The Double Helix

Teacher’s notes

LEVEL 6

PENGUIN READERS Teacher Support Programme

The Double Helix James D. Watson

Advances in understanding DNA were being made across the Atlantic by a brilliant American scientist, Linus Pauling. Watson and Crick know that time is short and that they are in a race with Pauling to find the structure of DNA. The middle section of the book deals with their attempt to understand DNA by using models. They can’t persuade any other scientists that theirs is the right way, however, and after a failed first attempt, their work on DNA stops. Having upset all the people who could have helped them, it seems that Crick and Watson will never make it. Life at Cambridge continues and Watson has plenty to say about accommodation and meals in Cambridge colleges.

About the author

In the final part of the book, the race to unravel DNA gets hotter. Linus Pauling at Cal Tech in Pasadena, California, is nearly there. He publishes a paper, but too soon. Watson and Crick immediately realize that he has made a fundamental error. Their desire to win the race sends them running back to their DNA ideas and models. Watson recounts how they arrive at the answer, finally winning the support of their colleagues as they get there.

James Watson was born in 1928 in Chicago in the United States. He studied first at the University of Chicago and then took his PhD at the University of Indiana, winning his doctorate when he was still only twenty-two. The story of his career from 1950 to 1953 and the discovery of the double helix are told in this book. After receiving the Nobel Prize in 1962, Watson moved from Cambridge to Cal Tech in California where he worked until 1968. The second volume of his autobiography, Genes, Girls and Gamow, was published in 2001 and talks in detail about these years. It also deals with his bumpy love life, ending with his marriage to his present wife, Liz.

Summary James Watson’s account of how he and fellow scientist Francis Crick discovered the structure of DNA is a famous piece of popular science writing. There is as much about the personalities of the scientists involved in the momentous race that finally identified the double helix as there is about proteins and crystallography. Non-scientists can enjoy his story of human achievement and weakness as much as readers with a science background. The events of the story take place over only three years, from 1950 to 1953. It begins in the cold north of Copenhagen, with Watson’s arrival in Europe in search of a career. Various branches of science failed to interest him and he is quite honest about his unfocused early working life. Knowing that his real interest lay in understanding genes, he moved to Cambridge University in England, where he immediately teamed up with the excitable Francis Crick. Crick’s loud voice gave many of his colleagues a continuous headache. c Pearson Education Limited 2008

The story ends with Watson, aged only twenty-five, and Crick, announcing to the world that they have uncovered the nature of life. Chapters 1–2: Watson introduced the main characters in the story. These include Francis Crick, who will later becomes his colleague, Max Perutz, who runs the unit where Crick works, and Sir Lawrence Bragg the director of the Cavendish Laboratory. Maurice Wilkins works in London with his assistant Rosalind Franklin. Linus Pauling is working on the structure of DNA at Cal Tec in California. Watson explains that as a student he didn’t study areas of science that did not interest him. Now he needed this knowledge to do his research with DNA. He worked in Copenhagen with biochemist Herman Kalckar, who sent him to an animal study centre in Naples, Italy. There he attended a meeting and saw for the first time, an X-ray diffraction picture of DNA by Maurice Wilkins. He tried, but failed to make friends with Wilkins. Whilst on a trip to Geneva, he learns that Linus Pauling has shown a model of the alpha helix, which he thinks is part of the structure of DNA. Chapters 3– 4: Rosy Franklin wanted Maurice to stop taking X-ray photos of DNA. Rosy was refusing to share her results with Maurice until she gave a talk three weeks later. Bragg threatened not to give Crick a research place at the Cavendish after he completed his PhD. Max Perutz The Double Helix - Teacher’s notes

