Because it contains the directions for assembling the components of the cell, DNA is often thought of as the "instruction book" for assembling life.

DNA (deoxyribonucleic acid) is the nucleic acid located in the nucleus of a cell. It contains the genetic information that controls all cell activities and has the unique ability to replicate itself. Because it contains the directions for assembling the components of the cell, DNA is often thought of as the "instruction book" for assembling life. DNA is organized into structures called chromosomes. At various points along the molecule, stretches of DNA are grouped into functional regions called genes. Genes can encode for a protein or regulate the expression of other genes. Every cell contains the entire complement of DNA, which, in humans, consists of more than 6 billion base pairs. The chemical structure of DNA was discovered in 1953 by James Watson and Francis Crick. Watson and Crick concluded that DNA is a double helix‚ a twisted ladder, with two phosphate-based backbones and "runged" nucleotides that pair. Attached to the backbone are molecules called nucleotides. Nucleotides attach in pairs (or base pairs), with adenine (A) pairing with thymine (T) and guanine (G) with cytosine (C). The long sequence formed by these four base pairs is, essentially, the genetic code. Shorter sequences of the code are transcribed into RNA, and translated into a sequence of amino acids – the building blocks of proteins.

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