MODEL RELEASED. Teenager demonstrating DNA replication. Teenage boy at home demonstrating the replication of the double helix of DNA (deoxyribonucleic acid). This macromolecule, found in cell nuclei, comprises two sugar phosphate strands in a twisting helical shape. These strands (black and white) have nucleotide bases (coloured) that bond to each other and join the two strands together. The sequence of bases forms the genetic code. Before replication, the strands separate from each other (centre). Each strand then each acts as a template for the formation of two new DNA molecules (bottom). This is known as semi-conservative replication.