Station 5

Station 5: History of DNA discovery

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DNA Day: Discovery of the Double Helix —

The Discoverers of the Structure of DNA

• DNA is a molecule found in every cell of your body, and it’s what makes you unique! DNA stands for “deoxyribonucleic acid.” It decides things like your hair color and height, and it also has instructions for your body to make proteins it needs to work. Even though DNA is famous for its shape, we didn’t know what it looked like until the 1950s.

• DNA was first found in 1869 by a scientist named Friedrich Miescher. He was trying to get a type of protein from white blood cells but found a different molecule instead. He called it “nuclein.”

Nucleotides and Their Bases

• Many scientists worked to figure out what “nuclein,” now called DNA, was made of. They found out that DNA has parts called nucleotides. Nucleotides are made of a sugar, a phosphate group, and one of four bases: Adenine (A), Thymine (T), Guanine (G), or Cytosine (C). These bases are in two groups: pyrimidines (C and T) with one ring, and purines (A and G) with two rings. Nucleotides link together by the sugar of one base connecting to the phosphate group of the next base, making the “sugar-phosphate backbone.”

Rosalind Franklin and X-ray Diffraction

• Even though scientists knew what DNA was made of, they didn’t know how it fit together in 3D. Rosalind Franklin, an English chemist, worked on DNA’s structure. She used x-ray crystallography, a method where x-rays are aimed at a crystal form of a molecule, and the pattern they make helps experts understand the molecule’s structure. Franklin’s images of DNA were given to two other scientists, James Watson and Francis Crick, without her knowing, by her boss Maurice Wilkins.

The Three-Dimensional Structure of DNA

• Watson and Crick were also studying DNA’s structure. They didn’t do experiments themselves but used other scientists’ findings. They weren’t the only ones trying to figure it out. Scientists Pauling and Corey suggested a different model with three strands. With Franklin’s images, Watson and Crick found out DNA had a helical shape. They used a new way of building models to show that bases fit together perfectly (A with T and C with G), held by hydrogen bonds. They proposed a model of DNA that we still use today. It has a sugar-phosphate backbone on the outside and paired bases on the inside.

• In 1962, Watson, Crick, and Wilkins won the Nobel Prize in Medicine for their work on DNA’s structure. Many people think Rosalind Franklin should have won too, but she had died in 1958, and the prize can’t be given after death. She didn’t get much credit back then, but now people are working to recognize her contributions.

• The discovery of DNA’s structure helped us understand genetics and biology better. It even led to the creation of the COVID-19 mRNA vaccine.