Saturday, November 21, 2020
We have no idea how life on Earth began
My late Aunt, Dr Jean Youatt (1925-2017), was a very well-respected
microbiologist in Australia;
recognised by the Australian Acadamy of Science in 2000 for her
ground-breaking achievements as a female scientist. Don't ask me why now but, it has occurred that this would be a good place to
post the eponymous item that she wrote many years ago but only sent me in the
year before she died. I believe it speaks for itself:
This outline needs knowledge of Chemistry and Biochemistry to follow the
arguments. A non-scientist will need to refer to literature or consult
knowledgeable people.
Evolutionary biologists avoided this difficult subject even after structures
of proteins and nucleic acids became well known. But it has been admitted by
Professors Davis, Reese and Dawkins recently on TV that we have no idea how
life on earth began. The simplest form of life that can reproduce itself is a
bacterium and for one of them to form there would have to be together in one
place the many components required for one bacterium. There has to be a wall
which separates the organism from its environment and all the walls we know
are complex structures with polymers involving proteins, lipids and
polysaccharides. Inside the cell there have to be proteins and nucleic acids.
The nucleic acids consist of long chains of sugars ribose in RNA and D ribose
in DNA linked by phosphate ester bonds and for each sugar molecule a purine or
pyrimidine base is attached to the sugar and it takes three of these bases to
code for each amino acid in a protein.
We consider the structure of RNA. Ribose is a sugar with 5 carbon atoms. If
it is drawn as an open chain it has 3 chiral atoms (related as mirror images)
and thus 23 different structures possible = 8. In the nucleic acid structure
the sugar is in a ring form and two rings are possible and known. Forming a
ring makes a new chiral centre raising our possibilities to 16 but the ring
can be made of 5 or 6 atoms so now 32 possibilities and then with RNA there
are 2 ways the phosphate ester linkage can form so 64 possibilities. In the
living cell the ribose rings are all identical and there are millions of them
needed in just one cell. The deoxyribose of DNA forms a 5 membered ring too
but has one less chiral atom and one way to form the phosphate link so 16 ways
to form and this too requires millions of identical forms in the DNA.
In the code for making proteins there are just 5 bases used and they must be
in a specific order to define a proteins structure. The atoms which form the
bases could come together in many other forms further increasing the huge
number of atoms which have to form in such a specific way.
"Similarly when we come to consider proteins there are 16 common amino acids
but many other possibilities and proteins which can have 200 amino acids have
to have them in the right order to perform their function. There may be 2000
proteins required. Amino acids formed by chemical reaction which are always a
mixture of 2 chiral forms, that is molecules related to each other as mirror
images which cannot be superimposed. Proteins use only one of these two forms
commonly referred to as the L form. The D and L forms have all the same
chemical and physical properties and so cannot be separated by any common
methods. They can be separated by using reaction with other chiral atoms which
form by enzyme reactions in living cells and in no other way. Sometimes
partial separations have been claimed but not when everything used has been
rigorously freed of all organic compounds and the medium kept sterile
throughout the experiment.
Now we have to assume that all the essential structures are in one place at
one time because if they form by chemical reactions the processes are
reversible. This may suffice to show that for a viable organism to come
together there is an astronomical number of alternative structures from which
just one must come. It is worth mentioning that for 60 years or more
scientists have made mixtures of L amino acids, D sugars, vitamins, purine and
pyrimidine bases etc required to grow human cells and cells have been grown
without any reports of new life forms emerging. Thus for the scientist asking
“Did life emerge by chance or was there a creator?” the only position possible
is “I don’t know” and individuals can choose a creator or chance theory to
their taste.
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