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49 Cards in this Set

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What is hydrogen cyanide?
It is a deadly gas that kills cells by blocking the electron transfer from cytochrome oxidase in complex IV to oxygen
What does the electron transport system do?
It converts redox energy available from oxidation of NADH and FASH2 into proton-motive force which is used to synthesize ATP through comformational changes in the ATP synthase complex through a process called oxidative phosphorylation
Oxidation of NADH and FADH2 in the mitochondrial matrix by the ETC links redox energy to ATP synthesis by oxidative phosphorylation through what?
Through the establishment of a proton H+ gradient
What is the end-product of the ETC?
The net result of these redox reactions is the coupled oxidation of NADH and reduction of molecular oxygen (1/2 O2) to form NAD+ and H2O.
What does the difference in reduction potential between the NADH/NAD+ conjugate redox pair and that of the 1/2 O2/H2O conjugate redox pair provide?
It provides a huge amount of free energy for ATP synthesis
What is the basic idea of chemiosmotic theory?
It is that energy from redox reactions or light is translated into vectorial energy through the coupling of electron transfer to membrane bound proton pumps that transverse a proton impermeable membrane and thereby establish an electrochemical proton gradient.
When is a proton circuit established?
It is established when the protons respond to the chemical and electrical gradient across the membrane by flowing back across the membrane through the ATP synthase protein complex to catalyze ATP synthesis
The vectorial H+ gradient results in what?
A chemical gradient across the membrane
What is represented by the chemical gradient?
A change in pH as well as an electrical gradient
What is a critical feature of the mitochondrion?
The extensive surface area of the inner mitochondrial membrane, which forms the proton-impermeable barrier required for chemiosmosis
What does the electron transport system/oxidative phosphorylation accomplish for the cell?
It generates ATP derived from oxidation of metabolic fuels accounting for 28 out of 32 ATP (88%) obtained from glucose catabolism.
What is the overall net reaction of NADH oxidation by the coupled electron transport and oxidative phosphorylation pathway?
2 NADH + 2 H+ + 5 ADP + 5 Pi + O2  2 NAD+ + 5 ATP +2 H2O
What are the key enzymes in the electron transport and oxidative phosphorylation pathway?
ATP synthase complex
What does ATP synthase complex do?
It is the enzyme responsible for converting proton-motive force (energy available from the electrochemical proton gradient) into net ATP synthesis through a series of proton-driven conformational changes.
What is NADH dehydrogenase also known as, and what does it do?
It is also called complex I or NADH-ubiquinone oxidoreductase. This enzyme catalyzes the first redox reaction in the electron transport system in which NADH oxidation is coupled to FMN reduction and pumps 4 H+ into the inter-membrane space.
Whatis Ubiquinone-cytochrome c oxidoreductase also known as, and what does it do?
It is also called complex III, translocates 4 H+ across the membrane via the Q cycle and has the important role of facilitating electron transfer from a two electron carrier (QH2), to cytochrome c, a mobile protein carrier that transfers one electron at a time to complex IV.
What is Cytochrome c oxidase also known as, and what does it do?
It is also called complex IV pumps 2 H+ into the intermembrane space and catalyzes the last redox reaction in the electron transport system in which cytochrome a3 oxidation is coupled to the reduction of molecular oxygen to form water (1/2O2 + 2 e- + 2 H+ --> H2O).
What is an example of the electron transport system?
Cyanide binds to the heme group in cytochrome a3 of complex IV and blocks the electron transport system by preventing the reduction of oxygen to form H2O. Hydrogen cyanide gas is the lethal compound produced in prison gas chambers when sodium cyanide crystals are dropped into
Name each of the 4 complexes of the ETC:
Complex I
Complex II
succinate dehydrogenase
Complex III
Ubiquinone-cytochrome c oxidoreductase
Complex IV
cytochrome c oxidase.
How many electrons are donated by NADH and FADH2 and where do they go?
Pairs of electrons (2 e-) are donated by NADH and FADH2 to complex I and II, respectively
What are the two mobile electron carriers in this series of reactions called?
They are coenzyme Q (Q), also called ubiquinone, and cytochrome c which transfer electrons between various complexes.
