How does DNA work?

DNA is an ideal molecule to transfer genetic messages to every cell of your body. When an egg and sperm met to form the first cell that was to become you, you were given the complete genetic code that all of your cells will use for the rest of your life.

In that first cell, half of the chromosomes (half of the DNA molecules) came from your father and the other half came from your mother.

The first cell divided to become two cells, these both divided to become four, then eight then 16 and so on. Some of the cells in your body are still dividing, for example to produce new skin or blood cells. Most of the time a cell divides perfectly and each of the DNA molecules is copied exactly, with one copy going to each of the new cells. If mistakes are made, they are fixed or the cell is marked for destruction.

If a problem occurs in this process the new cells often die, but on rare occasions the faulty cells survive and can cause a wide range of problems. However, sometimes these faults (mutations) can be beneficial for the organism: this is the basis for evolution.

In order to make a copy of itself, the DNA molecule unzips lengthwise, leaving unpaired bases along each backbone. Nucleotides, which are made up of a sugar, a phosphate and one of the four bases, float freely in the nucleus. Because A can only pair with T and G can only pair with C, the nucleotides match up with the unpaired bases along the DNA backbone. Like building blocks, they form a new strand that is complementary to (matching) the sequence. This forms strands identical to the original strand before it unzipped.