DNA structure

• DNA is a polymer made from four different nucleotides arranged in a repeating fashion
• Each nucleotide consists of alternating sugar and phosphate sections with one of the four different bases attached to the sugar
• There are four different bases in DNA: thymine (T), adenine (A), guanine (G), cytosine (C)
• Chemical cross-links between the two strands in DNA are formed by pairs of bases that always pair up in a specific way, called complementary base pairing
• Complementary base pairing:

  • Thymine pairs with adenine (T-A)
  • Guanine pairs with cytosine (G-C)
• A sequence of three bases in DNA is the code for a particular amino acid, known as a triplet or the triplet code
• The order of the bases in DNA controls the order in which amino acids are assembled to produce a specific protein
• James Watson and Francis Crick worked out the structure of DNA in 1953
• The X-ray crystallography data used by Watson and Crick showed that DNA consists of two strands coiled into a double helix
• Rosalind Franklin and Maurice Wilkins provided data that helped Watson and Crick build a model of DNA
• The famous X-ray diffraction photograph of DNA taken by Rosalind Franklin is known as photograph 51
• DNA structure:

  • The shape of the DNA molecule is a double helix, with two strands twisted together in a spiral