Oxidative phosphorylation

Where does oxidative phosphorylation occur?

Cristae of mitochondria

What happens in oxidative phosphorylation overall?

The energy carried by electrons, from red. NAD & FAD, is used to make ATP

Electron transport chain

• Found on inner membrane of mitochondria (cristae)

• Composed of 4 complexes + 1 ATP synthase embedded in membrane

Chemiosmosis

The process of ATP production driven by the movement of H+ ions across a membrane (due to the movement of electrons down an electron transport chain)

Chemiosmotic Theory (model for oxy-phos)

• Energy from e^- passed thru ETC is used to pump H+ up their electrochemical gradient into intermembrane space

• H+ then allowed to flow by facilitated diffusion thru a channel in ATP synthase into matrix

• Energy of H+ flowing down electrochemical gradient is harnessed

  • Results in phosphorylation of ADP into ATP by ATP synthase

Process of Oxidative Phosphorylation

1. red.NAD & red.FAD arrive at ETC ; are oxidised to release H which splits into H+ and e^-

2. E^- enter complexes 1 (NAD) & 2 (FAD) and move thru chain to complex 4, losing energy as they do this

3. This energy is used to pump H+ into intermembrane space

4. Proton / H+ gradient created between this space

   • Conc. of H+ higher in intermembrane space than matrix

5. H+ diffuse thru hydrophilic channels of ATP synthase & into matrix, down proton gradient, resulting in synthesis of ATP

   • ADP + Pi → ATP

6. E^- combine w. H+ & O2 to form H₂O

   • 2H+ 2e^- + ½ O₂ → H₂O

What is Oxygen known as and why is it so important?

Final electron acceptor

• Electron chain cannot operate, unless O2 is present, electrons will have no where to go

• No more ATP is produced via oxy-phos

• W.out O2 accepting e^- & H+, red.NAD & FAD can’t be oxidised to regenerate NAD & FAD, so can’t be used in further hydrogen transport

• No oxidised NAD & FAD available for dehydrogenation in Krebs, so Krebs stops

NOTE: Phosphorylation in oxy-phos is dependent on e^- moving along ETCs, requiring presence of oxygen

Why is chemiosmosis not completely efficient?

Some H+ ions leak back into the matrix

Properties of mitochondrial inner membrane that allow chemiosmosis

• Impermeable to H+ , so e^- carriers required to pump H+ across in order to establish H+ gradient

• Large SA

Net products from Oxidative Phosphorylation

• 34x ATP , 38 max

• H2O

Explain why the electrons released form red. FAD lead to the synthesis of less ATP than the electron released from red. NAD

• Red. NAD release electrons to carriers at start of ETC

• Red. FAD releases electron to carriers after start

• W. FAD, electrons are transported shorter distance

• So fewer protons are actively transport