Question

Q1. Earlier models of membrane transport models suggested that transport proteins binds a solute molecule or ion on one side of the membrane and then diffuse across the membrane to release the solute molecule on the other side. This transverse carrier model is later proven to be wrong. Suggest two reasons that argue against transverse carrier model. One of your reasons should be based on our current understanding of membrane structure and the other on thermodynamic considerations.

Answer 1

carrier mechanism implies that the molecule binds to the transport protein (carrier), at the outer surface of the cell, and that this complex rotates and translocates the molecule into the cytoplasm. firstly the rotation and translocation are unlikely to occur in view of what is known about the organisation of the cell membrane. secondly, rotation is thermodynamically difficult, and the translocation of the a macromolecule from one half of the bilayer to the other is even less likely to occur.