lecture 28 - How ATP is Synthesized at “Energy Coupling” Membranes: Chemiosmotic Coupling

Question 1

How is ATP Synthesis Coupled to the

Redox Reactions?

Answer 1

Phosphorylation is energized indirectly, via generation of
a H+ potential across the inner mitochondrial membrane:
NADH–> NAD+
½O2 + 2H+ –> H2O

Question 2

What is the chemiosmotic hypothesis?

Answer 2

1. The coupling complexes in the redox chain are H+ pumps.
2. Low membrane permeability to H+ allows build up of transmembrane H+
   potential.
3. Passive return of H+ across membrane energises ATP synthesis

Question 3

Describe F- type ATP synthase

Answer 3

Two sectors: F0 and F1
F0 section in cytoplasm
F1 in matrix contains ADP binding site for ATP formation
and rotating section

Question 4

Why do redox reactions speed up when ADP is added?

Answer 4

ADP facilitates flow of H+ through ATP synthase.
This decreases the PMF slightly.
Decrease in opposing driving force enables faster operation of redox coupled H+ pumps.

Question 5

Describe the action of uncouplers

Answer 5

Some compounds (eg 2, 4 dinitrophenol and FCCP)
(i) abolish ATP synthesis “uncouple”
(ii) speed up respiration
Chemiosmotic explanation:
Uncouplers catalyse passive H+ flow (they are “protonophores”) and rapidly abolish PMF. Thus: (i) there’s no longer a driving force for ATP synthesis and (ii) no force opposing redox reactions so they will speed
up!