With their discovery of the structure of DNA Watson and Crick started the unravelling of the mystery around this molecule. But after that the questions started rising: how was the DNA able to copy itself with every cell division? And how did the DNA eventually lead to genetic properties? The copying When a cell divides, the two strands of DNA are seperated. The bonds between the basepairs are broken, forming a sort of zipper. After seperation the two strands exist with single bases. Then the copying starts. On the opposite of each A in the strand a T is built in the new strand, on the opposite of a G a C is built in. The missing strand is built again from single nucleotides, so a copy is made. This is also done for the other strand. In the picture the pink strand is the old strand and the blue one the new strand. Eventually two double stranded DNA molecules exist. These are seperated from each other during cell division, so each cell gets its own molecule. The genetic code DNA codes for genetic properties in our body by the unique sequence of the bases. To express these properties the nucleotide sequence must be translated into proteins. Proteins consist of a sequence of specific building blocks. these building blocks are called amino acids.   [1]  [2]