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Why are reducing equivalents essential?
allows for the use of a substrate shuttle system to accomplish the net transfer of reducing equivalent across the membrane (these basically shuttle the electrons)
Why are acetyl units essential?
they transport acetyl-CoA indirectly by attaching the acetyl group to oxaloacetate forming citrate, transporting citrate across the membrane, and then transferring the acetyl group back to CoA on the other side of the membrane
Why is ATP essential in terms of mitochondrial transport systems?
ATP/ADP translocase directly transports ATP and ADP across the membrane (antiport transporter), exchanging cytosolic ADP 3- for mitochondrial ATP 4-
Why is Acyl-CoA essential?
carnitine acyltransferase I (located on the outside of the inner membrane) catalyzes the formation of O-acylcarnitine which is them transported across the membrane by a translocase. The fatty acyl group is then transferred back to CoA on the other side of the membrane to re-form acyl-CoA
ΔG* equation in terms of cell potential
ΔG*=-nF(E*cell)
n=number of electrons transferred
Why is electron transport set up to not be 100% efficient?
to release heat to regulate temperature instating of conforming to the temperature of the environment
A spontaneous reaction is indicated by what kind of cell potential
positive cell potential
About how many protons must be pumped to make 1 ATP
4
Complex I
NADH dehydrogenase
transfers pair of electrons from NADH to coenzyme Q
-FMN (flavin) accepts the 2 electrons and then transfers them one at a time to the FeS centers (iron does one at a time 2+→3+) which then gives the two electrons (1:1) to coenzyme Q
-contains an active H+ transporter (4 protons) to pump protons into inter membrane space
Complex II
succinate dehydrogenase (same enzyme as TCA cycle)
contains FAD covalently found to a His residue, 3 FeS centers and a cytochrome b; passes electrons to coenzyme Q
-does NOT transport H+
Complex III
coenzyme Q-cytochrome c reductase
contains 3 different cytochromes and an FeS protein; participates in Q cycle
-technically no H+ transporter in complex III but uses coenzyme Q being reduced to QH2 to dump those to protons off into the inter membrane space
-electrons are passed (1:1) to cytochrome c (the only water-soluble cytochrome)
Q cycle
-QH2 from complex I binds to cytochrome b in Complex III, releasing 2 H+ molecules into the inter membrane space and passing the 2 electrons to cytochrome b subunits (1:1)
-the two electrons cycle through the cytochrome b subunits and get passed back to coenzyme Q, which will pick up 2 more protons and release those into the inter membrane space and then give the 2 electrons to FeS which gives them to cytochrome c (peripheral membrane protein; loosely attached to membrane)
What starts apoptosis in your cells?
cytochrome c going into the cytosol
-when cytochrome c detaches from membrane, it means that electron transport isn’t working so cell=dead
Complex IV
cytochrome c oxidase
contains two heme centers (cytochrome a) and two copper atoms (+1→+2)
shuttles electrons to final electron acceptor (O2) to make water
-has an H+ transporter (2 protons) to pump into inter membrane space
-copper doesn’t generate as much energy (has less reducing potential) so that is why it doesn’t transport as many protons
Reduction of one oxygen molecule requires the passage of how many electrons?
4 (one at a time)
Bacteriorhodopsin
hydrogen transporter similar to the one you find in complex I
-transports protons by giving them to an aspartate, which then moves inside the membrane (no longer has negative charge with hydrogen on it)
-water environment down the middle of the transporter so aspartate residues keep picking up the protons and undergoing 3D structure changes, and passing them along until they reach the other side of the membrane (inter membrane space)
-glutamates or arginines can be used as well
ATPase
F0: nonpolar portion that sits in the membrane
F1: polar/water-soluble portion inside the mitochondria
-huge multi-protein complex
beta subunit: catalytic part that does the reaction for you; 3 beta subunits total
alpha subunit: regulatory domains
c (in F0): passive hydrogen transporter;
3D structure changes to release energy (Asp→Arg)
gamma subunit stalk
Inhibitors of complex I
-Rotenone: insecticide that prevents reduction of coenzyme Q
-Amytal: barbituate; prevents reduction of coenzyme Q
-Demerol: pain-killer
NADH doesn’t work but FADH2 does with these
Inhibitor of Complex III
antimycin A: antibiotic that blocks the electron transfer from coenzyme Q to cytochrome b
no ATP from NADH or FADH2
Inhibitors of Complex IV
-Cyanide: binds tightly to Fe3+ of cytochrome a
-Carbon monoxide: binds tightly to Fe2+ of cytochrome a
-Azide: binds tightly to Fe3+ of cytochrome a
no ATP from NADH or FADH2
Uncoupling agents and what they cause
2,4-dinitrophenol (2,4-DNP) and pentachlorophenol
-ATP goes down and metabolism goes up (electron transport, oxygen usage, and TCA cycle all increase but not as much ATP is being produced)
-used as a diet drug: releases heat
-big half-life so must be highly regulated
**Natural uncoupling proteins are generally found in brown fat (i.e. infants)
Oligomycin
inhibits ATP synthase
-stops electron transport→decrease in ATP
-not using O2 so this inhibits TCA cycle as well and all aerobic respiration essentially stops
Antioxidants
destroy free radicals
-enzyme=superoxide dismutase (SOD) which takes radicals and turns them into hydrogen peroxide
-catalase (enzyme) takes the hydrogen peroxide and converts it to water and oxygen
-glutathione peroxidase takes the hydrogen peroxide and converts it to GSSG and water