What are the four functional components of the electron transport system are:
Three large multisubunit protein complexes, I, III and IV
What do the large multisubunit protein complexes, I, III and IV do?
They transverse the inner mitochondrial membrane and function as proton "pumps".
What is coenzyme Q and what does it do?
It is a small hydrophobic electron carrier that diffuses laterally within the membrane to donate electrons to complex III.
What do the FAD-containing enzymes do?
They pick up electrons from linked metabolic pathways and donate them to coenzyme Q.
What is cytochrome c and what does it do?
It is a small water-soluble protein that associates with the cytosolic side of the membrane and carries electrons one at a time from complex III to complex IV.
How is the energy released by redox reactions used to "pump" protons into the inter-membrane space?
It is thought to involve, 1) a redox loop mechanism in which there is a separation of the H+ and e- on opposite sides of the membrane
What does complex I do?
Complex I passes the two electrons
What three critical roles in the ETC does Q have?
Q serves as a mobile electron carrier that transports electrons laterally in the membrane from complex I to complex III
What is complex II known as and what does it do?
Succinate dehydrogenase is a citrate cycle enzyme. It catalyzes an oxidation reaction that converts succinate to fumarate in a coupled redox reaction involving FAD.
Where are the 2 electrons extracted from succinate in the citrate cycle passed through the other protein subunits to?
They are passed through the other subunits in the complex to Q
Are protons translocated across the inner mitochondrial membrane by complex II?
No
What is the reason that the ATP currency exchange ratio for FADH2 oxidation is lower than it is for NADH, giving rise to only ~1.5 ATP/FADH2 instead of ~2.5 ATP/NADH?
The electron pair donated by succinate to FAD ultimately leads to the translocation of four fewer H+ than NADH because complex II is not a proton pump.
What is complex III known as and what does it do?
Complex III is known as Ubiquinone-cytochrome c oxidoreductase.
What is the first step of the Q cycle?
Oxidation of QH2 at the QP site results in transfer of one electron. The second electron is transferred to cytochrome bL which "stores" it temporarily. The oxidation of QH2 in this first step contributes 2 H+ P to the inter-membrane space.
What is the second step of the Q cycle?
oxidized Q molecule moves from the QP site to the QN site through a proposed substrate channel within the protein
What is the third step of the Q cycle?
A new QH2 molecule binds in the vacated QP site and is oxidized in the same way as step 1
What is the fourth step of the Q cycle?
The second electron from the QH2 oxidation in step 3 is passed directly from bL to bH and then used to reduce the semiquinone Q•-
Write out the two separate QH2 oxidation reactions and them sum them to get the net reaction for complex III
QH2 + Cyt c (oxidized) ---> Q•- + 2 H+P + Cyt c (reduced)
Explain how the 2H+n imbalance is corrected by complex IV?
The imbalance of 2H+N is corrected by the redox reactions of complex IV where 2H+N are required to reduce oxygen to water and 2H+n are pumped across the membrane.
What is cytochrome C and what does it do?
It is a small protein of ~13 kDa that associates with the cytosolic side of the inner mitochondrial membrane and is responsible for transporting an electron from complex III to complex IV using an iron-containing heme prosthetic group.
What is complex IV and what does it do?
Complex IV is Cytochrome c oxidase.
How many protons are required to transport a Pi molecule into the matrix?
1 H+P is required
Define the chemiosmotic theory
It was first proposed by Peter Mitchell in 1961 and states that energy cxaptured by coupled redox reactions in the electron transport system is used to translocate (pump) protons across the inner mitochondrial membrane creating a proton-motive force that drives ATP synthesis by proton flow through the F1Fo ATP synthase complex
How many H+ are pumped across the membrane by complexers I, II, III, and IV?
4 H+ for I and III
What is the role of coenzyme Q in the ETC?
It is a hydrophobic molecule that functions as a mobile electron carrier that transports a pair of electrons in its reduced form of QH2, from either complex I, or from membrane-bound FADH2-containing enzymes such as succinate dehydrogenase or glycerol-3-phosphate dehydrogenase, to complex III