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.

Diagram of DNA showing the bonding between the corresponding bases e.g. adenine (A) to thymine (T) and guanine (G) to cytosine ©