Coacervate
From Wikipedia, the free encyclopedia
A coacervate is a spherical aggregation of lipid molecules making up a colloidal inclusion which is held together by hydrophobic forces. More plainly stated; it is usually a little ball of organic matter which is formed by the repulsion of water by something like an oil.
Coacervates measure 1 to 100 micrometers across, possess osmotic properties and form spontaneously from certain weak organic solutions. Their name derives from the Latin coacervare, meaning to assemble together or cluster. They were even once suggested to have played a significant role in the evolution of cells and, therefore, of life itself.
[edit] How do they form?
In water, organic chemicals do not necessarily remain uniformly dispersed but may separate out into layers or droplets. If the droplets which form contain a colloid, rich in organic compounds and are surrounded by a tight skin of water molecules, then they are known as coacervates. These structures were first investigated by the Dutch chemist H. G. Bungenburg de Jong, in 1932. A wide variety of solutions can give rise to them; for example, coacervates form spontaneously when a protein, such as gelatin, reacts with gum arabic. They are interesting not only in that they provide a locally segregated environment but also in that their boundaries allow the selective adsorption of simple organic molecules from the surrounding medium. In Oparin's view this amounts to an elementary form of metabolism. Bernal commented that they are "the nearest we can come to cells without introducing any biological – or, at any rate, any living biological – substance." However, the lack of any mechanism by which coacervates can reproduce leaves them far short of being living systems.(2)
[edit] The Origin of Life
While proposing that modern life came from common ancestors, with the "tree" of life being simpler the farther back one goes, Charles Darwin suggested that, therefore, all living things may come from a single common ancestor, an "ur-organism", presumably something very simple and primitive. Then the question arises: from whence came that first organism?
Coacervates were actually suggested by Aleksandr Oparin, as a means by which that first "ur-organism" could have formed from non-living, organic matter. He noted that organic chemicals could be formed by the exposure of natural substances to sunlight (ultraviolet radiation, more specifically), in an oxygen-free atmosphere and then would sometimes recombine into larger molecules, until sufficient to form colloids and, therefore, coacervates. Since these coacervates do superficially resemble living cells, Oparin suggested that they eventually became complex enough to be simple life. While this is vaguely similar to modern theories, regarding the formation of first life, coacervates are no longer thought actually to have become the first cells directly; life is thought to have gone through many intermediate steps before becoming cellular.
