Rosalind Franklin and the Discovery of the Structure of DNA

Abstract

Issues associated with nature of science (NOS) have long been recognized as an essential component of scientific literacy. While consensus exists regarding the importance of an explicit reflective approach, precisely how to teach NOS remains elusive. The present study explores one particularly promising approach, namely the use of historical narratives. The purpose of the study was to examine whether narratives based on the history of research on the structure of DNA shared using an explicit and reflective approach would affect students’ understandings of NOS. A mixed method approach was used to assess students’ NOS understanding in two different versions of a biology course. In the intervention version, students learned about research on the structure of DNA through historical narratives. In the alternative version, students learned the same material without historical narratives. The Student Understanding of Science and Scientific Inquiry (SUSSI) instrument was administered pre- and post- intervention to all students. Semi-structured interviews with a total of 27 participants from both treatments were conducted to further clarify students’ responses. Results indicate that most of the participants in the intervention treatment made significant changes from pre- to post-assessment in their understanding of two targeted aspects of NOS including scientists’ use of creativity and imagination, and social and cultural influences on science. Female participants in the intervention treatment also stated that learning about Rosalind Franklin’s contributions by way of the story had given them additional confidence to learn science.

Data Availability

The data that support the findings of this study are available on request from the corresponding author, [PD]. The data are not publicly available due to [the privacy/ethical restrictions e.g., their containing information that could compromise the privacy of research participants].

Appendices

Appendix 1

Table 5 Klassen’s (2009) narrative elements, characteristics, and examples included in the intervention treatment

Appendix 2

1.1 Historical Background—Day 1

James Watson was born in Chicago in 1928. He received his bachelor’s degree in zoology from the University of Chicago when he was only 19 years old and received his Ph.D. degree from Indiana University when he was 21 years old. Then Watson was awarded a Postdoctoral Fellowship doing his postdoctoral research at Cavendish Laboratory at Cambridge University in London because he was convinced that DNA was the genetic material. Francis Crick was born in 1916 in England. After he had got his Bachelor of Science degree in physics, he was planning to continue his Ph.D. However, his study was interrupted by World War II. In 1947, Crick was back to school, working on his Ph.D. degree at Cambridge University when he was 31 years old. He also worked in the Cavendish Laboratory (Gibbons 2012).

Around that time, most scientists still believed that compared with the simple molecule DNA, protein should have more possibilities to be responsible for the diversity of life. But some scientists believed that discovering the structure of DNA could help understanding whether DNA is the genetic material. When James Watson and Francis Crick met each other at the Cavendish Laboratory, they found that they had the same interests in discovering the structure of DNA. At the same time, the Cavendish Laboratory at Cambridge University was in a significant competition with the Biophysics Research Laboratory at King’s College in London. Scientists in this lab also believed that DNA was the key to discovering the secret of life and started to transfer their focus from protein to DNA research. This research group used X-ray crystallography to investigate the structure of DNA. This technique can identify the atomic and molecular structure in its crystalline form through the X-rays (Gibbons 2012).

For Watson and Crick, the most likely competitors were Maurice Wilkins and Rosalind Franklin, the British scientists who worked in the Biophysics Research laboratory at King’s College. Wilkins produced the first X-ray clear diffraction images of DNA. And Franklin probably knew the most about the shape of the DNA molecule based on her X-ray diffraction studies. However, the methodological approach used by Franklin and Wilkins was slow. Different from the approach that Wilkins and Franklin used, Watson and Crick did no experiments in the ordinary sense of the word. Instead, they spent their time trying to construct a DNA structural model that made sense and fit the data. Because Wilkins was an old friend of Watson and Crick, they often invited him to come over to talk to them about his DNA research. Wilkins also shared Franklin’s data with them. Therefore, Watson and Crick were familiar with the X-ray information relating to DNA (Maddox 2002).

Based on the information they assembled, Watson and Crick constructed their first DNA model. However, the model was not correct. But Watson and Crick did not give up, and kept thinking about this work. Meanwhile, another potential contender, Linus Pauling got into this competition. He was a famous American chemist and also moved his research into the structure of DNA. His younger son, Peter Pauling, worked in the same laboratory as Watson and Crick. On 28, January 1953, Linus Pauling sent his son a paper in which he proposed the structure of DNA. When Watson and Crick found out about the paper, they were driven by the fear that he would beat them to the structure of DNA. But when they saw the paper, they found Pauling made some similar mistakes on the model just like Watson and Crick had built before. Pauling’s model had a triple-stranded helix with the phosphates at the center and bases on the outside. But they also knew that Pauling would realize his mistakes and make a corrected model very soon. Watson felt that he and Crick needed to speed up to solve the problem (Maddox 2002; Elkin 2003; Gibbons 2012).

