Caption

DNA sample. Researcher looks at a purified sample (white) of Deoxyribonucleic Acid (DNA) in a solution in a test tube during genetic research. DNA encodes the hereditary character- istics of living organisms. The DNA here has been extracted from cells, and will have its structure analysed. DNA consists of huge molecules which are made of two strands that wind around each other in a double helix. The strands each have a sugar- phosphate backbone and are connected by four types of molecular groups known as bases. The exact sequence of bases along the length of the DNA determines the genetic code.