Question

Most eukaryotic ABC transporters are involved in exporting small molecules from the cytosol. In this subset of the ABC transporters, does the small molecule bind better to the ATP-bound (B) or the ATP-free transporter?

Answer 1

Small molecules typically bind better to the ATP-bound conformation of eukaryotic ABC transporters, as this state has a higher affinity for the substrates and is part of the cycle of active transport involving ATP binding and hydrolysis.

Step-by-step explanation:

In eukaryotic cells, ABC transporters are crucial for the active transport of small molecules. These transport proteins operate in a cycle that involves binding and hydrolysis of ATP. The small molecule typically binds more favorably to the transporter in its ATP-bound form (B). This conformation allows for a higher affinity binding state compared to the ATP-free transporter, facilitating the transport of the molecule across the membrane. Post-binding, ATP is hydrolyzed, which leads to a change in the transporter's conformation and promotes the release of the molecule on the other side of the membrane.

This process is essential for maintaining proper concentrations of ions and other substances required by cells to function correctly. Since this transport mechanism requires energy in the form of ATP, it is an example of primary active transport, which directly uses cellular energy to move substances against their concentration gradient.