ATP synthase function

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Questions and Answers

Which of the following statements accurately describes the roles of ATP synthase subunits?

The delta subunit is located within the membrane and assists in proton translocation.
The c-ring, embedded in the membrane, contributes to the rotary movement of ATP synthase. (correct)
The b-subunit facilitates the rotation of the hexamer formed by the alpha and beta subunits.
The gamma and epsilon subunits are static components solely for structural support.

During ATP synthesis, what is the primary role of the magnesium ion ($Mg^{2+}$) within the active site of ATP synthase?

It promotes the release of ATP from the enzyme by weakening interactions with the beta subunit.
It stabilizes and neutralizes the charge of the phosphate groups, facilitating nucleophilic attack. (correct)
It directly catalyzes the formation of the phosphodiester bond between ADP and inorganic phosphate.
It facilitates the entry of ADP into the active site by altering the local electrostatic environment.

In the mechanism of c-ring rotation, what drives the directional movement of the c-ring within ATP synthase?

The concentration gradient of protons across the inner mitochondrial membrane. (correct)
Electrostatic repulsion between protons and amino acid side chains on the c-subunits.
Attraction between protons and hydrophobic amino acid side chains.
Mechanical force exerted by the F1 complex during ATP hydrolysis.

Which statement accurately captures the sequence of events during ATP synthesis by ATP synthase?

ADP and inorganic phosphate diffuse into the active site, a phosphodiester bond is formed, and a conformational change ejects ATP. (A) Signup and view all the answers

What prevents the hexamer formed by the alpha and beta subunits of ATP synthase from rotating?

The stalk containing the delta and b-subunits. (A) Signup and view all the answers

How do amino acids contribute to the binding of ADP within the active site of ATP synthase?

They mediate hydrogen bonds that stabilize ADP, especially at the base and, to a lesser extent, the sugar. (D) Signup and view all the answers

Why is the reverse rotation of the c-ring in ATP synthase energetically unfavorable?

Due to the need to move protons against their concentration gradient, from low concentration to high concentration. (A) Signup and view all the answers

What is the direct function of the a-subunit in the rotation of the c-ring of ATP synthase?

It contains channels that facilitate the entry and exit of protons, linking the intermembrane space and the matrix. (B) Signup and view all the answers

How does the entry of inorganic phosphate into the active site of a beta subunit facilitate ATP synthesis?

By inducing a conformational change that promotes a planar transition state. (B) Signup and view all the answers

After ATP is ejected from the active site of ATP synthase, what key event occurs next in the catalytic cycle?

The subunit switches to the open conformation, enzyme resets and synthesis of another ATP molecule can restart. (B) Signup and view all the answers

Flashcards

Turning Subunits

Includes gamma and epsilon subunits; facilitates ATP synthesis.

C-Ring Location

Embedded within the membrane; part of ATP synthase.