Question

Oxidative Phosphorylation (McKee 374-378).  

1. Describe how the relatively high concentration of protons are prohibited from returning to the matrix of the mitochondria based on the permeability of the inner mitochondrial membrane
2. Explain the route taken by the proton gradient based on the proton channel of the ATP synthase complex.
3. Describe the location of the rotor portion of the ATP synthase (F₀) based on the membranes and compartments of the mitochondria.
4. Describe how the rotor portion of the ATP turns based on H⁺ flowing though the proton channel.
5. Describe the location of the catalytic sites for ATP synthesis based on the rotor and stator (F1) of the ATP synthase complex.
6. Describe the location of the F1 portion of the ATP synthase complex based on the aqueous compartments of the mitochondria.
7. Describe how the turning rotor transfers the energy required for ATP formation based on conformational changes in the catalytic sites that have substrates, ADP and inorganic phosphate (Pi), bound.
8. Describe how the electron transport chain and ATP synthase complex cooperate in the process of oxidative phosphorylation

Answer 1

1. Very high concentration of protons is prohibited from returning to the matrix of the mitochondria due to the impermeability of the inner mitochondrial membrane towards hydrogen ions.

2. The proton gradient generated by proton pumping during the electron transport chain is a stored form of energy. When protons flow back down their concentration gradient (from the intermembrane space to the matrix), their only route is through ATP synthase, an enzyme embedded in the inner mitochondrial membrane.

3. Fo portion of the ATP synthase is embedded within the membrane of the mitochondria (in eukaryotes), thylakoid membrane of the chloroplast (only in plants), or plasma membrane (in prokaryotes).

4. Located within the mitochondria, ATP synthase consists of 2 regions: the FO portion is within the membrane and the F1 portion of the ATP synthase is above the membrane, inside the matrix of the mitochondria. Membrane-integrated F_o portion has three different subunits, a ₁b ₂c_n(n; variable among species) and mediates proton transport across the membrane.

5. The c-subunits forms a ring structure, and ab ₂ associates with the c-subunit ring peripherally. When the magnitude of the electrochemical potential of protons is large enough, downhill proton flow through F_o causes rotation of the rotor subunits (c _n-γε) relative to the stator subunits (ab ₂-α₃β₃δ), and rotation of the γ-subunit forces the β-subunits of F₁ to change conformations sequentially that result in ATP synthesis.