listen to the audio file and complete the gaps with the following words:
bases, cell, copies, chemical, cytosine, deoxyribonucleic, helix, molecules, nucleotide, sequence, strands, sugar.
Use each word once.

DNA, or acid, is the hereditary material in humans and almost all other organisms. Nearly every in a person’s body has the same DNA.
The information in DNA is stored as a code made up of four bases: adenine (A), guanine (G), (C), and thymine (T). The order, or sequence, of these determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a . Nucleotides are arranged in two long that form a spiral called a double . The structure of the double helix is somewhat like a spiral staircase, with the base pairs forming the steps and the sugar and phosphate forming the vertical sidepieces of the staircase.
An important property of DNA is that it can replicate, or make of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.