Oxidative phosphorylation 1 ptB

Main Ideas

ATP synthase converts a proton gradient across the inner mitochondrial membrane into rotation, which drives ATP production.

Rotary Structure

The membrane-embedded c ring rotates and drives the central γ (gamma) rotor. As the rotor turns, its changing shape affects three α–β pairs. The catalytic sites are located on the β subunits.

Three Catalytic Conformations

Each α–β pair cycles through three conformations:

• Open (O): ADP and phosphate can enter, or ATP can be released.
• Loose (L): Bound nucleotides are held in place.
• Tight (T): ADP and phosphate are brought into the state that forms ATP.

How Rotation Produces ATP

As the rotor turns, each catalytic pair changes conformation in sequence. For a pair followed through the cycle, O allows binding, L traps the nucleotides, T promotes ATP formation, and returning to O releases ATP. A full 360° turn produces three ATP molecules, one from each catalytic pair.

How Protons Drive Rotation

The video describes proton flow through the membrane portion of ATP synthase:

1. A proton gradient provides the driving force. The electron transport chain creates a higher proton concentration in the intermembrane space than in the matrix.
2. The a subunit provides two partial channels. One opens toward the intermembrane space and the other toward the matrix. Neither channel passes straight through the entire subunit.
3. Acidic residues in the c ring bind and release protons. Each c subunit has an aspartate or glutamate residue. In the membrane’s hydrophobic environment, these residues can move around the ring more readily when protonated and electrically neutral.
4. Protonation helps turn the c ring. A proton entering from the intermembrane-space side binds to an acidic residue. The neutralized residue moves within the membrane as the c ring rotates.
5. Protons are released into the matrix. When the protonated residue reaches the matrix-side channel, the lower proton concentration there favors the release of the proton. The residue becomes negatively charged again.
6. Repeated binding and release drives continued rotation. Protons enter from the intermembrane-space side, travel around with the c ring, and exit into the matrix. This rotation drives the conformational changes that produce ATP.

The speaker notes that the number of c-ring subunits affects how many protons are required per ATP. Vertebrates are described as having eight c subunits. Fewer subunits mean fewer protons are needed for a full turn, while each full turn still yields three ATP.

Speakers and Sources Featured

• One unnamed instructor/narrator explains the mechanism using diagrams and figures.
• No additional speakers or external sources are identified in the subtitles.