The origin and amplification of chirality

Many biological molecules such as, sugars, amino acids and nucleic acids, are chiral molecules. This means that of these molecules two mirror images exist. Surprisingly, in nature only one mirror image of the two possible mirror images, also known as enantiomers, is present. It would be thermodynamically more favourable to have a racemic (fifty-fifty) mixture of enantiomers. The presence of only one enantiomer in nature, known as homochirality, poses a big mystery. Because nature’s building blocks, amino acids and sugars, are chiral, the structures that are based on them, such as proteins and DNA, are therefore chiral. One of the functions of proteins is to catalyse chemical reactions. Proteins with this function are called enzymes. Since enzymes are chiral themselves, they are capable of maintaining the homochirality of life. If by accident a molecule of the wrong chirality would be present it would not be selected by the enzyme, as it does not fit. One can imagine these enzymes to be left gloves that have a pocket that fits a left hand and is therefore selective for left hands.Before life emerged, no enzymes were present to select the correct enantiomer. This makes the origin of homochirality comparable to the chicken and egg problem: which came first, homochirality or life? Generally it is assumed that homochirality emerged before life; it has even been mentioned as a prerequisite for life. In this thesis several mechanisms are investigated to achieve homochirality under prebiotically viable conditions.

Dissertation: http://hdl.handle.net/11370/866ad66d-2a02-4c0a-b391-8c2cdeda8557