 2 e- each cycle of the Q cycle in complex III produces a net 4H+ into the cytosol and 2H+ out of the matrix
What binds at the N side of complex III and inhibits it? P side?
Antimycin, stigmatelin, respectively
Describe Complex IV (Cyt c oxidase)
Secretes 2H+ into cytosol, binds oxygen in active site and uses it as a terminal electron acceptor, contains 4 cyt c proteins
How does complex IV pump protons?
(531)Takes 4e- to reduce oxygen, 4 cyt c proteins bind e- on interior of protein, in order to compensate for this thermodynamically unfavorable placement of charge inside a hydrophobic area we also pump 4H+ into it
Describe the path of electrons through complex IV
Cyt cCopper Aheme aheme a3Copper B
Why are there two hemes in complex IV?
Charge compensation, you would think that e- would flow directly to heme, however since we need to compensate for the large charge on the interior we move protons via one heme and electrons via another
Describe the formation of reduced oxygen (water) from Complex IV
Two electrons donated via copper B (one for each metal) and forma peroxide bridge (Fe-O-O-Cu), following this two protons come in and cleave the oxygen bond; two more electrons are dumped in to finish the reduction to water
Do the protons that reduce oxygen follow the same routes as those pumped ?
No, different pathways
What portion of the ATP Synthase structure is embedded in the inner mitochondrial membrane?
F0 Subunit
What is the purpose of the Aspartate residue on the C-Subunit?
**This is the Key of proton transport**
When the aspartate residues of the two C-Subunits are in contact with the hydrophillic environment of the two half channels they give up their protons so they are in the charged aspartate form.
The key to proton transport is that in a proton rich environment such as the cytoplasm of the mitochondria a proton will enter a half channel of the A subunit and bind to aspartate.
The A subunit then rotates until the aspartic acid is in the proton poor environment of the matrix where the proton will then be released.
What powers the rotation of the C-Ring?
The transfer of protons from high concentration on the cytoplasmic side of the mitochondrial membrane to the proton poor region in the matrix of the mitochondria.
Describe the structure of the A subunit of ATP synthase.
The A subunit is composed of two half channels that allow for interaction of protons with the C-Subunit’s aspartic acid residue. It is located in the F-0 portion of ATP synthase.
What subunitis the rotation of the C subunit attached to, the crankshaft of ATP Synthase. (If it were a Rolls Royce Merlin it would be the prop reduction drive.)
The gamma subunit which will be rotated through the Alpha and Beta subunit much as a camshaft will drive the open and closing if intake and exhause valves.
What portion of ATP synthase holds the F-1 subunit stationary while the Gamma subunit rotates?
Alpha Beta and Delta subunits.
What does the energy created in the proton gradient directly contribute to in the ATP synthesis reaction.
Rotation of the Gamma subunit in the stationary F-1 complex (the camshaft) and this causes a conformational change in the alpha and beta subunits of the F-1 complex that is used to release newly synthesized ATP from the tight binding sites.
Where is the ATP synthase located in relation to the cristae of the mitochondria? Does this contribute to its efficency?
They are located in rows on the tips of the cristae of the mitochondria. This greatly increases the efficency of the ATP synthase
Electrical gradient is much greater where the cristae make this sharp turn
