In 1953, James Watson and Francis Crick proposed that DNA has a double helix structure. This model describes DNA as two long strands of nucleotides that twist around each other, resembling a ladder that has been twisted. The “rungs” of this ladder are formed by specific pairing of nitrogenous bases, with adenine (A) always pairing with thymine (T), and guanine (G) always pairing with cytosine (C).
Double Helix:
DNA is composed of two strands that coil around each other to form a helix, which is also referred to as a double helix.
Nucleotides:
Each strand of DNA is made up of repeating units called nucleotides.
Base Pairing:
The two strands are held together by hydrogen bonds between specific pairs of nitrogenous bases: adenine (A) and thymine (T), and guanine (G) and cytosine (C).
Sugar-Phosphate Backbone:
The “rails” of the ladder are formed by a backbone of alternating sugar (deoxyribose) and phosphate groups.
Complementary Strands:
The base sequence of one strand determines the base sequence of the opposite strand, making them complementary to each other.