The structure of DNA

• Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions
• The study of chemical, physical structures, and functions of biological macromolecules is known as molecular biology
• Two main classes of nucleic acids

  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)
• DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms and most viruses
• RNA is the genetic material of certain viruses, but it is also found in all living cells where it plays an important role in certain processes such as the making of proteins
• DNA


  A double helix structure consisting of two polynucleotide strands that twine around each other
• DNA


  • Each polynucleotide strand is made up of many nucleotide molecules
  • Each nucleotide in DNA is composed of a five-carbon deoxyribose sugar, a phosphate group, and a nitrogen containing base, all linked together by covalent bonds
• Nitrogenous bases in DNA

  • Purines: Adenine (A), Guanine (G)
  • Pyrimidines: Cytosine (C), Thymine (T)
• DNA strands


  • Form a backbone of alternating phosphate groups and sugars
  • Bases of each nucleotide are attached to each sugar and protrude inward at regular intervals along each strand
  • There is a constant total distance between the sugar-phosphate backbones
  • The two strands are not identical but are complementary to each other, with a purine molecule always paired with a pyrimidine molecule