of 5

Teacher’s notes

LEVEL 6


The Double Helix and John Kendrew defended Crick. Bragg accepted that he and Crick had had the same ideas independently but he still did not like Crick personally and hated his endless chatter. Crystallographer V Vand suggested a theory for the diffraction of X-rays by helical structures. Crick quickly saw Vand’s theory was not valid but tried to find a more accurate theory. He talked to Bill Cochran the cleverest of the younger Cambridge X-ray people. The next day, Crick told John and Max about his ideas. Bill Cochran also thought Crick was right, but found a shorter, more elegant mathematical system. They checked their ideas by looking again at X-ray diagrams. The agreement was so good that both the Linus model and the Cochran-Crick theory had to be correct. They wrote a paper and sent it to Nature with a copy to Linus Pauling for his comments. Chapters 5–6: Rosy gave a talk on her results but delivered it poorly. She thought X-rays were the only way to find structure of DNA and playing with models was a waste of time. Watson travelled to Oxford with Francis Crick who asked about Rosy’s talk. Watson had not taken notes and could not say how much water was in the DNA. Crick showed that only a small number of structures were possible with Rosy’s pictures and Cochran/Crick mathematics. Crick thought one week of playing with models would bring the answer. At the same time there was competition between different teams in the United Kingdom and the United States. In the UK, there was also competition between teams in Cambridge, Oxford and London. Watson and Crick knew they needed different models. A three-chain helix seemed good and fitted with Rosy’s talk. Crick phoned Maurice Wilkins to check with him. They planned to give a presentation to Maurice. Firstly, Crick would present helical theory, then Watson and Crick would explain how they developed their model. On the day of the presentation Maurice said helical theory was not new. Rosy was impatient and said there was no evidence that DNA was helical. She became aggressive when they presented a three-chain model. Watson had not remembered the amount of water correctly. After this Bragg told Watson and Crick to stop work on DNA. Model work could be done at King’s London. Crick said the Alpha Helix was part of a larger helix. The ban on working on DNA did not stop them from thinking about it. c Pearson Education Limited 2008

Chapters 7–8: Watson received a letter from Washington saying he was sacked but also offering money to work on TMV. Watson read about earlier research on TMV by Bernal, Fankucken and Schramm. He showed an X-ray picture of TMV to Crick who saw helical structures. Hugh Huxley taught Watson how to use the X-ray camera. They heard news that Pauling was coming to London but the US State Department had revoked his passport because of his political opinions. Salvador Luria also could not get a passport so Watson had to describe the American work to a meeting in Oxford. Al Hershey had said that the key feature of viral infection of bacteria was injection of viral DNA – a powerful new proof that DNA is the primary genetic material. Rosy was saying her DNA was not a helix. Watson used a new powerful X-ray tube to take photos of TMX. He took a picture that showed a helical structure. He showed it to Crick who saw the helix immediately. It was now clear no more benefits would come from studying TMV. Austrian chemist Erwin Chargaff at Columbia University had studied DNA, in particular their purine A and G bases and their pyramidine C and T bases. Chargaff could not explain why some life forms had more A and T while others had more C and G but thought it was significant. Francis and chemist John Griffith discussed different systems of gene copying. Some thought genes split in two, others thoughts they joined like pieces of a jigsaw puzzle. Chargaff came to Cambridge but he was not impressed by Crick and Watson. Chapters 9–10: Watson met Max Delbruck from Cal Tech. Watson showed a TMV picture to Delbruck but it did not convince him. Linus Pauling arrived. His talk only restates his published ideas. Two weeks later, Watson met Pauling in Royaumont. They talked about Watson doing X-ray work with viruses in Pasadena. Linus Pauling’s wife Ava Helen said her son Peter was coming to Cambridge next year to work with John Kendrew. She asked Watson to help him settle in Cambridge. Watson started to be interested in sex between bacteria. Cavalli-Sforza and Bill Hayes had discovered that bacteria were male or female. Joshua Lederberg had proved they showed genetic recombination. Lederberg thought each contributed equal amounts of genetic material, but Bill Hayes believed the amounts were not equal. Watson read Lederberg’s papers. Francis Crick and Maurice talked about Rosy’s lack of cooperation. Crick forgot to tell Maurice about the agreement between Griffith’s calculations and Chargaff ’s data. The Double Helix - Teacher’s notes of 5

