Carrier proteins are proteins that span the plasma membrane.Carrier proteins are also called carriers, permeases, or transporters.They bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across the membrane.In one conformation, the carrier protein is open on one side of the membrane and closed on the opposite side. The ion or molecule binds to the protein on one side of the membrane.This causes the shape to change opening the protein on the opposite side to let the ion or molecule through whilst closing the protein behind the ion.