The structure of DNA, often referred to as the “double helix,” was discovered by James Watson and Francis Crick in 1953. This iconic structure is fundamental to life on Earth. Here’s a breakdown of its key components:


DNA is composed of a series of repeating units called nucleotides. Each nucleotide consists of three parts:

  • Nitrogenous Base: Adenine (A), Thymine (T), Cytosine (C), or Guanine (G).
  • Deoxyribose Sugar: A 5-carbon sugar that forms the backbone of the DNA molecule.
  • Phosphate Group: Attached to the sugar, forming the “phosphate-sugar backbone” of DNA.

Double Helix Structure:

The DNA molecule forms a double helix, where two strands of nucleotides intertwine around each other to create a twisted ladder-like structure. The two strands are held together by hydrogen bonds between the nitrogenous bases.

Base Pairing Rules:

The base pairing rules are critical to maintaining the stability and accuracy of DNA. Adenine (A) always pairs with Thymine (T), while Cytosine (C) always pairs with Guanine (G). This specific pairing is known as complementary base pairing and is crucial for DNA replication and gene expression.

Antiparallel Strands:

The two strands in the double helix are antiparallel, meaning they run in opposite directions. One strand has a 5′ to 3′ orientation, while the other strand has a 3′ to 5′ orientation. This polarity is essential for various biological processes such as DNA replication and transcription.


The structure of DNA is crucial for its ability to store and transmit genetic information. Its stability, precision, and ability to replicate are fundamental to the continuity of life.