Given their ability to sequester and compartmentalize, membranes are essential to life. But they also pose a problem for life – how do you move bulk material into and out of the cell when the membrane is designed to prevent such flux?

Eukaryotic cells make extensive use of secretory vesicles, small membrane-bound sacs filled with cargo. Yet to transfer the contents of a membrane-bound vesicle across the plasma membrane of a cell would require some form of membrane fusion as a transitional stage. Recently, scientists have recorded a critical step in this fusion known as hemifusion. The process of hemifusion is illustrated below.

From here.

I’m struck by the beauty of the process and the manner in which the phospholipid bilayer seems poised to undergo this union. This leaves me wondering if the lipid bilayer is especially well “designed” for such a process.

If so, consider the importance of hemifusion.

This process is likely to be “a common intermediate in many, if not all, biological fusion reactions.” [Here] It is not only involved in exocytosis and endocytosis (which in turn make hormonal control possible), but is also involved in such complex processes as fertilization and communication between neurons. Yet according to conventional thinking, the phospholipid bilayer emerged very early on, as proto-life forms were getting off the ground. Thus, I suppose it would be quite “lucky” that the material used to sequester primitive biochemistry on the strange and primitive earth would turn out to be so handy when it comes to the control and reproduction of complex, multi-cellular life forms that would appear billions of years later.