Work record

Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid

James D. Watson and Francis H. C. Crick

1953 · Postwar Contemporary · Essays · English

Copyrightedlow medical relevanceFive-minute digest

Abstract

Written: 1953
Setting: 1951–1953; Cavendish Laboratory, Cambridge, England
Author: James D. Watson and Francis H. C. Crick
Country: United Kingdom
Language: English
Genre: Scientific letter
Form: One-page letter with a diagram
Recommended: Grades 9–12 (One-page technical letter; best read with a diagram.)

Setting. By 1953 experiments suggested that genes were made of DNA, and laboratories in Britain and America were racing to learn its shape from chemistry and X-ray pictures.

Proposal. Two Cambridge researchers proposed that the molecule consists of a pair of spiral strands wound round one axis and running in opposite directions, with sugar and phosphate on the outside and the bases tucked inside.

Pairing. The strands are joined by hydrogen bonds between bases that fit only in fixed partnerships, A with T and G with C, so one strand's sequence fixes the other's.

Evidence. The authors built their model from known chemistry, Chargaff's ratios and X-ray data from King's College London, some of it unpublished and shared without Franklin's knowledge; the letter acknowledges being stimulated by that work.

Implication. A single sentence hints that complementary strands offer a way for hereditary material to copy itself, a point the pair expanded weeks later.

Impact. Printed in the same issue as two King's College papers supplying experimental support, the model founded molecular biology, opened the way to reading the genetic code and led to a Nobel Prize in 1962.

Key figures

James D. Watson: American biologist
Francis Crick: English physicist and biologist
Rosalind Franklin: X-ray crystallographer at King's College London
Maurice Wilkins: Biophysicist at King's College London

Summary

'Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid' is a one-page letter by James Watson and Francis Crick published in the journal Nature on 25 April 1953. In about nine hundred words and one simple diagram it proposed the double-helix structure of DNA, the molecule that carries genetic information in living things. By the early 1950s scientists knew that DNA was made of long chains of sugar and phosphate groups with four kinds of bases attached: adenine, thymine, guanine and cytosine. Experiments had suggested that DNA, rather than protein, carried hereditary information, and the chemist Erwin Chargaff had found that the amounts of adenine and thymine, and of guanine and cytosine, were roughly equal. At King's College London, Maurice Wilkins and Rosalind Franklin were studying DNA by X-ray diffraction, and in California Linus Pauling had proposed a three-chain structure that Watson and Crick believed to be wrong. Watson and Crick built models rather than doing experiments of their own. Their letter describes two helical chains coiled around the same axis and running in opposite directions, with the sugar-phosphate backbones on the outside and the bases on the inside. The chains are held together by hydrogen bonds between pairs of bases, adenine always with thymine and guanine always with cytosine. Because the pairing is specific, the sequence on one chain determines the sequence on the other. The authors noted briefly that this pairing immediately suggests a way the genetic material could be copied, a point they developed in a second paper a month later. The letter acknowledges that the authors were stimulated by the unpublished results and ideas of Wilkins, Franklin and their colleagues. It was printed together with two papers from King's College, one by Franklin and Raymond Gosling, presenting X-ray evidence. The double helix became the foundation of molecular biology, genetics and modern medicine.

Plot or Argument

Rejecting earlier models
The authors explain why the three-chain structure proposed by Pauling and Corey is unsatisfactory.
The double helix
Two right-handed helical chains run in opposite directions around a common axis, with phosphates outside and bases inside.
Base pairing
Adenine pairs with thymine and guanine with cytosine, held by hydrogen bonds.
Fit with evidence
The model is consistent with Chargaff's ratios and with published X-ray data, though not yet proved.
Implication and acknowledgements
The pairing suggests a copying mechanism; the authors acknowledge work at King's College London.

Lessons

Model building
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- How did Watson and Crick arrive at their structure?
- Why was X-ray evidence essential?
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Credit and fairness
Rosalind Franklin's data were shared with Watson and Crick without her knowledge. The story raises questions about honesty and fairness in science.
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- What do scientists owe to colleagues whose work they use?
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- When is understatement more powerful than emphasis?
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Context

After the Second World War, physicists and chemists turned to biological problems. Avery, MacLeod and McCarty (1944) and Hershey and Chase (1952) had pointed to DNA as the genetic material. Several laboratories were racing to determine its structure.

Composition

Watson and Crick built their final model in Cambridge in late February and March 1953, after seeing Franklin's data. Nature published their letter on 25 April 1953 alongside papers by Wilkins, Stokes and Wilson and by Franklin and Gosling.

Reception

The structure was accepted quickly and led to the discovery of the genetic code in the 1960s. Watson's memoir The Double Helix (1968) made the story famous and controversial, especially for its portrayal of Franklin.

Science / Knowledge Technology Modernity Identity Self

Comparisons

Germ Theory Papers (Pasteur and Lister)
Another short scientific publication that changed medicine.
The Internal Secretion of the Pancreas
A laboratory discovery that quickly transformed medical treatment.
Association for Molecular Pathology v. Myriad Genetics, Inc.
The Supreme Court's 2013 ruling on patenting human genes builds on knowledge of DNA.

Quotes

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”

— James D. Watson and Francis H. C. Crick, Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid, Nature 171 (1953), p. 737.

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The Hiding Place, Chapters 3-4
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For Students

A reading companion for classical Christian high school students. See the student guide.

Reading Guide

Watch for

Why the authors reject the three-chain model.
The arrangement of backbones and bases.
The base-pairing rules.
The acknowledgement of King's College work.

Key terms and names

DNA: Deoxyribonucleic acid, the molecule that carries genetic information.
Double helix: Two strands wound around each other in a spiral.
Base pairing: The rule that adenine pairs with thymine and guanine with cytosine.
X-ray diffraction: A method of studying molecular structure from patterns made by X-rays passing through a sample.

Seminar Questions

Comprehension What are the two chains of the double helix made of?
Comprehension Which bases pair with which?
Interpretation Why does specific pairing suggest a copying mechanism?
Interpretation How fairly does the letter credit the King's College scientists?
Interpretation Why might the authors have chosen to state the copying mechanism in a single understated sentence?
Big Question Who deserves credit for a discovery built on several people's work?

Faith Connections

Psalm 139:13–14 (Scripture)
"I am fearfully and wonderfully made": wonder at the making of the human body.
Romans 1:20 (Scripture)
Creation reveals the Creator's power and wisdom.
Darwin, On the Origin of Species (Great Conversation)
Darwin lacked a mechanism of heredity; the double helix supplied one.

Logic and Rhetoric

Central argument: DNA consists of two helical chains held together by specific base pairs, a structure that suggests how genetic material is copied.

Rhetorical device: understatement. The single sentence noting that pairing "suggests a possible copying mechanism" conceals one of the century's great claims.

Debate: Resolved: that Rosalind Franklin should be recognized as a co-discoverer of the structure of DNA.

Writing Prompts

Essay: Explain the double-helix model in your own words and why it mattered.

Comparison with The Internal Secretion of the Pancreas: Compare how teamwork and disputes over credit shaped the discoveries of insulin and the double helix.

Medical Lens

The structure of DNA underlies modern genetics and molecular medicine.

Heredity Degeneration

Creative Prompts

Classroom
Build a paper or bead model of the double helix and label the base pairs.
Essay
Explain why the base-pairing rule suggested a way for genes to be copied.
Dialogue
Write a conversation between Rosalind Franklin and Francis Crick in 1953.