Question

Justify whether L-glucose and D-glucose wold be transported across the cell membrane at the same rate.

Answer 1

The binding sites for solute on the transport proteins are stereospecific. For example, the transporter for glucose in the renal proximal tubule recognizes and transports the natural isomer D-glucose, but it does not recognize or transport the unnatural isomer L-glucose. In contrast, simple diffusion does not distinguish between the two glucose isomers because no protein carrier is involved.