DNA Structure

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•  DNA is a double helix molecule made of two antiparallel strands of nucleotides linked by hydrogen bonding

   between complementary base pairs

Nucleic acids are composed of nucleotide monomers which are linked into a single strand via condensation reactions

  • The phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’– hydroxyl (-OH) group)
  • This results in a phosphodiester bond forming between the two nucleotides (and water is produced as a by-product)
  • Successive condensation reactions result in the formation of long polynucleotide strands

Two polynucleotide chains of DNA are held together via hydrogen bonding between complementary nitrogenous bases

  • Adenine (A) pairs with Thymine (T) via two hydrogen bonds
  • Guanine (G) pairs with Cytosine (C) via three hydrogen bonds

In order for the bases to be facing each other and thus able to pair, the strands must be running in opposite directions 

  • The two strands of DNA are described as being antiparallel

As the antiparallel chains lengthen, the atoms will organise themselves into the most stable energy configuration  

  • This atomic arrangement results in the double-stranded DNA forming a double helix (~10 – 15 bases per twist)

Organisation of DNA

double stranded DNA