SEARCHING FOR THE ORIGIN OF LIFE

Chapter 3

MIRROR IMAGE MOLECULES

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Question from Chapter 2

Was Miller's amino acid experiment the formula for Spontaneous Generation of life by natural processes alone?

More Theories and Experiments

Since 1953 theories about the earth's atmosphere have changed and by 1983 the prevailing theory was that the "primitive atmosphere" consisted of carbon dioxide and nitrogen, rather than methane and ammonia.  Miller did the experiment again in 1983 using this combination of gases, but produced almost no amino acids.  Jeffrey Bada of Scripps Institute of Oceanography, California, found this version of Miller's experiment produced nitrites, chemicals that destroy amino acids as soon as they form and turn the water acidic, further inhibiting formation of amino acids.  Bada proposed that the primeval earth would have contained iron and carbonate minerals, which would have neutralised the nitrites.  He has now (2007) carried out the experiment again with chemicals that neutralise nitrites and produced amino acids. (See Scientific American, 28 Mar 2007, http://www.sciam.com/article.cfm?articleID=9952573C-E7F2-99DF-32F2928046329479&sc=I100322  )

After more than half a century and many variations of Miller's original experiment, no-one doubts it is possible to produce amino acids by naturally occurring physical/chemical processes.  However, no-one has succeeded in making the theoretical steps from amino acids to living cells into reality.  To do this they must overcome a problem of one natural property of amino acids, i.e. amino acids are chiral molecules.

What are Chiral Molecules?

The atoms which make up each amino acid molecule (except glycine) can be assembled in two slightly differing molecular shapes.  The difference between the two shapes is like the difference between your left and right hands.  Each hand has the same components, arranged in the same way, i.e. one thumb on the side of the palm, and four fingers in a row.  We could write a formula for a hand as T1F4 and this would be equally valid for each hand.  But, have you ever tried putting a right hand into a left hand glove?  Your two hands are not exactly the same.  You cannot substitute a right hand for a left hand.  Hold your right hand up to a mirror and compare the reflection in the mirror to your left hand.  Your left and right hands are mirror images of one another.

Amino acids (and all chiral molecules) have this same property.  Each amino acid has two mirror image forms which have been called right handed and left handed.  The simplest amino acid which shows this property is Alanine.


Left Handed Alanine           Right Handed Alanine

The chemistry involved in making a left or a  right handed molecules is the same, and all experiments to date using natural chemical processes alone, such as Miller's and Bada's, have produced solutions containing an equal mix of right handed and left handed amino acid molecules.

But, here is the big problem!

Amino acids found in the proteins of living cells are exclusively left handed.

Therefore, we must ask the following question:

Are there any natural properties of amino acids that would enable them to form a solution of 100% left handed amino acids? 

To answer this question we need to look at the natural properties of chiral molecules.

It is possible to obtain a solution of the 100% amino acids by extracting them from a proteins made by living cells.  But, if they are left in the solution for natural processes to take their course, the molecules slowly change until the solution becomes an approximately 50/50 right and left handed mixture.  This change is called racemisation and is a Natural Property of all chiral molecules so far observed. 

Racemisation During Life

Racemisation of amino acids occurs quite slowly and proteins inside living cells are usually replaced before any of their amino acids racemise.  However, some proteins are exported from cells and are incorporated into substances that are not replaced throughout your whole life, e.g. the liquid gel (vitreous humor) in your eyeball and the hard dentine inside teeth.  These materials are effectively "non-living" as they are no longer part of any living cell.  Once laid down they become subject to natural processes.  The amino acids in the these deposits undergo racemisation, and in a long lived organism, such as a whale or a human being, a measurable amount of right handed amino acids can be found in the eyes and teeth by the time these creatures reach old age.  The percentage of racemised amino acids in eyes and teeth can be used to estimate the ages of recently dead whales and people.

Racemisation does occasionally happen to proteins within living cells, but it causes the proteins to become non-functional, and the cells usually dispose of them.  If they are allowed to build up, defunct racemised proteins can damage the cell.  Thus, racemisation is a degenerative process.  This is confirmed by what happens to proteins after a living cell dies.

Molecules After Death

After an organism dies all of its amino acids, both inside and outside of cells, become subject to natural processes.  Proteins that were made from left handed amino acids, gradually change into a mixture of left and right handed molecules.  The time it takes any protein's 100% left handed amino acids to alter to 50% right handed amino acids varies with the type of amino acid and with environmental conditions, so this method does not always provide an accurate clock for dating dead things.  However, given enough time such a process will continue until there is an approximately even mixture of the two forms.

A 50/50 mixture of amino acids is as dead as you can get.  Therefore, Miller's, Bada's and other chemical evolution experiments, which produce 50/50 mixes of right and left handed molecules, simulate death - not life!

The effect of Natural Processes (NP) on left handed amino acids can be summarised:

100% LHAA + Time + Energy  NP® 50% LHAA + 50% RHAA

The same process occurs if you start with 100% right handed amino acids.  It also eventually becomes a 50/50 mixture.  In other words natural processes always tend towards mixes of right and left, and away from pure left or right.

Question

If exclusively left handed amino acids are needed to make the proteins of any of earth's living organisms, is there any way of separating the left from the right, or producing exclusively left handed molecules?

How this could be done is the subject of Chapter 4.

SUMMARY OF CHAPTER 3

In order to explain how living cells formed from non-living matter without a Creator, evolutionary scientists proposed that at some time in the past simple molecules combined together to make organic molecules, which then formed the first living cells.  All this occurred by natural processes alone.

Stanley Miller and others have made amino acids, essential building blocks of life, from simple molecules and claimed their experiments represented the first step in producing life from non-living matter.

However, one major problem has barrier to forming living cells starting with amino acids produced by natural process.  Amino acids are chiral, i.e. they come in right and left handed forms. Making amino acids by natural processes always produces a mix of left and right handed forms.  But, the amino acids in the proteins of living cells are all left handed.

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