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Origin of Life
In order to more clearly
understand the problems
surrounding the origin of life a
determination of the chemical
compounds involved must be
made. A brief review of
chemistry is necessary.
As was pointed out earlier in
the textbook all living
organisms are made up of
proteins which in turn are
made up of amino acids in a
particular order.
The model shows
that the structure of
the compound is
centered around a
carbon atom. The
chemical compound
making up the R
Group determines
the type and name of
the resultant amino
acid.
Think Critically
Since any compound with the
proper valence can attach at
the R Group site how many
different amino acids do you
estimate are possible?
It is estimated that there are
more than 2,000 different
amino acids.
What percentage of these are
considered to be biologic?
Further examination of
the amino acid model
reveals that the position
of the amino and
carboxyl groups can be
switched. This means
that the shape of the
amino acid can be
changed even though
the chemical equation
remains the same.
.If the shape of the
amino acid changes
then the shape of the
protein changes.
This means that two
proteins are possible
even though they have
the same chemical
equation.
It is now apparent that
the shape of the amino
acid is not only
controlled by the R
Group but also the
relative positions of the
amino and carboxyl
groups to a line drawn
through the R Group
and the Hydrogen
atom.
Chemical Compounds That Have
the Same Chemical Formula But
Differ in Structure Are Called
“Isomers.”
The Two That Are Involved In the
Quest For The Origin of Life Are
Sugars and Amino Acids. They
Are Called “Optical Isomers.”.
Right Handed
Left Handed
Right handed and left handed
molecules occur naturally in
EQUAL NUMBERS.
But a problem exists because Living
organisms use only ONE OR THE
OTHER of these molecules.
Amino Acids Are All Left Handed
Sugars Are All Right Handed.
If only ONE of the wrong
handed molecules gets into
the chain of either amino
acids or sugars the result is
a non-biologic compound.
Think Critically
If a Right Handed Amino
acid gets into a chain of Left
Handed amino acids why
isn’t the resulting protein
useful biologically?
Think Critically
Right Handed sugars are
connected to the bases in the
DNA. What happens when a
Left Handed sugar connects
to a base?
The DNA is
unable to coil
up
successfully.
Think Critically
What is the likelihood of a
primordial soup containing only
biologic amino acids?
What do the L and D type
molecules and the great number
of possible amino acids have any
effect on the origin of life
concept? Support your answer.
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