isomers

HURDLE NUMBER 7. THE ISOMER HURDLE.

Two chemicals can have the same formula, (ie:- the same number of atoms of each element), and yet can have different shapes, because the atoms are arranged differently in each chemical. In that case, these two chemicals would be ISOMERS of one another. Many organic chemicals come in various isomers, ie:- one particular type of sugar may come in a variety of different shapes (or isomers), but it is the same type of sugar in terms of its actual formula.

If the simple basic chemicals of life emerged from the primordial soup, then cobbling them together to make more complex molecules would be prevented because the “wrong” isomers would connect up together, and create a non-functional molecule. With so many different isomers of each basic chemical, it would be impossible to proceed further. Here are some quotes from authoritative sources that substantiate the 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, page 47:-

Croft explains how creating a dinucleotide (ie:- two nucleotides joined together) involves several processes.

(1). An organic base has to join with a sugar (ribose), forming a nucleoside.

(2).The nucleoside combines with phosphoric acid to form a nucleotide.

(3).Two nucleotides join together to form a dinucleotide.

Croft then points out that in the above reactions, there are “a large number of possible isomers at each stage, so much so that it is difficult to see how a uniform nucleic acid (ie:- DNA or RNA) could result.”

The next quote is from the same book, page 49:-

“The second problem with the spontaneous formation of nucleotides is the large number of possible isomers that may result when phosphate is added to a nucleoside - - - - the number of possible isomers formed - - - -is extremely large. To suggest that these monomeric nucleotides, existing in a variety of isometric forms could polymerize (ie:- join together) to give a nucleic acid (ie:- RNA or DNA) - - - is completely implausible.”

The next quote is from the same book – page 50:-

“Ribose (a constituent of RNA and DNA) is a pentose sugar - - - - -with ribose there are EIGHT DIFFERENT ISOMERS POSSIBLE (My capitals), making a grand total of FORTY EIGHT DIFFERENT POSSIBLE ISOMERS FOR EACH NUCLEOTIDE FORMED. How could such a mixture of nucleotides polymerize to give a uniform polymer?” (My capitals.)

Croft then quotes A.G. Cairns Smith (Senior Lecturer in Chemistry at The University of Glasgow) who has concluded that the formation of a nucleic acid (ie:- RNA or DNA) on the primeval Earth is a “gigantic implausibility.”

(My comment:- This above information provides material for an interesting probability theory calculation. The smallest protein has about 50 amino acids, and therefore requires a “chain” of DNA 150 nucleotides long to “code” for it. Each nucleotide has 48 different possible isomers. To get the “correct” isomers of EVERY nucleotide in this “chain” would be vastly improbable. The odds against an entirely “successful” “chain” is one chance in 48¹⁵⁰ which is equal to odds of one chance in 10²⁵⁰

ie:- one chance in 1 followed by 250 zeros!

If there were only just one nucleotide that was the “wrong” isomer, the “chain” of RNA or DNA would be non-functional.)

The next quote comes from the book Blueprint For a Cell: The Nature and Origin of Life by Christian de Duve (Professor Emeritus at The Rockefeller University, and President of the International Institute of Cellular and Molecular Pathology), Published by Neil Patterson Publishers 1991, page 134:-

“Consider - - - - the synthesis of RNA - - - - the most optimistic models have to postulate multiple steps, each afflicted by low yields, and many side reactions. By the end of the sequence (of steps) only extremely minute amounts - - - of correct polynucleotides can be expected to be present, SWAMPED BY A HOST OF MOLECULAR MISFITS.” (my capitals.)

(My comment:- By the term “molecular misfits” he is referring to the host of “wrong” isomers of nucleotides that would scupper any attempt to create a viable length of RNA or DNA.)

The next quote is from the book Origins of Life (revised edition) by Freeman Dyson (Emeritus Professor at The Institute For Advanced Studies in Princeton), published by Cambridge University Press, 1999. Pages 24 to 26:-

Dyson explains that RNA is composed of a string of nucleotides – and a nucleotide is composed of three components:-

(1). A nucleotide base.

(2). A sugar (ribose).

(3). A phosphate ion.

Dyson then comments:-“Even more severe difficulties arise - - - - to stick the three parts together IN THE RIGHT GEOMETRICAL ARRANGEMENT. If the linkages are made at random, ONLY ONE IN A HUNDRED MOLECULES WILL BE STEROCHEMICALLY CORRECT. ONLY THE CORRECTLY LINKED MOLECULES CAN POLYMERIZE TO MAKE NUCLEIC ACIDS. It is difficult to imagine a prebiotic process that could separate a correctly formed nucleotide from its 99 MISSHAPEN BROTHERS.” (My capitals.)