The Early Earth Atmosphere and Early Life Catalysts - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 10

Elucidating the origin of biological homochirality has occupied a central
position on studies of the origin of life since the discovery of chiral symmetry by
Pasteur [ 23 , 24 ]. There is, however, no consensus on how an initial small bias for
handedness arose and how a slight excess of handedness led to such a dominance of
biological evolution on Earth. Researchers in this area have agreed to redefine the
question of how homochirality arose into a search for an advantage factor that was
capable of ensuring a large quantitative excess of one of the enantiomers over the
other [ 24 ]. There exist many diverse suggestions for the nature of advantage factors,
but they can be globally grouped into two classes, local and global. Local advantage
factors might have existed in a particular region on the Earth's surface. They could
have varied from region to region and/or might have existed during a definite period
of time. On the other hand, global advantage factors are caused by the parity
nonconservation in weak interactions. The action of the advantage factor might,
in principle, lead to an almost chirally pure state of the medium [ 25 ].

Figure 4 Structural model of a B-DNA right-handed double helix. The structural formula for
2-deoxy-D-ribofuranose (top), and D-ribofuranose (bottom) are shown on the left. They are the
sugar components in DNA and RNA, respectively. The carbohydrate-phosphate “backbone” in the
DNA dodecamer is highlighted in black. Hydrogen bonding between complementary bases is
shown with dotted lines. Redrawn using the sequence PDB CODE 156D reported in [ 49 ].

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