Teacher’s notes

LEVEL 6


The Double Helix Peter Pauling arrived in Cambridge saying his dad is interested in coiling of alpha helices in hair protein. Crick worked on coiled coils, with the help of Kriesel, they found the correct figures and wrote a paper for Nature before Pauling. Francis Crick planned to go to Brooklyn for a year. There were more problems between Rosy Franklin and Maurice. Watson was now at Clare College but hated the boring English food. He had stomach pains and went to the doctor but got little help. Odile and Crick helped him to find better place to live and eat. Peter Pauling got a letter from his dad saying he had a structure for DNA. Chapters 11–12: Two copies of Pauling’s paper arrived, one for Bragg, and one for Peter Pauling. Watson and Crick studied Peter’s copy. Pauling described a three-chain helix with a sugar phosphate backbone at centre. Watson saw it was wrong but did not know why. Pauling’s nucleic acid was not an acid at all. Watson told Roy Markham who confirmed that the chemistry was crazy. Crick and Watson knew they had about six weeks to find the answer. Rosy rejected Pauling’s idea because it was a helix. There was almost a fight between Watson and Rosy. Maurice said they had found new form of DNA called the ‘B’ structure. Watson saw the pattern was unbelievably simpler. An X-ray showed a helix clearly. R D B Fraser had tried to make three-chain model for the structure without success. Watson tried to find a two-chain structure. Watson described the B form to Bragg and Max Perutz. He wanted the Cavendish to make models. Bragg encouraged him. Watson worked on a two-chain model with the backbone at the centre, then a model with the backbone outside. Watson tried to study the chemistry of bases. Were there two chains with bases held together by hydrogen bonds between the same types of bases? The essential trick of gene copying could come from the requirement that each base in a newly produced chain always bonded through hydrogen to a similar base. Chapters 13–15: American crystallographer Jerry Donohue said Watson had chosen the wrong physical forms of G and T bases. Francis Crick also saw problems. Watson realized that A bonds to T and G bonds to C. This type of double helix suggested a much better form of copying. They needed to make a model to check if these ideas were correct. But before they had checked, Francis rushed into the pub saying they had found the secret of life.

c Pearson Education Limited 2008

Gradually they improved the model and showed it to more colleagues. They discussed how to release the news. Watson thought about how to phrase the letters he would need to write. Bragg saw the model in the afternoon. Bragg could see the logic of the model but was worried about not checking with Alexander Todd. Maurice saw the model and immediately liked it. He said he would return to London to check the model with his X-ray pictures. Two days later he phoned to say that he and Rosy found the X-ray data matched the model. They were writing up their results and wanted to publish at the same time as Watson and Crick. Todd came to look at the model, he congratulated them on their work. Pauling heard about the double helix from Delbruck. Pauling was excited but wanted to see the X-ray evidence from King’s College. Watson and Crick started to draft their paper for Nature. Crick added a sentence saying that the pairing they had described suggested a possible copying system for genetic material. Bragg saw the paper and said he would send to Nature. Linus Pauling came to Cambridge to see his son Peter and also to see the model. He said Watson and Crick had found the answer. Watson went to Paris with his sister and Peter Pauling to celebrate Watson’s twenty-fifth birthday.

Background and themes The illustration on the front cover is of a double helix – the structure of a DNA molecule. A helix is a spiral. A double helix consists of two parallel spirals. Nature of scientific discovery: One of the major themes of The Double Helix is the nature of scientific discovery. Scientists start with complex evidence and they search for simple explanations. Watson and Crick were searching for a simple explanation for very complex evidence. Scientific specialization: Scientists often specialize in a small area of study. In The Double Helix, Crick and Watson’s search for a simple explanation of DNA is made more difficult by the poor communication between these specialist groups. Women in science: Watson paints a very negative picture of fellow scientist, Rosalind Franklin, a woman alone in a man’s world. In their Nobel lectures, Crick and Watson did not even acknowledge her contribution to their success. In the years before her death, both Watson and Crick got to know Rosalind Franklin better, and saw her as the hard-working and successful scientist that she was.

The Double Helix - Teacher’s notes

of 5

Teacher’s notes

LEVEL 6


The Double Helix Discussion activities

1 Group work: Find out how much students know about DNA and the discovery of its structure. Encourage students to share their knowledge in groups. Finally collect feedback from groups as a whole class activity.

