ETC & ATP Synthase

Question 1

What are the key components of the ETC? What do they do?

Answer 1

Complex 1: Transfers electrons from NADH to ubiquinone (CoQ)
Complex 2: Transfers electrons from succinate (via FADH2) to ubiquinone
Complex 3: Transfers electrons from ubiquinol to cytochrome c
Complex 4: Transfers electrons from cytochrome c to oxygen
Ubiquinone (CoQ): Acts as an electron holder to transfer electrons from complex 1 and 2 to complex 3
Cytochrome c: Transfers electrons from Complex III to Complex IV.

Question 2

Where does ETC take place?

Answer 2

The components of the ETC are embedded in the inner mitochondrial membrane

Question 3

What are the benefits of having the ETC occur where it does?

Answer 3

Proton Gradient Creation (drives ATP synthesis in the ATP synthase complex)
Compartmentalization (Separates Citric acid cycle and ETC)
Efficient Electron Transfer (prevent the loss of energy as heat)

Question 4

What is the driving force for the ETC?

Answer 4

The driving force of the ETC is the redox potential (E°’).

Question 5

What is the pathway of the ETC?

Answer 5

-NADH donates electrons to Complex I, reducing ubiquinone (CoQ) to ubiquinol (CoQH2).
-FADH2 donates electrons to Complex II, which passes them to ubiquinone (CoQ) also reducing it
-Ubiquinol carries electrons to Complex III, where they are transferred to cytochrome c, reducing it.
-Cytochrome c carries electrons to Complex IV, where they are transferred to oxygen, reducing it to water.

Question 6

What is the ultimate electron acceptor in the ETC?

Answer 6

Oxygen

Question 7

What is the overall purpose of the ETC?

Answer 7

This whole process makes ATP

Question 8

What is Proton Motive Force (PMF)?

Answer 8

The proton motive force (PMF) is the “pressure” created by the movement of protons (H⁺ ions) across the mitochondrial membrane during electron transport.

Question 9

How Does Proton Motive Force Link Electron Transport and ATP Synthesis?

Answer 9

PMF causes protons to want to flow back inside with the gradient but must use ATP synthase.

Question 10

What are the two main subunits of ATP synthase? What do they do?

Answer 10

F₀ Subunit (Membrane Component): Forms a channel in the membrane for H+ to move through causing rotation which causes a conformational change in F₁
F₁ Subunit (Catalytic Head): Divided into three more subunits that carry out ATP synthesis, allow ADP and inorganic phosphate (Pi) to bind, form ATP