Adpatp Exchanger

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ATP synthase makes ATP inside the mitochondrion. For the ATP to be available to the rest of the cell, there needs to be a mechanism to enable it to leave the mitochondrion for use in the cytosol. This job is performed by another carrier, the ADP/ATP exchanger. This protein has no enzymatic action; it simply moves ADP in one direction across the mitochondrial inner membrane and ATP in the opposite direction. In most eukaryotic cells the carrier operates in the direction shown in Figure 12.3. Carriers such as the Na+/K+ ATPase together with many synthetic processes use up ATP in the cytosol, producing ADP. Then ADP enters the mitochondria by the ADP/ATP exchanger and is reconverted to ATP by ATP synthase. ATP then leaves the mitochondrion with the help of the ADP/ATP exchanger.

Example 12.2

Chemicals That Interfere with Energy Conversion Are Highly Toxic

The electron transport chain, ATP synthase, and the sodium/potassium ATPase together run the energy currency market and are vital to the cell. Chemicals that interfere with them are very toxic. Rotenone, the most widely used rat poison, blocks complex I of the electron transport chain while cyanide blocks complex IV. Digitalis, from foxgloves, blocks the Na+/K+ ATPase.

rotenone cyanide high energy low energy

Electron transport chain digitalis blocks Na+/K+ ATPase rotenone cyanide high energy digitalis blocks Na+/K+ ATPase

low energy

Electron transport chain

ATPase

ATPase

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