The Roles Of

In the early 1980s, researcher Thomas Cech (1947—) found that a type of RNA found in some unicellular eukaryotes is able to act as a chemical catalyst, similar to the way an enzyme acts. Cech used the term ribozyme (RIE-buh-ZIEM) for an RNA molecule that can act as a catalyst and promote a specific chemical reaction.

Later studies based on Cech's discovery indicated that ribozymes could act as catalysts for their own replication. In fact, self-replicating systems of RNA molecules have been created in the laboratory. These findings support the hypothesis that life could have started with self-replicating molecules of RNA.

Furthermore, other roles for RNA have been discovered. RNA plays a vital role in DNA replication, protein synthesis, and other basic biochemistry. Perhaps most or all of the chemistry and genetics of early cells were based on RNA. This model of the beginnings of life on Earth is sometimes called the RNA world.

Self-replicating RNA molecules might have been not only the first case of heredity but also the first case of competition. For an RNA molecule, self-replication might involve competing with other RNA molecules for a limited number of available nucleotides. A particular RNA molecule with a slightly different structure than other RNA molecules might be more successful in getting nucleotides from its environment and thus more likely to be replicated. Thus, over time, the more-efficient RNA molecules would "survive," and the "world" of RNA would slowly change.

There are several competing hypotheses about how RNA or other simple replicating systems could have evolved into modern cellular life. Some hypotheses propose that certain kinds of minerals formed a template on which organic molecules could line up and form polymers. Another hypothesis is that self-replicating RNA started to evolve inside cell-like structures such as microspheres or coacervates. The self-replicating RNA could have provided the hereditary information that the cell-like structures lack. If the RNA molecules were able to direct the assembly of the structures that carried them, a cell-like system would be formed.

Word Roots and Origins archaea from the Greek archein, meaning "to begin"

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