When Watson talked with Wilkins about the DNA structure, Wilkins showed him the Photo 51, the clearest picture of B form DNA that Franklin had taken. The amount of tilting and spacing shown on Photo 51 provided the basic parameters of the structure of DNA. It suggested that the molecule was a right-handed double helix. Wilkins and Franklin’s data on the X-ray diffraction of DNA also indicated that the sugar-phosphate backbone of each chain was on the outside of the DNA molecule, and the bases were facing the inside as shown in the Photo 51. Watson and Crick also noted from Franklin’s own notes that the two chains should run in opposite directions. So far, Watson and Crick already got most of the crucial facts to build the DNA model. But they still had one stumbling block in the bases combinations problem. According to Chargaff’s Rules, the amount of adenosine was always equal to the amount of thymidine, and the amount of cytosine was always equal to the amount of guanine. But how could specific pairs of bases (A with T, and G with C) form interchain hydrogen bonds (Maddox 2002)?

Watson tried different bases combinations using cardboards with great creativity. After spending time rearranging the cardboards bases to help him imagine possible structures, Watson finally mated the bases (A pairs with T, G pairs with C) in the double helix. On 28, February 1953, Watson and Crick went to have lunch at Eagle Pub, and Crick told everybody “We had found the secret of life.” Very soon, Watson and Crick published their results in Nature (Watson 2012 [1968]). They proposed that the DNA structure consisted of two antiparallel helical strands; the nitrogenous bases were on the inside of the helix, while the phosphate-sugar structure disposed towards the outside; and most importantly, when the two strands separate apart, each strand of double helix can be used as a template to copy a new strand. This process explained how the genetic material passed from generation to generation (Watson and Crick 1953). At the same time, Wilkins and Franklin also published their results separately to confirm Watson and Crick’s DNA structure (Franklin and Gosling 1953).

In 1962, James Watson, Francis Crick, and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine for their remarkable discovery of the structure of DNA. Rosalind Franklin was not mentioned because she had passed away 4 years ago from ovarian cancer. The Nobel Prize committee rules prohibited the awarding of the prize posthumously (Maddox 2002; Elkin 2003; Gibbons 2012).

1.2 Historical Background—Day 2

Rosalind Franklin was a X-ray crystallographer and chemist who had been working on the structure of complex chemicals in Paris, France. In 1951, known for her expertise in the field of X-ray crystallography, Franklin was offered a fellowship as a DNA researcher in the Biophysics Research Laboratory at the King’s College in London. The other crystallographer, Maurice Wilkins, had been working in that group for several years. He was the assistant director of the biophysics unit and also worked on the X-ray diffraction of DNA. At the time of Franklin’s arrival, Wilkins was on holiday. The head of the Biophysics Research Laboratory called a meeting to introduce Franklin and mentioned that her first task was to adjust the limitations of the laboratory. When Wilkins got back, he found that Franklin had already improved his lab without his permission. Franklin thought she was an independent researcher, but Wilkins thought that Franklin was his assistant. Because of the confusion about who was in charge in the lab, the conflict between Franklin and Wilkins became intense (Glynn 2012).

The situation continued getting worse because of their different personalities. Franklin was articulate, passionate, and good at debate, but Wilkins, on the opposite, was expressionless, shy, and quiet. Wilkins felt it was very hard to communicate with her, and she had a peremptory manner and rebuked him (Maddox 2002). On the other hand, due to the particular cultural environment in London around that time, science was heavily dominated by men, and indeed women scientists were looked down upon. Franklin was in a unique and difficult position as a female pursuing excellence in an overwhelmingly male environment. She felt angry and excluded. She even was not allowed to dine in the same lunchroom with the male scientists at King’s College. Even worse, she was given the sarcastic nickname “Rosy” from her colleagues behind her back (Maddox 2002; Gibbons 2012).

