A protocell is a self-organized, self-ordered, spherical collection of
lipids proposed as a stepping-stone to the origin of life.
[169] A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation driving the evolution of life. Although a functional protocell has not yet been achieved in a laboratory setting, there are scientists who think the goal is well within reach.
[170][171][172]
Self-assembled
vesicles are essential components of primitive cells.
[169] The
second law of thermodynamics requires that the Universe move in a direction in which
entropy increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate
life processes from non-living matter.
[173] Researchers Irene A. Chen and Jack W. Szostak amongst others, suggest that simple physicochemical properties of elementary protocells can give rise to essential cellular behaviours, including primitive forms of differential reproduction competition and energy storage. Such cooperative interactions between the membrane and its encapsulated contents could greatly simplify the transition from simple replicating molecules to true cells.
[171] Furthermore, competition for membrane molecules would favour stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the
phospholipids of today.
[171] Such
micro-encapsulation would allow for metabolism within the membrane, the exchange of small molecules but the prevention of passage of large substances across it.
[174] The main advantages of encapsulation include the increased
solubility of the contained cargo within the capsule and the storage of energy in the form of a
electrochemical gradient.