The building blocks for RNA are
called nucleotides. A nucleotide consists of 1 phosphate group attached to a ribose which
in turn is attached to one of the four bases, uracil, cytosine, adenine or guanine.
In the case of proteins, the amino acid is the smallest building block. No
condensation reactions are required to create amino acids. In contrast, two condensation
reactions are required to create a nucleotide . One to attach the phosphate to ribose and
one to attach one of the bases (adenine, guanine, uracil, and cytosine) to the ribose
(figure 8.10).
Under optimal conditions, adenine and guanine can be attached to ribose in the lab. The
procedure involves dry heat and sea water. Nucleotides that use cytosine and uracil have
no plausible mechanisms to attach the base to ribose.10
Figure 9.8: Condensation Reaction (Subunits of RNA)
Activated Monomers
Condensing agents are popular for peptide synthesis. They are also effective for RNA
synthesis, but in the case of RNA, the nucleotides are usually directly activated before
being added to the mixture. In the presence of clay, such activated monomers have been
shown to form chains greater than 50 nucleotides long.16 The most popular activation agent
is impA and is shown in figure 9.9. To form impG, impC, and impU replace the adenine with
the appropriate base. The source of these activated molecules is unclear. They would have
not been present in the soup, so when researchers add them to test tubes in high
concentration and then claim that their experiment models the origin of the life, their
claim is without merit.
Figure 9.9: ImpA
Next: Review of Investigator Intereference
Previous: Pre-RNA World |
