Heuristic model on the origin of the homochirality of life

Life demonstrates remarkable homochirality of its major building blocks: nucleic acids, amino acids, sugars, and phospholipids. We propose a mechanism that places the root of life homochirality in the formation of phospholipid bilayer vesicles (liposomes). These liposomes are formed at the water-air interface from Langmuir layers and contain ribose, presumably delivered to Early Earth by carbonaceous meteorites. Although the extraterrestrial ribose was initially racemic, life is homochiral, based on D-ribose and its derivatives. The phospholipid membrane high permeability to D-ribose, combined with the ribose interaction with the bilayer charged phosphate groups, leads to ribose phosphorylation, forming D-ribose-5-phosphate. Once inside, the D-ribose-5-phosphate molecules cannot cross the membrane. The catalytic action of Fe (3+ions) greatly enhances the phosphorylation rate. Overall, this process is enantioselective, substantially favoring the buildup of D-ribose over L-ribose. Through liposome fusion, fission, and self-replication, this eventually leads to the Darwinian evolution of these structures and to the conversion of D-ribose-5-phosphate into complex functional molecules, such as ribozymes and RNA, and eventually into DNA, all of which inherit D-ribose chirality.