DNA is found in every cell of our bodies (in at least some stage of its development) and has a beautiful appearance, having the shape of a spiral staircase. The steps (or rungs) are like letters in our alphabet and, ascending or descending the staircase, the letters taken together spell words which have meanings. Altogether, there are around three billion letters in human DNA, which amounts to a lot of information—about a thousand books the size of the Bible. For example, it contains the information needed to grow a baby from a fertilized egg—how to build the heart, lungs, brain and so on. As adults, we need DNA too, as it stores the software that controls much of what goes on inside us.
The sequence of DNA ‘letters’ is like a language, where different combinations of letters have different meanings. Whereas the English alphabet has twenty-six letters, the DNA alphabet has just four: A, C, T and G. Using these four letters, the DNA specifies which amino acid is to be placed in which position along the chain [creation.com]