From self-assembled vesicles to protocells

Abstract

Self-assembled vesicles are essential components of primitive cells. We review the importance of vesicles during the origins of life, fundamental thermodynamics and kinetics of self-assembly, and experimental models of simple vesicles, focusing on prebiotically plausible fatty acids and their derivatives. We review recent work on interactions of simple vesicles with RNA and other studies of the transition from vesicles to protocells. Finally we discuss current challenges in understanding the biophysics of protocells, as well as conceptual questions in information transmission and self-replication.

Figure 1.

Diversity of morphology and composition of self-assembled vesicles. Top: Schematic representation of possible morphologies and shape changes. Vesicles may be multi-, oligo-, or unilamellar. They may also be multivesicular (containing smaller vesicles inside a large vesicle). Under certain conditions and for certain amphiphiles, vesicle shape changes can be induced (e.g., leading to vesicle budding and fission). Vesicles may also be nonspherical (e.g., tubular). The diameter of vesicles may vary between about 30 nm and more than 100 µm. Bottom: Vesicle formation occurs for a large number of chemically diverse amphiphiles, including those naturally occurring in biomembranes as well as completely synthetic amphiphiles. Of particular interest are single-chain amphiphiles (or mixtures of amphiphiles) that are potentially prebiotic.

Figure 2.

Structures of prebiotically plausible single chain amphiphiles and a commonly used buffer. (A) micelle; (B) vesicle; (C) myristoleic acid; (D) bicine; (E) geranylgeranyl phosphoric acid; (F) n-decylphosphonic acid.