Electron Transport Chain (ETC) - 4.4

Q: Where does the ETC occur?

A: In the inner mitochondria of the cell.

Q: What is the ETC responsible for?

A: The transfer of electrons from NADH and FADH₂ to O₂.

Q: How many protein complexes are in the ETC?

A: Four protein complexes:

1. Complex I – NADH Dehydrogenase

2. Complex II – Succinate Dehydrogenase

3. Complex III – Cytochrome complex

4. Complex IV – Cytochrome oxidase

Q: What are the two electron carriers in the ETC?

A: Ubiquinone (UQ) and Cytochrome c (Cyt c).

Q: What does Ubiquinone (UQ) do?

A: Carries electrons from Complex I to Complex II, and from Complex II to Complex III.

Q: What does Cytochrome c do?

A: Carries electrons from Complex III to Complex IV.

Q: What happens at Complex I?

• Electrons from NADH are brought to complex I

• As electrons move into the complex, energy is released

• The energy from complex I pumps 4 H+ into the inner membrane of the mitochondria

Q: What happens at Complex II?

• UQ takes the electrons from complex I and moves it to complex II

• At complex II, FADH2 is oxidized to FAD+

  • This releases two electrons

• UQ carries all electrons to Complex III

Q: What happens at Complex III?

• Like complex I, electrons move in, causing energy to be released

• The energy released allows a proton pump to occur

• This transfers another 4 H+ into the inner mitochondrial membrane

• Note: There is now a high concentration of H+ in the inner membrane

Q: What is the effect of proton pumping?

A: Creates a high concentration of H⁺ in the inner membrane.

Q: What happens at Complex IV?

• Electron carrier cytochrome c transfers the electrons to Complex IV

• Once again, this facilitates the movement of H⁺ into the inner membrane

  • However, only 2 H⁺ are pumped through

• Oxygen comes and takes a pair of electrons and 2 H⁺

  • This makes H₂O

  • For every O₂ molecule

    • 4 electrons are pulled

    • 2 water molecules are produced

Q: How many water molecules are produced per O₂ molecule?

A: 2 H₂O molecules.

Q: Why does chemiosmosis occur?

A: High H⁺ concentration in the inner membrane creates a proton gradient.

Q: How do protons move across the membrane?

A: Through ATP synthase via facilitated diffusion.

Q: How does ATP synthase work?

A: 3 protons attach, causing it to spin like a turbine, catalyzing ATP production from ADP + Pi.

Q: How many ATP are made per glucose molecule from ETC and chemiosmosis?

A: 34 ATP.