Lecture 12: ATP Synthesis

What drives ATP synthesis in mitochondria?

Proton motive force generated by ETC; proton flow back through ATP synthase, driving ATP formation

What does “chemiosmotic coupling” mean?

“Osmotic” = proton gradient; “Chemi” = ATP synthesis

What are the 2 main components of ATP synthase? 

F_o rotor (membrane-bound) and F₁ unit (matrix side) 

Function of F_o subunits? 

a subunit = proton channel; c subunits = rotor; 3 H+ → 120^o turn, 9H+ → full rotation 

How is rotation induced?

Protonation of glutamate disrupts electrostatic interactions → c-ring rotates

What does the F₁ unit do?

Converts mechanical rotation into conformational changes to synthesis ATP

3 conformation of alpha-beta subunits? 

Open (O) — unbound. Loose (L) — ADP + Pi bound. Tight (T) — ATP bound 

How many H+ needed for a full rotation?

9H+ → ATP (3H+ per ATP)

Energy from proton motive force?

~-21.5 kJ/mol per proton

Energy to make ATP? 

~55-60 kJ/mol. → 3H+ required for one ATP synthesis 

Total proton cost per ATP including transport?

4 H+ (3 for ATP synthase + 1 for Pi import)

Proton contribution from NADH vs FADH2?

NADH = 10 H+ → 2.5 ATP; FADH = 6 H+ → 1.5 ATP

Why does bacterial ATP yield differ? 

No need for Pi import or ATP export (no extra proton cost) 

How many ATP are generated from 1 glucose using malate-aspartate shuttle?

Glycolysis (cytosolic NADH via shuttle) + PDHC + TCA → total ~32 ATP

ATP synthase =

F_o rotor + F1 catalytic head

NADH yields…

2.5 ATP; FADH2 yields 1.5 ATP 

What does coupling ETC to ATP synthase do?

Maintain energy efficiency