Stereoselective Phosphorylation of d-Ribose as a Driver of Life's Homochirality

Life demonstrates remarkable homochirality of its major building blocks: nucleic acids, amino acids, sugars, and phospholipids. Phospholipid bilayer vesicles (liposomes) are formed at the water/air interface from Langmuir layers and contain ribose, a constituent of primordial water. Although the primordial ribose was initially racemic, life, as we know it, is homochiral, with d-ribose and its derivatives as the predominant forms. The phospholipid membrane's permeability to d-ribose, together with ribose's interaction with the bilayer's charged phosphate groups, leads to ribose phosphorylation, yielding d-ribose-5-phosphate. Once inside, the d-ribose-5-phosphate molecules cannot cross the membrane. A similar path also exists for l-ribose, but with a lower rate. Therefore, overall, this process is enantioselective, 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's chirality.