Crick, Watson, and Franklin 5

Home , Francis Crick, Maurice Wilkins, Rosalind Franklin, The Double Helix

CRICK, WATSON, AND FRANKLIN

BIOGRAPHY

740L CRICK, WATSON, AND FRANKLIN

THE RACE TO DISCOVER THE STRUCTURE OF DNA

Born Born July 25, 1920 June 8, 1916 London Northampton, England James Watson

Died BornDied DiedBorn April 16, 1958 FebruaryJuly 28, 2004 12, 1809 April 19,6, 1928 1882 ByLondon Lorem Ipsum Shrewsbury,San Diego, California England Downe,Chicago, England Illinois By Cynthia Stokes Brown, adapted by Newsela In 1953, three biochemists helped unlock the mystery of life. They had determined the structure of the DNA molecule. Found in all life on Earth, DNA contains the information that allows organisms to regrow cells and pass on traits to offspring.

2 3 Setting the Stage

Darwin explained natural selection and evolution. But he didn’t know how traits were passed down. Traits are handed down from parent to child, through generations. Over time, some traits change. Slight changes in traits as they get passed down are what makes evolution possible.

This process was still not well understood a whole century after Darwin. Then after World War II, scientists began to study biology in a new way.

In the 1950s, biochemists realized that DNA contained the instructions for copying a new organism. A yard of DNA (deoxyribonucleic acid) is folded. It is packed into the nucleus of every cell in pairs called “chromosomes.”

DNA has three parts:

1. a type of sugar called “ribose”

2. a phosphate responsible for its acidity

3. four kinds of bases — adenine (A), thymine (T), guanine (G), and cytosine (C)

These four bases seemed too simple. How could they pass on all the information needed to create a new organism? The key was that the bases combine in different patterns to mark different genetic traits.

Scientists wondered how to study the DNA molecule. Biochemists wanted to understand its structure. Then they could understand how a new organism is copied. They began taking X-ray images of crystals of DNA.

Linus Pauling worked at the California Institute of Technology. He was a pioneer in “X-ray crystallography.” Pauling seemed likely to unlock the mystery of life. He had already concluded that the general shape of DNA must be a helix, or spiral.

4 5 The race

The competition to unravel DNA was one of the great scientific races of all time. Victory went to three people working in England. The first was Rosalind Franklin. She worked at the University of London. The other two were James Watson and Francis Crick. They worked together at Cambridge University, just 50 miles away from Franklin.

Franklin was from London. She earned a PhD from Cambridge in chemistry. While studying DNA, she became an expert in X-ray crystallography. She was able to produce clear and accurate images of DNA crystals using precise X-ray equipment and pure DNA samples.

At Cambridge, Francis Crick was 35. He was working on his PhD in the crystallography of proteins. He grew up in a small English village.

Watson was only 23 in 1951. He grew up in Chicago. He entered the University of Chicago at age 15, and got his doctorate from the University of Indiana at just 22. He was at Cambridge to learn crystallography.

Using her precise X-ray images, Franklin began to make hypotheses about the structure of DNA. In late 1952, she took an especially clear X-ray image. Her colleague Maurice Wilkins showed the image to Watson. He did so without telling Franklin or asking her permission.

When Watson saw the image, he knew at once that DNA had to be a helix, or spiral. He returned to his lab to begin making models out of metal and wire. Watson and Crick built models to try to visualize DNA. How many strands did the helix have? Which direction did the strands run? Were they on the inside or the outside? How were the four chemical bases arranged?

Franklin believed better quality X-ray images would solve the problem. But Watson and Crick knew they were racing against Pauling. They felt making models would lead them to an answer quickly. Using paper models, Crick and Watson finally visualized a structure that solved the puzzle. They pictured DNA like steps on two spiral staircases. The bases bonded together in pairs. Rosalind Franklin working at King’s College in London

6 7 The news gets out

Crick and Watson published their discovery in Nature magazine in April 1953. Wilkins and Franklin wrote articles to go along with it.

In 1962, Wilkins, Watson, and Crick received the Nobel Prize for their work. Franklin could not share in the prize. She had died in 1958 of cancer. She was just 37. Exposure to X-rays may have contributed to Franklin’s death.

Even if she had lived, she may not have shared in the prize. Crick and Watson never told Franklin they used her images. They didn’t give her much credit in their Nature article. Much later, Watson admitted that they could not have solved the problem without Franklin’s work.

Watson and Crick also addressed how DNA copies itself. They proposed that DNA’s double helix unzips into two strands to make a copy. Each strand has a backbone of sugar-phosphates with the four bases attached.

Crick continued his research in England until 1976, when he moved to California. He died there in 2004. Watson returned to the United States. He did research at Harvard from 1956 to 1976. He helped establish the Human James Watson and Francis Crick in 1959 Genome Project in the early 1990s. He retired in 2007.

They made up the steps in the staircase. The ribose sugar made up the sides, or railings, of the stairs.

The two men made this discovery in February 1953. Sitting at lunch in their usual pub, they announced that they had found the secret of life.

8 9 Sources Image credits

Bryson, Bill. A Short History of Nearly Everything, 398–415. New York: Francis Crick in 1962 Broadway, 2003. © Bettmann/CORBIS

James Watson Judson, Horace Freeland. The Eighth Day of Creation: Makers of the © Bettmann/CORBIS Revolution in Biology. New York: Simon and Schuster, 2003. Rosalind Franklin Maddox, Brenda. Rosalind Franklin: The Dark Lady of DNA. New York: © Science Source Harper Collins, 2002. An illustration of the DNA double helix © the Big History Project Watson, James D. The Double Helix: A Personal Account of the Discovery of the Structure of DNA. New York: Atheneum, 1968. Rosalind Franklin working at King’s College in London © Science Source Watson, James D. and Francis Crick. “A Structure for Deoxyribose James Watson and Francis Crick in 1959 Nucleic Acid.” Nature. April 25, 1953, vol. 171. Annotated version available © Bettmann/CORBIS at http://www.exploratorium.edu/origins/coldspring/ideas/printit.html

Wilkins, Maurice. The Third Man of the Double Helix: The Autobiography of Maurice Wilkins. Oxford: Oxford University Press, 2003.

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