Electron transport chain and oxidative phosphorylation - Part 2 Flashcards
What are the two sides of NADH DH called?
N - inside - matrix
P - peripheral - outside
What is the active site for NADH on complex 1?
Matrix arm
Where is the binding site for coq10 on NADH DH?
In the membrane
Transfer from NADH to FMN in NADH DH is done as what?
Hydride ion
Can coq10 in NADH DH only take one electron?
No, takes one electron from Fe-S center and then waits for the other, allowing it to leave.
How does Coq10 (reduced) get to complex 3?
Simple diffusion following a concentration gradient
What does electron transfer from NADH to coq10 do to complex 1?
Causes a conformational change which leads to pumping out of 4 protons.
In complex 2, succinate DH transfer electrons from ______ to ____ which then transfers to ____.
succinate –> FAD –> coq10
FAD becomes FADH2 during the ______ DH reaction in the CAC.
succinate
What other DH is present at the same site as complex 2 leading to electron transfer to coq10?
FA-CoA DH
What are the three ways that electrons are transferred from FADH2 to coq10?
1 - FA
2 - Succinate DH
3 - Glycerol-3-phosphate DH
Complex 2 has three parts, these are?
1 - Succinate DH
2 - ETF:Q oxidoreductase
3 - G3P DH
In complex 3, what occurs to Coq10?
Reduced and oxidized
Describe the Q cycle.
QH2 (ubiquinol) comes to complex 3.
Gives away two electrons in the form of electron-proton pair and protons pumped out.
The acceptors are both ferric ions (Fe3+) and can only accept one electron at a time.
The leftover protons become orphans and are pumped out of the mt membrane.
One electron acceptor is Fe-S, the other is cytochrome bl.
Iron-sulfur center then transfers to cytochrome c1, then to cytochrome C which then gets fully reduced, leaves for complex 4 and gets replaced.
From cytochrome bl, transferred to cytochrome bh, then back to oxidized coq10 - semiubiquinone now.
Semiubiquinone stays there. Meanwhile, another QH2 arrives and performs the same cycle.
Partially reduced coq10 receives another electron, fully reduced but, needs protons, finds a proton pair from inside the matrix and takes them. the cycle continues and two protons are pumped out.
Total of 4 H+ pumped out.
In complex 4, also called _______ _ ______, there are three subunits.
What does each one contain?
Cytochrome c oxidase
Subunit 1: contains two heme groups (a and a3) and a Cu ion (CuB)
Subunit 2: CuA and Cyt c binding site
Subunit 3: role not understood but essential for function
Where is the binding site for cyt C on complex 4?
unit 2
Copper and iron centers can accept how many electrons, respectively?
1 each
For an oxygen molecule to be reduced, how many electrons does it need?
4
What is unit 3 required for in complex 4?
What happens if it’s defective?
Holding oxygen in place, doesn’t release it until fully reduced.
Can get superoxide radical.
If starting with NADH, how many oxygen atoms will be reduced?
Molecules?
1
1/2
From one NADH, if only two electrons, how many protons pumped out?
2
How many molecules of oxygen get reduced by FADH2?
atoms?
1/2
1
What is the chemical coupling hypothesis?
What are its problems?
Oxidation coupled to ATP synthesis.
Energy is conserved through the formation of a high energy intermediate (similar to 1,3-BPG) which can be used to generate ATP.
Problems:
1 - No high energy intermediate detected
2 - Breaking the mt membrane blocks ATP synthesis
What is the conformational-coupling hypothesis?
What were the problems with this hypothesis?
Electron transport oxidation energy conserved in the form of conformational energy which can be used to synthesize ATP.
Problems:
1 - No evidence for ET proteins making ATP
2 - Breaking the inner mt membrane blocks ATP synthesis
What were Mitchell’s observations for the chemi-osmotic hypothesis?
1 - intact mt membrane required for oxidative phosphorylation
2 - inner mt membrane impermeable to H+, K+, OH- and Cl-
3 - ET –> results in transport of H+ out of mt –> electrochemical gradient
4 - Compounds that increase permeability to mt membrane dissipate the electrochemical gradient
(allow electron transport but inhibit ATP synthesis)
What was the chemiosmotic hypothesis?
Oxidation and electron transport generates an electrochemical gradient across the mt membrane through proton transport whose energy can be used to synthesize ATP.
What were the two proposed mechanism of H+ transport?
Redox loop mechanism
Proton pump mechanism
What was the redox loop mechanism?
Similar to Q-cycle
In each complex where oxidation occurs, carrier picks up protons from the matrix and, during the process of transfer, release the protons to the outside.
Only sufficient for 2 protons being pumped.
What was the proton pump mechanism. What was its support?
During redox rxn in ETC components, reduction causes conformational change which decreases the pKa of the side chain, exposing it to the outside thereby dissociating protons.
Reoxidation restores the original conformation.
Its support came from the proton pump in bacterial rhodopsin.
Light driven conformational change which led to release of protons outside
What were mitchell’s experiments that led to him winning the Nobel prize?
1 - Coupling of ET to ATP synthesis - any inhibitor of ETC complexes also inhibits ATP synthesis
2 - Experiments to show uncoupling of ETC to ATP synthesis
What were the two things monitored in Mitchell’s experiments?
Oxygen consumption and ATP synthesis.
Draw the graphs showing Mitchell’s experiments, coupling and uncoupling.
Explain each point as well.
Refer to notes.
