The Structure And Composition of DNA

Outline the structure and composition of DNA

Deoxyribonucleic acid (DNA)

  • A form of nucleic acid which are made up of its building blocks called nucleotides covalently linked together by 3’,5’- phosphodiester linkages
  • In DNA, the nucleotides are composed of an aldopentose (2-deoxyribose) bonded to a phosphate group and linked to a heterocyclic purine and pyrimidine bases (nitrogenous bases)


    • Adenine (A)
    • Guanine (G)


      • Cytosine (C)
      • Thymine (T)

Structure of DNA

      • Primary Structure
        • consist of alternating sugar-phosphate backbone with different nitrogenous bases attached onto it
        • Its individual nucleotides are connected via a phosphate ester linkage between the 5’-phosphate group on one nucleotide residue and the 3’-hydroxyl on the sugar of another nucleotide residue

        • Secondary Structure
          • consist of two polynucleotide strands coiled around each other in a double helix
          • The two antiparallel strands which are held together by hydrogen bonds pairs are complementary due to specific base pairing

Chargaff’s rule

          • %A = %T
          • %C = %G