14.1A: Discovery of DNA
- Explain the sequence of events leading up to the discovery of the structure of DNA
What is DNA?
Deoxyribonucleic acid (DNA) is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses.
DNA is a nucleic acid; alongside proteins and carbohydrates, nucleic acids are one of the three major macromolecules essential for all known forms of life. DNA stores biological information and is involved in the expression of traits in all living organisms.
The Path to Discovery
In the 1950s, Francis Crick and James Watson worked together to determine the structure of DNA at the University of Cambridge, England. At the time, other scientists like Linus Pauling and Maurice Wilkins were also actively exploring this field. Pauling had discovered the secondary structure of proteins using X-ray crystallography.
Chargaff’s Rule
Erwin Chargaff met Francis Crick and James D. Watson at Cambridge in 1952, and, despite not getting along with them personally, he explained his findings to them. Chargaff’s Rule showed that in natural DNA, the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units. This strongly hinted towards the base pair makeup of the DNA. Chargaff’s research would help the Watson and Crick laboratory team to deduce the double helical structure of DNA.
Franklin and X-Ray Diffraction
In Wilkins’ lab, researcher Rosalind Franklin used X-ray diffraction methods to understand the structure of DNA. Watson and Crick were able to piece together the puzzle of the DNA molecule on the basis of Franklin’s data, because Crick had also studied X-ray diffraction. In 1962, James Watson, Francis Crick, and Maurice Wilkins were awarded the Nobel Prize in Medicine.
Unfortunately by then, Franklin had died. Nobel prizes are not awarded posthumously, and though her work was crucial to the discovery of DNA, Franklin was never nominated for a Nobel Prize. Francis Crick, James Watson, and Maurice Wilkins were awarded a Nobel Prize for the discovery of the structure of DNA in 1962. There is still much controversy on how her image was given to Watson and Crick and why she was not given due credit.
Key Points
- DNA is one of the most basic molecules of life; it carries genetic instructions for the development, functioning and reproduction of all known living organisms.
- The discovery of DNA’s double-helix structure is largely credited to the scientists Watson and Crick, for which they won a Nobel Prize.
- However, the X-ray crystallography work of Rosalind Franklin and Erwin Chargaff’s work in discovering the composition of DNA were instrumental to the discovery of DNA’s structure.
Key Terms
- double helix : The structure formed by double-stranded molecules of nucleic acids such as DNA.