When Wilkins came over to talk with Watson and Crick about his DNA research, he also told them about his tense relationship with a woman scientist named “Rosy” Franklin. He felt that she had shut him out of his research and did not want to share her experimental results with her group. Around that time, Wilkins also passed a lot of information from Franklin to Watson and Crick. Although Franklin was staying in a negative environment at King’s College, she still produced amazing results, including the best X-ray diffraction photos of DNA. She found that DNA has two distinct forms, the A form, and the B form, and there is a transition between them. Besides, she noted that both forms might have helical properties based on her calculation of X-ray diffraction of DNA. In November of 1951, Rosalind Franklin gave a presentation on her startling and revolutionary discovery that DNA’s backbone stands on the outside of the molecule, and its basic structure is helical. Watson attended her talk, but he was not trained in X-ray diffraction and was not able to understand all of the details. Meanwhile, he had a supreme curiosity about the woman scientist “Rosy” mentioned by Wilkins. Watson assessed that Franklin had bad taste in dressing up that went against the standard of feminine beauty (Maddox 2002; Gibbons 2012; Glynn 2012).

Soon after, when Watson returned to his lab in Cambridge, he and Crick built a model of the DNA molecule with its backbone on the inside based on the misunderstanding about what Franklin had presented. When he proudly showed this incorrect model to Franklin, she curtly informed them of their errors. As a result, the meeting turned into an embarrassment for Watson and Crick. When news of Watson and Crick’s failure reached the head of Cavendish Laboratory, he ordered them to leave the study of the structure of DNA to the researchers at King’s College.

Instead of using the speculation that Watson and Crick engaged in, Franklin believed that only the correct data and evidence could prove the structure of DNA. She felt Watson and Crick’s model-building of the DNA molecule was not professional. Franklin was continuously taking X-ray photographs on DNA, collecting the information, calculating the data, and analyzing results. In May 1952, she produced the clearest picture of the B form of DNA. Franklin named it as “photo 51.” The “X”-shaped diffraction pattern crossed over in the center of the photo of B forms of DNA significantly represented a helical structure. Then she put the Photo 51 aside and kept working on the A form pattern. But around this time, Franklin acquired another nickname, “The Dark Lady.” Her unhappiness at King’s College left a legacy of a “face like a thundercloud.” She did not want to keep staying in this unpleasant atmosphere. In early July 1952, Franklin told the leader in the Biophysics Research Laboratory that she was planning to leave King’s College. The personnel committee accepted her resignation, but on the condition, she would finish her analysis of her DNA findings and publish her results. As a result of her decision, Wilkins took over her lab. In the process of the transition, Wilkins obtained the Photo 51 (Maddox 2002; Gibbons 2012).

In January 1953, having kept in touch with Wilkins after the disastrous meeting that revealed their incorrect model, Watson came to King’s College to visit him. At the time, they were feverishly trying to find the structure of DNA before their most famous rival, Linus Pauling (Maddox 2002). When Watson talked with Wilkins about the DNA structure, Wilkins showed Watson the Photo 51, the best picture of B form pattern, that Franklin had taken 8 months earlier. Watson said in The Double Helix “The instant I saw the picture my mouth fell open and my pulse began to race.” It was clear evidence of a helix with its clear “X” in its center and crucial information for Watson to build the DNA model. Watson said in The Double Helix, “Rosy, of course, did not directly give us her data. For that matter, no one at King’s realized they were in our hands race (Watson 2012 [1968]).” Watson drew the pattern of Photo 51 on his newspaper on the train back to Cambridge and prepared to talk with Crick about the significant information. After Crick and Watson had discussed it, they rushed to build the DNA model again.

Watson and Crick were sufficiently convinced that DNA is a double helix with Photo 51. Besides, they also received more valuable information from John Randall, who worked in the medical research council (MRC) committee. He distributed a report describing the most recent work done in the laboratory, which included a summary of Franklin and Gosling’s work about DNA structure. On Franklin’s notebook, a simple drawing illustrated that the two strands of the double helix should run in opposite direction. In other words, one strand ran up and the other strand ran down. Crick immediately realized that DNA had an anti-parallel structure. And in February 1953, Watson and Crick announced their discovery of the structure of DNA. Their model of its structure so perfectly fit the experimental data that it was almost immediately accepted by the scientific community, including Franklin. But at the time Franklin was unaware of the important role her photograph had played in allowing them to build their model (Maddox 2002; Gibbons 2012).

