DNA is the genetic information which is passed on from one generation to the next. DNA is condensed into chromosomes prior to DNA replication and cell division. If humans we inherit 23 chromosomes from our mother and 23 chromosomes from our father giving our somatic cells 46 chromosomes. DNA is found in the nucleus of cells. DNA can also be found in the mitochondria of all cells ad the chloroplast of plant cells. Different organisms have a different number of chromosomes in the nucleus.
DNA is made up of nucleotides. A nucleotide contains a sugar (deoxyribose), a phosphate and a nitrogenous base. There are four different bases that make up DNA; Adenine, Thymine, Guanine and Cytosine. DNA is double stranded and takes on the shape of a twisted ladder or double helix. The backbone of the double helix consists of the repeating phosphate and sugar molecules. The steps or rungs of the DNA ladder (double helix) are complementary base pairs. Adenine and Thymine are complements and Guanine and Cytosine are complements so they generally pair together.