Deoxyribonucleic acid (DNA) is a molecule that contains the genetic information to develop and maintain life. DNA consists of four bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These four bases convey huge amounts of information. In the context of DNA, these bases are linked to a sugar (deoxyribose) and a phosphate group to form a nucleotide, the building block of DNA. The human genome has over 3 billion nucleotides.
           The structure of DNA is a double helix; the backbone of the helix is the phosphate and sugar groups with the bases forming the inner rungs. The two strands of the helix are held together by hydrogen bonds between the bases: cytosine specifically bonds with guanine and adenine bonds specifically with thymine. The bonding between the bases is referred to base pairing and the bases are said to be complementary. The bonds between bases are relatively weak, and can be broken (by heat, enzymes, or chemicals) allowing the two DNA strands to separate.

Structure of a nucleotide, the building block of DNA.

The DNA double helix.
The specific base pairing of DNA; Adenine (A) pairs with Thymine (T) and Cytosine (C) bonds with Guanine (G).
Several terms are used when describing our genetic material. Those terms and their relation to each other are described below.
  • Genome refers to all of an organisms' DNA.
  • Chromosomes are long, continuous molecules of DNA wrapped around proteins. Humans have 46 chromosomes and each chromosome contains many genes.
  • Genes are working subunits of DNA that contain the code for a specific product (typically a protein). Genes are arranged linearly along the chromosomes.
  • Nucleotides are the building blocks of DNA