Which factor most directly enhances transcellular transport?

Which factor most directly enhances transcellular transport?

• A. High lipophilicity
• B. High molecular weight
• C. Low membrane permeability
• D. Hydrophilicity

Answer: (A)

Transcellular transport is driven mainly by passive diffusion through the lipid bilayer of cells. Molecules that are highly lipophilic readily partition into the membrane, increasing their ability to diffuse across from one side of the cell to the other. This membrane partitioning is what directly boosts transcellular transport. In contrast, large molecules face steric barriers and diffuse more slowly, and hydrophilic compounds don’t partition well into the lipid core, so their transcellular crossing is limited. Ionization at physiological pH can further reduce crossing, since ionized forms are less likely to partition into the membrane, whereas nonionized, lipophilic forms cross more readily.

Transcellular transport is driven mainly by passive diffusion through the lipid bilayer of cells. Molecules that are highly lipophilic readily partition into the membrane, increasing their ability to diffuse across from one side of the cell to the other. This membrane partitioning is what directly boosts transcellular transport.

In contrast, large molecules face steric barriers and diffuse more slowly, and hydrophilic compounds don’t partition well into the lipid core, so their transcellular crossing is limited. Ionization at physiological pH can further reduce crossing, since ionized forms are less likely to partition into the membrane, whereas nonionized, lipophilic forms cross more readily.