Respiration Flashcards
What is respiration carried out by?
Electron transfer chains
What is redox potential?
Effectively a measure of the tendency to donate electrons
Where are the three sites of energy conservation?
(ie where there is a significant change in redox potential) Between complexes I and II, III and IV, IV and O2
What are the postulates of the chemiosmotic hypothesis?
Coupling membrane is permeable to water but not to protons and other ions (low electrical conductivity)
Respiratory chain is an alternating sequence of H and electron carriers; arrangement is such that oxidation of substrates results in translocation of protons from one side of the membrane to the other
The ATP synthase (ATPase) is a reversible, proton-translocating, membrane-bound enzyme complex
The proton gradient can be used to support other energy-requiring functions eg solute accumulation, flagellar rotation
What does is a redox loop and what does it do?
It is made of a hydrogen carrier and electron carrier
When the H carrier passes electrons to electron carrier, accompanying protons cannot be accepted so are released
When the electron carrier passes the electrons to the next H carrier, protons are also required and so are recruited from the environment
Protons are released and taken up from opposite sides of the membrane, so effectively 2 H+ are translocated for every 2 e-s passed along the chain
How do redox pumps translocate protons?
As a result of a round of conformational changes in response to electron binding, followed by proton binding, electron release and proton release
Why is energy required for proton translocation?
So protons can be moved against a prevailing gradient
What is the number of protons translocated determined by?
The amount of energy released during electron transport and the size of the transmembrane proton gradient
Also dependent on the composition and spatial arrangement of the electron transport chain, since this is what provides the means to move protons across the membrane
What is the most efficient terminal electron acceptor and why?
Oxygen, because the O2/H2O redox couple has a much higher redox potential than alternative electron acceptors
Since the amount of energy by the electron transport chain is proportional to the redox potential difference between the original electron donor and final electron acceptor, respiration using oxygen releases more energy
In what direction do electrons spontaneously flow?
From low (more negative) to high (more positive)
What is the protonmotive force made up of?
Membrane potential, pH gradient
