4. Into which two groups can
the nitrogen-containing bases
that form DNA and RNA be
classified? What is the
criterion used in that
classification?

Gap-fill exercise

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The nitrogen-containing bases that form
and are classified as
pyrimidine and purine bases.

By the analysis of the structural
formulae of those -containing
bases it is possible to realize that three
of them, cy, thy and ura,
have only one nitrogenized ring.
The others, and , have
two associated carbon
rings.