9 Write and role play: Prepare a conversation between Francis Crick and his wife Odile. Francis wants to talk about his discoveries about Vand’s theories. Odile wants to decide what to wear when they go out to the Green Door. When you have done this, act out your conversation. 10 Discuss: Crick says that Bill Cochran’s mathematical system was shorter and ‘more elegant’ than his own. Discuss the meaning of ‘elegant’ in this context.

Chapters 1–2, pages 1–16 Before reading

Chapters 5–6, pages 30–45 After reading

Introduction Before reading

2 Discuss: Talk about what Britain was like in 1950. Remember it was a few years after the end of the Second World War. What did towns look like? What did people wear? What did they eat? What did they do for entertainment?

After reading 3 Role play and group work: Make seven cards with the names James Watson, Francis Crick, Max Perutz, Sir Lawrence Bragg, Maurice Wilkins, Rosalind Franklin and Linus Pauling. Have students choose a card from the pack and introduce themselves to the group saying what they do, where they work and who they work with. Students must try to answer any questions from the group. Tell students to use the information from the Introduction and Chapters 1–2. 4 Research and group work: Working in groups prepare a two-minute presentation on the Alpha Helix using the information in the book and from research from other books or the Internet. Let each group present to the whole class and choose the best presentation. Discuss why it was the best.

Chapters 3–4, pages 16–30 After reading 5 Role play: Have students work in pairs. Student A: You are James Watson, a young American man of twenty-three. You are going to meet Sir Lawrence Bragg one of the greatest scientists in Britain. Greet Sir Lawrence politely and introduce yourself. Answer any questions he asks you about your life and work. Student B: You are Sir Lawrence Bragg. Greet James Watson and ask him questions about his life and work. 6 Role play: You are James Watson’s landlady. Complain to him about the noise he makes when he comes in late. 7 Role play: Act out the meeting between Sir Lawrence Bragg and Francis Crick in Sir Lawrence’s office described on page 26. 8 Write: Write a letter from Rosalind Franklin to Maurice Wilkins saying why you don’t want to share the results of your latest work. Explain that you need these for the talk you will give in three weeks from now. c Pearson Education Limited 2008

11 Write: Imagine that Watson writes an informal letter to Crick describing Rosy’s talk. Use the information contained in their reported conversation on the train on pages 31–34. 12 Role play: Choose to be James Watson or Rosalind Franklin. You are being interviewed on breakfast TV (so not too scientific!). Say why your method of study of DNA structure is the best method. Say why the other methods are useless.

Chapters 7–8, pages 45–57 After reading 13 Role play: You are a Cambridge friend of James Watson. He calls you from Scotland on 2 January. Ask him about his Christmas holiday in Scotland and if he has enjoyed it. 14 Write: Write the letter that Watson receives from Washington. Use the information on pages 47 and 48. 15 Write: Prepare the short report on developments in the United States that Watson gives in Oxford. Apologize for the fact that Pauling and Luria are not present and explain why. Use the information in Al Hershey’s letter. 16 Present: Deliver the short talk you prepared in activity 15. Answer as many questions as you can.

Chapters 9–10, pages 58–68 After reading 17 Role play: Have students act out the scene between Ava Helen Pauling and James Watson. Collect the information you need from page 59. 18 Write: Share ideas and then write a letter to Peter Pauling telling him a little about Cambridge. Mention the beautiful buildings, the cold weather, the cold houses and the horrible food. Tell Peter that you know John Kendrew and that will do everything you can to help him to survive his time in Cambridge. Use the information in both Chapter 9 and Chapter 10. Remember to describe Cambridge from an American point of view. 19 Role play: Role play the scene with the hostess at the garden party on page 60. 20 Discuss: How do you feel about the way Watson writes about Rosy on page 64? Is he justified or is he unfair? Imagine, what Rosy would say about her position if she was writing this book? The Double Helix - Teacher’s notes

of 5

Teacher’s notes


LEVEL 6

The Double Helix 21 Role play: Have students act out the scene of Watson’s visit to the doctor on page 65.

