DNA has a double helix structure. Each strand is made of subunits called nucleotides.
Each nucleotide is made of a sugar (deoxyribose), a phosphate group, and a nitrogenous base which is
either Adenine (A), Guanine (G), Cytosine (C), or Thymine (T).
The bases form complementary A–T and G–C pairs across the helix.