For Watson and Crick, once they discovered the DNA model, they needed to publish quickly. But the problem is that they could not cite Rosalind Franklin’s data because she had not published yet. They also could not refer to the MRC report, which is still officially unpublished. In this event, the heads of Cavendish Laboratory, at Cambridge University, and the head of the Biophysics Research Laboratory at King’s College approached the editors of Nature to agree to publish three articles together. Partly as a consequence of the third placement, Franklin’s paper seemed merely to support Watson and Crick’s work. But her data played far more than just a supporting role. It provided the essential evidence for Watson and Crick to build the correct DNA model (Maddox 2002; Gibbons 2012).

In 1953, Franklin had taken her new position at Birkbeck College. Three year later, she was diagnosed with ovarian cancer. Because working in X-ray labs has some potential risk to people’s health, there is a speculation that the overexposure to X-rays caused her disease. Franklin died in 1958 at the age of 37. In 1962, James Watson, Francis Crick, and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine for their remarkable discovery of the structure of DNA. But the Nobel Committee did not mention Rosalind Franklin’s contributions. Indeed, Franklin’s contributions to Watson and Crick’s discovery did not become widely known until Watson published The Double Helix, by which point Franklin was dead. Thereafter, her role in the discovery of DNA’s structure gradually gained wider recognition, raising questions about whether or not she was properly credited, and Franklin eventually became a symbol of sexism in science (Maddox 2002; Crease 2003; Gibbons 2012; Glynn 2012).

Appendix 3

1.1 Semi-structured Interview Protocol¹

• 1. What is your overall impression of the format of the course?

• Did you enjoy taking a course that featured a “flipped classroom”? Please explain your answer.

• 2. On a regular basis your instructor made a point of raising questions about new material before you viewed the on-line lecture, read the chapter, completed the homework and completed a quiz.

• Was this procedure of raising questions before you had a chance to review the new materials helpful to you or not helpful to you? Why or why not?

• 3. The introduction of new material was often accompanied by the use of pre-assessment instruments, such as surveys and short writing assignments.

• Was the process of coming up with your own answers to questions in a non-evaluative context prior to studying the chapter helpful to you? Why or why not?

• 4. The introduction of new material was also often accompanied by themes or stories from the history of biology.

• Do you think your instructor use the themes or stories to teach in your class? If yes, which approach do you perceive your instructor relied upon to teach?

• What do you mean by themes or stories? Can you give an example of the themes or stories from class?

• Was it helpful to you? Why or why not?

• 5. In your opinion, would it be helpful or unhelpful for your instructor to use stories in class?

• What do you see as the advantages or disadvantages of using stories in science classes?

• 6. Did the way your instructor introduced course content by means of broad themes and/or stories give you any insights into the practice of science?

• Please explain your answer with an example.

• 7. Did the way your instructor introduced course content by means of broad themes and/or stories help you understand the content of the course?

• Please explain your answer with an example.

• 8. Did the way your instructor introduced course content by means of broad themes and/or stories make you more or less comfortable learning science?

• Please explain your answer with an example.

Possible prompts

• Could you expand on that?

• Could you tell me more about that?

Next go over differences in student responses to the Pre and Post SUSSI.

• 9. I’d like to ask you some questions about a specific class devoted to the discovery of the structure of DNA. Can you tell me what you thought about this particular class?

• Did your instructor introduce the process of discovering the structure of DNA? If so, how did your instructor introduce this topic?

• Was it helpful for you to learn the content? Why or why not?

• Was it by themes or stories?

• What do you mean by “themes”/ “stories”?

10. Does the process of science involve creativity and/or imagination?

• What do creativity and imagination in science mean to you?

• If yes, explain and provide examples. If no, explain why not.

• Did what you learned about the discovery of the structure of DNA help you learn how creativity and imagination are involved in science? Explain.

11. Does the process of science involve social and cultural factors?

• What do social and cultural factors mean to you?

• Is science affected by society and/or cultural factors? If yes, explain and provide examples. If no, explain why not.

• Is science today affected by social and cultural factors? Why or why not? If yes, explain and provide examples. If no, explain why not.

• Did what you learned about the discovery of the structure of DNA help you learn how social and cultural factors are involved in science?

• In your opinion, do you think men and women are treated equally in current society?

13. Do you think there are any connections between the class questions and activities for the discovery of the structure of DNA and the assessment we just discussed? If so, what connections do you see?

¹The questions in the interview script are based on ideas from Norris et al. (2005). A Theoretical framework for narrative explanation in science. Science Education 89(4): 535–554.

Appendix 4

Table 6 SUSSI Likert items comprising NOS components developed from Liang et al. (2008)