DNA, genes and chromosomes

DNA - deoxyribonucleic acid.  This molecule consists of two long chains of chemicals; nucleotides that twist around each other in a double helix.

• DNA can be copied or 'replicated' - each strand acts as a template for the generation of the complementary strand. 
• Each nucleotide contains one of four nitrogen-containing bases: adenine (A), thymine (T), cytosine (C) and guanine (G). 
• The sequence of these bases constitutes the genetic code - that specifies the order and number of amino acids in a protein.