Primordial cells would have been similar in concept and function to this compartmentalization, although they may not have used the same components as present-day cells. Their membrane would most likely consist of amphiphilic molecules such as fatty acids or possibly polyprenyl phosphates, similar to modern archaea. However, having a pure lipid bilayer would result in inadequate exchange of charged ions and large polar molecules between the environment and the cell, especially without the use of transporter proteins. Proposals have been proposed that cell membranes and membrane proteins have co-evolved, in that cell membranes have gone from porous to ion-tight, just as membrane proteins have gone from pore-forming amphiphilic proteins to ion-tight. very hydrophobic integral membrane proteins. A proposed pattern of this membrane-protein co-development involving the increasing complexity of F- and V-type ATPases and sodium ion transporters with membranes porous to protons and sodium ions, becoming more ion-tight, can be seen in Figure 1-5 (Mulkidjanian et al..