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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