Structure of DNA

Genetic information is passed from one generation to the next. This is called heredity and why we resemble our parents. The genetic information itself is contained in a complex molecule called DNA .

Scientists worked out the structure of DNA in the 1950s. Rosalind Franklin made ‘X-ray diffraction’ images of DNA. James Watson and Francis Crick used information from one of her images to work out a model for the structure of DNA. Work by Maurice Wilkins, a colleague of Franklin, supported their model.

X-ray diffraction photograph of DNA
An X-ray diffraction image of DNA

Watson and Crick were able to work out how DNA was arranged and the tiny distances between its different features. They worked out that in a DNA molecule:

  • there are two strands
  • the strands are twisted around each other to form a double helix
  • the strands are held together by bonds between base pairs
Nucleotides join together to form twisted strands around each other to form a double helixA DNA molecule showing its base pairs, G–C and A–T

Watson, Crick and Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine for their discovery. Franklin had died before then and so could not be awarded it with them.