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DNA is a long-chain molecule in which the sequence of specific nucleotides determines protein synthesis and hence the structure and function of the entire organism:

The structure of DNA is as follows:

  • it is a double helix molecule formed from two interwoven strands
  • each strand consists of a chain of nucleotides
  • each nucleotide consists of a deoxyribose sugar, a phosphate group and a nitrogenous base
  • there are four possible nitrogenous bases which occur in DNA: adenine (A), thymidine (T), guanine (G), and cytosine (C). Adenine and guanine are purines, whilst thymidine and cytosine are pyrimidines.
  • the deoxyribose sugars make up the backbone of each strand; the nitrogenous bases face each other and are paired by hydrogen bonding. There is specific base pairing:
    • adenine with thymidine, with the formation of two hydrogen bonds
    • guanine with cytosine, with the formation of three hydrogen bonds
  • the deoxyribose sugar backbone of each strand is mediated by the formation of phosphodiester bonds between the phosphate group of one nitrogenous base - itself attached to the 3' carbon of a deoxyribose sugar - and the 5' carbon of deoxyribose on the next nucleotide. The polynucleotide chain that is formed thus has a 5' and a 3' end.

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