DNA

Deoxyribonucleic acid (DNA) is the chemical compound which carries the genetic code for all forms of life. It is composed of a series of compounds called nucleotides, linked together in a long chain.

Each nucleotide is made up of a phosphate group, a five carbon sugar (deoxyribose) and a nitrogen containing (nitrogenous) base. There are four types of bases, divided into two groups :

The bases within in the nucleotides bind to each other in a particular manner by hydrogen bonding. Due to the structure of the bases, pyrimidines bind to purines

    ie.    adenine binds to thymine

    guanine binds to cytosine

This binding order allows DNA to rebuild itself from free floating nucleotides, and for single strands of DNA to replicate, forming a complementary strand of DNA from its own template

Each strand of nucleotide bases binds to a complementary strand :

    ie.    AAATGGCCGTTACCT would bind to

        TTTACCGGCAATGGA

The pair of strands then twist around each other, forming a double helix. This helix resembles a twisted ladder, with the base pairs forming the rungs

Since the deoxyribose sugars form the "backbone" of the helix, researchers describe the order in which the base pair sequence is read according to the carbons in the sugar molecule.

ie.    one end is associated with the 5th carbon (5'), while the other end is associated with the 3rd carbon (3')

The two strands of a DNA molecule run in opposite directions : one goes 3'→5', the other 5'→3'

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