chirality

HURDLE NUMBER 13. THE CHIRALITY HURDLE.

The Chirality Hurdle is a very serious obstacle to the formation of the molecules of life in the primordial soup. In that case, I should provide some definitions of terminology used in this context. Most organic molecules are either “Left-Handed” or “Right-Handed” molecules. If a group of all left handed molecules join together, they are said to have the same CHIRALITY, ie:- they are CHIRALLY UNIFORM, or CHIRALLY HOMOGENEOUS. If left-handed and right-handed (ie:- L and D) molecules join together, they form a RACEMIC compound, otherwise known as a RACEMATE. Compounds that are chirally uniform can be identified as such by optical means, and are referred to as being OPTICALLY ACTIVE.

The basic problem is this:- All biological proteins are CHIRALLY UNIFORM. All DNA molecules in biological life-forms are CHIRALLY UNIFORM. If a protein contained just one single amino acid molecule with the “wrong” chirality, then that protein would not “work” properly. If a DNA molecule contained just one single nucleotide with the “wrong” chirality, then that DNA molecule would not “work” properly. In the primordial soup, molecules join together with “higgledy-piggledy” chirality, ie:- Right handed molecules will shamelessly combine with left handed molecules in a manner that absolutely subverts any possible biological function. Here are some quotes from authoritative sources that substantiate this above statement:-

This quote is from the book How Life Began by L.R. Croft, Lecturer in Biological Sciences at The University of Salford, published by Evangelical Press, 1988, pages 55 to 61:-

“Most chemical reactions normally proceed with no regard to chirality - - - - - Chemical reactions in the laboratory provide only racemic compounds - - - - Enzymes - - - - are proteins that depend precisely on their three-dimensional structure for activity. Thus a protein made up of racemic amino acids could not adopt a specific shape, and so could have no biological activity - - - - A random mixture of L and D (ie:- left handed and right handed) amino acids in an enzyme molecule - - - - could have no activity. Without chiral uniformity a protein would be unable to fold in the same way twice. This it could not be relied upon to have any enzymatic activity - - - - only a chirally uniform nucleic acid (ie:- DNA or RNA) could be functional - - - - The Miller experiment (when electrical; discharge through gases produced amino acids) - - - - produced only racemic mixtures of amino acids. Life is inconceivable based on such racemates - - - - Racemic protein and nucleic acid could have had no activity.”

The next a quote from the book Genetic Takeover and The Mineral Origins of Life by A.G. Cairns Smith (Senior Lecturer in Chemistry at The University of Glasgow), published by Cambridge University Press, reprinted 1987, pages 43 to 45:-

Cairns Smith explains that for a polypeptide (ie:- a chain of amino acids – effectively a protein) molecule of 100 amino acids, there is just one chance in 10 followed by 29 zeros that all the amino acids will be left-handed. If they are not all left-handed, then “with side-chains pointing different ways, this would - - - - - affect the folding (ie:- of the protein), which depends so critically on side-chain packing - - - - Only a chirally uniform nucleic acid (ie:- RNA or DNA) looks as if it could work - - - - - Much of the point of a protein and - - - - nucleic acid would seem to be lost unless these molecules have appropriate secondary/tertiary structures; and that is only possible with chirally defined units. (ie:- if they are chirally uniform).”

The next quote is from the book Molecular Evolution And The Origin of Life by Sidney W. Fox (University of Miami) and Klaus Dose (of The Gutenberg Institute), published by W.H. Freeman and co. San Francisco, 1972, page 123:-

“None of the compounds synthesized in the experiments simulating prebiotic conditions have been reported to be optically active.”

The next quote is from the book Molecular Origin of Life edited by Andre Brack, published by Cambridge University Press, Article:- Origins of The RNA World by Alan W. Schwartz of The Evolutionary Biology Research Group, Faculty of Science, University of Nijmegan, Netherlands, pages 237 to 254:-

(Page 252):- The spontaneous chemical synthesis of even a short structurally and chirally homogeneous oligonucleotide (ie:- a length of

RNA or DNA) is implausible in the extreme.”