The 3-D model of Cytosine (C), Uracil (U), Adenine (A), and Guanine (G), the four nucleotide bases in RNA. Requires the CHIME plug-in to view the models, or they can be viewed statically in .gif format

This site from the Acadia University provides the basic structure of DNA and RNA and a decent compare/contrast between the two.

Purines and pyrimidines are nucleotides. Their properties are described here and their differences are highlighted. Includes examples of each.

A stop codon is a nucleotide triplet in messenger RNA that signals the end of a protein during the translation process. Read about how this works, the different types of stop codons, and how a mutation can sometimes occur.

A start codon is a nucleotide triplet in a genetic sequence that occurs at the start of a protein's synthesis. Read about how this works and how a mutation can sometimes occur.