L4: Oxidative Phosphorylation and ATP Synthase

Flashcards covering oxidative phosphorylation, electron transport chains, reactive oxygen species, and ATP synthase mechanism based on the lecture notes.

What is the primary function of electron transport chains?

To transfer electrons from a donor to a terminal acceptor using a series of membrane-embedded protein and lipid carriers.

Which electron carriers are considered 'hydrogen carriers' and why?

Flavins and quinones, because they accept both protons and electrons.

Which electron carriers accept electrons only?

Iron-sulphur proteins and cytochromes.

In bacterial electron transport chains, what is the role of Complex I?

It is NADH dehydrogenase, through which NADH-derived electrons enter the chain.

What is the function of Complex II in the bacterial electron transport chain?

It is succinate dehydrogenase, catalyzing the oxidation of succinate to fumarate and feeding succinate-derived electrons into the quinone pool.

How does the flow of electrons down the electron transport chain generate proton motive force?

As electrons flow, the free energy released is used to pump protons out of the cell, creating an electrochemical gradient.

What is the significance of the Q cycle in the electron transport chain?

It increases the magnitude of the proton gradient by expelling four protons and consuming two cytoplasmic protons for every four electrons transported through Complex III.

In aerobic respiration, what is the terminal electron acceptor and what is it reduced to?

Molecular oxygen (O2) is the terminal electron acceptor, reduced to H2O.

Name three partially reduced oxygen species (ROS) that can escape during aerobic respiration.

Superoxide radical, hydrogen peroxide, and hydroxyl radical.

How do reactive oxygen species cause damage to cells?

They are free radicals that can initiate reactions damaging DNA, proteins, and lipid molecules, and propagate further destructive radicals.

What is the role of antioxidants like vitamin C or flavonoids?

They form stable radicals that do not participate in chain reactions, allowing them to quench or neutralize more destructive radicals.

Which two enzymes do aerobic bacteria use to dispose of reactive oxygen species?

Superoxide dismutase and catalase.

Why can obligate anaerobes not tolerate oxygen?

They lack the enzymes (superoxide dismutase and catalase) necessary to dispose of reactive oxygen species.

What are the two main components of ATP synthase?

The membrane-embedded Fo component and the peripheral F1 component.

Which parts of the ATP synthase are static and which parts rotate?

The 'a' subunit, 'b' subunit, and the α3β3 complex are static, while the 'c' ring rotates and turns the 'γ' subunit.

Describe the journey of a proton through the Fo component of ATP synthase to drive rotation.

A proton enters an outer half-channel of the 'a' subunit, neutralizes an aspartate on a 'c' subunit, allowing the 'c' subunit to rotate into the membrane's hydrophobic phase. After a complete rotation, the protonated aspartate reaches an inner half-channel exposed to the cytosol, where the proton is released into the cell.

What conformational changes occur in the β subunits of ATP synthase during ATP synthesis?

Each β subunit cycles through three states: loose binding of ADP and Pi, tight binding where ADP and Pi condense to form ATP, and release of ATP.

How can ATP synthase function in reverse?

It can hydrolyze ATP to drive proton efflux, switching the direction of continuous rotation to generate proton motive force rather than consuming it.

For what purposes do bacteria surviving by fermentation still need proton motive force?

For flagellar rotation and for nutrient uptake by proton symport mechanisms.