Chapters 11–12, pages 68–85 After reading 22 Role play: Act out the scene in Maurice Wilkins’ office when Rosy tells him she wants to transfer back to Bernal’s laboratory at Birkbeck College. Use the information on pages 68 and 69. 23 Write and discuss: Describe the contents of Linus Pauling’s paper and what you (James Watson) think is wrong with it. Use the information on page 70. 24 Discuss: Linus Pauling sent two typed copies of his paper: one to Lawrence Bragg and the other to his son, Peter. This was in the days before photocopiers and email. How would the story have been different if all the characters had had access to these modern technologies.

Chapters 13–15, pages 85–102 After reading 25 Role play: James Watson is working with a model of DNA when Francis Crick comes into the lab. James tells him about his idea about pairing A and T held together with two hydrogen bonds and G and C held together with two hydrogen bonds. James explains the advantages, mentioning that this structure could explain a much better copying scheme (see page 89). 26 Role play: Student A is Watson. Student B is Crick. Have students work in pairs and act out the scene between Watson and Crick at the pub on page 91. 27 Role play: Have students work in pairs and role play the scene in which James Watson explains that the typist at the Cavendish laboratory was not available, and he asks his sister Elizabeth to type the 900-word article. The students can take turns playing the role of Watson.

Extra activities 28 Group work: Invite different groups of students to research, using libraries and the Internet, either Charles Darwin, Carl Linnaeus or Gregor Mendel. Consider the life, ideas and achievements of each and how this relates to the work of Crick and Watson. Each group should prepare and deliver a short presentation to the class on the selected scientist. After the last presentation, the significance of these individuals can be discussed in class. 29 Research: Find out more about Sir Lawrence Bragg and his work in X-ray crystallography for which he was awarded with the Nobel Prize in Physics in 1915. Why did this make him a very suitable person to lead the team searching for the structure of DNA? 30 Discuss: On 26 June 2000, after ten years’ international cooperation between scientists from Europe, Japan, Britain and America, the first draft of the genetic sequence of a typical human being was announced by the Prime Minister of Britain and the c Pearson Education Limited 2008

President of the United States. The sequence is called the human genome and opens up endless possibilities. Genes that carry inherited diseases, for example, may be isolated and removed from a parent’s sperm or egg. In the future parents may be able to design their own children. Are these developments good ideas or are they a dangerous interference with nature? 31 Discuss: Genetic engineering is the deliberate alteration of the DNA of an organism in order to change its character. This is already practised in many areas, using DNA from one species to change another. Genes from a fish that lives in very cold water, for example, have been introduced into the DNA of a tomato, so that the tomato can survive much colder temperatures. Tomato growers will then be able to extend their growing season and make more money. Genes from a jellyfish have been introduced into pigs. The piglets resulting from this cross had bright yellow snouts and trotters, glowing in the dark as jellyfish glow underwater. The point of this exercise was to prove that modified genes could be used to grow human organs, which could then be used in transplant operations. Once again, are these positive scientific developments, or are they a dangerous interference with nature? 32 Artwork: On page 17, Watson describes a walk along the river through King’s and Trinity colleges saying: I had never seen such beautiful buildings in all my life. Use books and the Internet to find photographs of the beautiful buildings in Cambridge. Make a display with notes for other students in your school. 33 Research and write: In 1962 John Watson, Francis Crick and Maurice Wilkins were jointly awarded with the Nobel Prize for Physiology or Medicine. Find out more about Alfred Nobel and the Nobel Prize. Learn more about winners of the Nobel Prize. 34 Research and write: Lawrence Bragg was born in Australia in 1890. When he was five years old, he fell off his tricycle and broke his arm. His father, a great scientist William Henry Bragg had heard about the work of Röntgen’s experiments with the newly discovered X-rays. His father used X-ray’s to examine his son’s arm (the first time this had been done in Australia). Find out about Röntgen and his discoveries. Have you ever had an X-ray? Tell your friends about it. 35 Debate: Write this statement on the board: ‘Genetic engineering is a good thing for the future of the world.’ Take a class vote. Divide the class in two. One half prepares arguments in favour, the other against. There are some ideas in the Background and Themes section above. Students present their arguments and ask each other questions. Take a second class vote. Has anyone changed their mind?

Vocabulary activities For the Word List and vocabulary activities, go to www.penguinreaders.com. The Double Helix - Teacher’s notes of 5