Inherited Units

It is now widely believed that the first inherited units were RNA, not DNA. For DNA to be the first inherited unit would be assuming too much. DNA is a much more stable molecule than RNA because of complementary base pairing, many hydrogen bonds, proteins that protect the DNA molecule, etc. RNA formed abiotically is capable or self-replicating when a strand is placed in a solution with monomers. The RNA sequences that are produced are about 5 to 10 nucleotides long. When they added zinc to the solution, they obtained sequences up to 40 nucleotides long and with less than 1% error. Not bad!

• Diagram how a strand of RNA could self-replicate using complementary base pairing.

We now know that modern cells use RNA catalysts called ribozymes. Among other things, they remove introns from RNA. They catalyze the formation of transfer RNA, messenger RNA and ribosomal RNA. Scientists now believe that RNA served both as rudimentary genes and organic catalysts.

If the RNA could weakly bind amino acids, they could combine to form polypeptides. We do know that one function of RNA is to hold amino acids in close proximity so a peptide bond can form. If you let your imagination go wild and assume that the polypeptide was an enzyme that helped the replication of RNA, then you now have the raw material for replication and translation of genetic information.

• The fourth step in chemical-biological evolution does not include a discussion of the inheritance of structures, including chemicals, found in the matrix of primitive cells. Why?

At this point, one must pose a question about recent discoveries on the planet Mars.

• Why were scientists excited to find evidence that the surface of Mars once contained water?

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