Stage 3 - electron transfer and oxidative phosphorylation Flashcards
Where does electron transfer and oxidative phosphorylation take place?
Mitochondria
What is released from the oxidation of NADH/FADH2 and is used to synthesize ATP by ETC
energy
What does O2 provide? positive and negative?
an energy source but also uncontrolled oxidation
The oxidation of reduced cofactors produce a large and negative delta G. Why?
bcs O2 is a good oxidizing agent
Why is NADH delta G more negative than FADH2?
bcs its a stronger reducing agent
Reoxidation of NADH and FADH2 is broken into smaller steps using…
reducing equivalents of the reduced cofactors
What is the ETC comprised of?
electron carriers in the order of increasing reduction potential - O2 is last (least negative)
and
enzymes which are electron carrier complexes that catalyze the transfer of 1 electron carrier to another
Electron carriers - CoQ
What can it accept?
What does it collect?
can accept 1 (transfer of an H atom)(semiquinone) or 2 electrons (transfer of a hydride ion) to form the alcohol ubiquinol
reducing equivalents
Electron carriers - Cytochrome C
What does it shuttle? from where to where?
How many electrons does it carry at once?
How does it do this?
family of proteins with an iron heme prosthetic group
shuttles electrons from complex 3 to complex 4 of ETC
1 electron
direct transfer as reduction Fe3+ to Fe2+
Complex 1 enzyme
what does it do?
NADH dehydrogenase
transfer electrons to Q causing Q to reduce to QH2
Complex2 enzyme
Why does it enter chain later?
What does it NOT do?
succinate dehydrogenase
enters chain later because weaker reducing agent than NADH
pump protons to IMS
Complex 3 enzyme
what does it do?
cytochrome C reductase
QH2 passes electrons to cytochrome C
Complex 4 enzyme
what does it do
cytochrome oxidase
transfers electrons from reduced cytochrome C to Q2
What is the electron flow through complex 1, 2 and 4 accompanied by?
proton flow from matrix to IMS
Electron transport chain summary
NADH->Q->cytochrome C->O2 (FADH2 enters at Q)
If an inhibitor is placed anywhere on the chain before it gets ______ and after it gets ______
reduced, oxidized
Complex 1 inhibitors
rotenone barbiturates
complex 3 inhibitors
animycin A
complex 4 inhibitors
carbon dioxide, cyanide
What is the proton gradient?
energy available through oxidation of NADH/FADH2 throughout the ETC
How many protons does complex 1, 2 and 4 produce?
4,4,2
If one FADH2 is oxidized how many protons are made?
6
What kind of energy is the proton motive force made of?
- Chemical potential energy - difference in [H+]
- Electrical potential energy - separation of charges
What does chemiosmotic theory explain?
obligatory coupling seen between electron transfer and ATP synthesis
What is chemiosmotic theory?
Free ___ from ____ reactions is used by the ETC to pump _____ moving H+ from the _____ to the ___. Energy is stored as ______ _______. The energy of the electrochemical gradient is released and used for ______ of _____ _____ by the ATP enzyme.
energy, redox, protons, matrix, IMS
electrochemical gradient
generation, ATP synthase
What does inhibition of electron transfer do?
stops ATP synthesis and O2 consumption
What does inhibition of ATP synthase do
stops ETC because energy required to pump protons across this gradient will eventually exceed the available energy from NADH oxidation
no pump protons = no ETC
What happens when the reactions are uncoupled?
IMM is disrupted, therefore protein gradient eliminated (no energy to synthesis ATP from ATP synthase enzyme). Electron transport continues but ATP synthesis stops.
Example of an uncoupler Dinitrophenol. Explain what it does.
DNP turns negative and crosses back into IMM delocalizing the aromatic ring therefore collapsing the protein gradient and stopping synthesis of ATP.
What happens to the energy from the proton gradient in the presence of an uncoupler?
energy from proton gradient is not consumed by ATP formation but dissipated as heat.
What does the proton motive force do?
Release ATP from the enzyme
Cyanide (CN-) is an inhibitor of the electron transport chain (ETC). However, the addition of CN- to the mitochondria not only inhibits the ETC but also inhibits ATP synthesis. Explain the reason for this.
Cyanide inhibits complex 4 of ETC which also inhibits ATP synthesis because electrons can no longer be pumped into intermembrane space.
