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20 Cards in this Set

  • Front
  • Back
What are the four main steps in converting glucose to ATP?

Where does each step occur?
Byproducts of each?
1) Glycolysis: Cytosol
2) TCA: INTERMEMBRANE space of Mito, CO2
3) E- transfer: Mito inner membrane, H2O
4) Ox-Phos: mito inner mem
How does the mitochondrial innermembrane differ from the outer membrane?
Innermembrane: TIGHT; very little makes it in out

Porous: protons get in/out, big molecules (ex.: proteins) need help
What are cristae and what purpose do they serve?
Cristae are folds in the mitochondrial innermembrane that maximize the surface area for oxidative-phosphorylation to occur in.
To what molecule does NADH transfer its electrons? What products are formed?

Write out the chemical equation for this process.
O2; NAD+, H2O

NADH + H+ + 1/2O2 --> NAD+ + H2O
What purpose does the transfer of electrons from NADH to oxygen serve?
Free energy that accompanies this change used to pump protons across inner membrane, forming a pH gradient to drive ATP synthesis.

Protons will flow from outside membrane to inside, and this is coupled to ATP synthesis.
If deltaG = -nFE and F = 96.5, what is the reduction potential (biological standard) of NADH?

How many ATPs could be synthesized if this reaction occured with 100% efficiency?
How would this reaction contribute to ATP synthesis?
1/2 O2 + 2H+ --> H2O
deltaG=-2(96.5)(.82)=-158 kJ/mol

NADH + H+ --> NAD+ + 2H+ + 2e-
deltaG=-2(96.5)(.32)=-62 kJ/mol

Total deltaG=-210 kJ/mol

Proton pumping (?) is coupled with ATP synthesis
Under what circumstances would an electron use a vacuum to cross a cell membrane?
A protein?
How is this optimized?
If there's no distance to cover, protein and vacuum are equally fast paths.

Once beyond 10 Angstroms, don't use a vacuum, use a protein.

Vacuums provide short distance, proteins provide speed. So electrons utilize "through protein, through vacuum" jumps where they go from protein to vacuum to protein, etc.
How does electron transfer vary as a function of driving force?
It's bow shaped (like an upside down U), so adding more driving force (more negative deltaG) will actually reduce rate of electron transfer. Must be an optimal deltaG (not too high or low) for optimal rate of transfer.
Describe the four complexes electrons must travel through to be transferred from NADH to O2.

In terms of cell location, where are the protons traveling from and to?
NADH to NADH-Q oxidoreductase
to Coenzyme Q (formed by succinate-Q reductase)
to Q-cytochrome c oxidoreductase
to Cyt C
to Cytochrome C oxidase
to O2

From mito matrix to intermembrane space
What class of chemicals does co-enzyme Q belong to? What is notable about this class of chemicals? What does this allow for in terms of electron transfer?

Describe another characteristic of coenzyme Q that contributes to its function. Why is this important in electron transfer?
Quinones have very stable intermediates despite their being radicals.

This allows one electron to come from Q and go to Q one at a time. This is important because NADH is a 2 e- carrier, but Cyt C is a one electron carrier. So Q allows us to convert betwen 2 and 1 electron carriers.

Q has hydrophobic tail which resides in membrane and is mobile by diffusing through fatty acid part of membrane.

Proteins involved in four complexes are membrnae bound complexes so they're immobile. In order for electrons to pass through, they need carriers that are mobile. Mobile carriers are NADH and Coeznyme Q
Where is Cyt C located in the cell?
INNERmembrane space
What is the oxidized form of coenzyme Q? Reduced? What are the chemical names for each of these?
Oxidized: Q, aka ubiquinone
Reduced: QH2, aka ubiquinol
When coenzyme Q is protonated, what does it form? Where do these protons come from? What about when this protonated form is oxidized? What does this result in?
What other molecule contributes to this?
QH2; matrix
Releases proton into intermembrane space.

High pH in matrix, lower pH in cytosol (IM space)

NADH releases protons into IM space.
For Iron-Sulfur clusters, how must reduction potential relate to other specific proteins involved in electron transfer. Why?
Must have reduction potential greater than QH2, but less than Cyt c1 so that overall electron travels from QH2 to cyt c.
How does the reduction potential of Q vary?
higher in Qi site, than when bound in Qo site
What is the chemical equation of the reaction that NADH-Q oxidoreductase catalyzes?

Describe the path of the protons.
NADH + Q+ 5H+(matrix)-->NAD+ + QH2 + 4H+(cytosol)

Two matrix protons go to QH2, NADH proton and other three protons pumped across from matrix to cytosol.
Describe the mechanism of Q-cyt c oxidoreductase.
QH2 is bound to Q0 site (does not bind Q as tightly as Qi), Q binds Qi site.
Electrons transferred from QH2 in two directions and releases 2H+ into IMS:
1) To Fe-S to CytC1 to CytC
2) To Cyt bL to cyt bH to Q in Qi site, forming Q radical

Remember Cyt c can only carry one e- at a time, so can't send both of QH2 electrons to him at once. Reduced Cyt C leaves, oxidized (empty) Cyt c attaches

QH2 enters and binds Qo site, electrons follow same paths as before, except Q radical takes in 2H+ from matrix, becoming QH2.
Now we have Q in Qo and QH2 in Qi site.

To reset, QH2 comes in to kick out Q, and Q comes in to kick out QH2

Four protons pumped out
Describe the mechanism of Cyt c oxidase.
Reduced Cyt C comes and binds. Electron travels to dual copper CuA/CuA site to Heme a to Heme a3 to CuB. Now CuB is reduced.

Empty Cyt c leaves and new one comes (with electron). Electron goes through CuA/CuA to heme a to iron in Heme a3. Iron is now reduced.

O2 enters and forms Fe-O=O, this then forms a peroxide bridge between Fe and Cu (Fe, Cu are now oxidized)

New cyt c!
Electrons follow same path to Fe, and H+ pumped in, cleaving O-O bond and forming Fe=O and Cu-OH

New Cyt c!
Another H+ pumped in and reduces Ferryl group to form Fe-OH

2H+ pumped in and get 2H2O released.

All 4 electrons transferred, and pumped out 4 protons. Repeat.
How many NADH molecules are required to completely give to oxygen?
NADH has 2 electrons, Oxygen needs 4, so need 2 NADH.
Why does electron transfer occur in so many "little steps"?
Rate of electron transfer versus potential is bow shaped. The smaller the chunks we break these transfers down, the better we can apply them (coupling wise)--like gears. DOn't start your car in 4th!