RNA is thought to have been the original
genetic and catalytic molecule for life because it
is capable of storing genetic information like DNA
but is also capable of performing metabolism like
proteins.Needless to say, RNA is not as good as
either in the things that either specializes in,
and as a result, the theory goes, this RNA life
was out-competed by subsequent life that used its
RNA to make proteins to do the metabolism for it,
and then by yet more subsequent life that used
those proteins to make its RNA into DNA as a much
more stable information storage medium.
course, there is the suggestion that proteins
themselves somehow stored information and made the
first RNA, which I think is the other theory that
you are referring to. This "chicken and egg"
question was settled by the observation that RNA
is capable of metabolism as well as information
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