Question

Consider an ATP synthase having twelve C-rings to sense proton motive force. The average number of protons required per ATP synthesis is _ _ _. (in integer)

Hint:

For ATP synthase: \[ \text{Protons per ATP} = \frac{\text{Number of }c\text{-subunits}}{3} \] because one full rotation generates \(3\) ATP molecules.

Answer 1

Correct Answer: 4

Step 1: Understand the structure of ATP synthase.
ATP synthase contains a rotating \(c\)-ring in the \(F_0\) portion. Protons moving through the membrane rotate this ring and drive ATP synthesis in the \(F_1\) portion.

Step 2: Recall the ATP yield per rotation.
One complete rotation of the ATP synthase rotor produces
\[ 3\ \text{ATP molecules} \] because the \(F_1\) head contains three catalytic sites.

Step 3: Determine the number of protons per full rotation.
If the ATP synthase has \(12\) \(c\)-subunits (C-rings), then one complete rotation requires
\[ 12\ \text{protons} \]

Step 4: Relate proton flow to ATP synthesis.
During one complete rotation:
\[ 12\ \text{protons} \rightarrow 3\ \text{ATP} \]

Step 5: Calculate protons required per ATP.
\[ \frac{12\ \text{protons}}{3\ \text{ATP}} = 4\ \text{protons per ATP} \]

Step 6: Interpret the result.
Thus, on average, synthesis of one ATP molecule requires the movement of
\[ 4 \] protons across the membrane.

Step 7: Final conclusion.
Therefore, the average number of protons required per ATP synthesis is
\[ \boxed{4} \]