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Chapter 25
Themes
Key
LitCharts assigns a color and icon to each theme in The Double Helix, which you can use to track the themes throughout the work.
Research, Adventure, and the Thrill of Discovery
Scientific Collaboration, Competition, and Community
DNA and the Secret of Life
Academic Life and the University
Summary
Analysis
The next morning, Watson wrote a letter to Max Delbrück, defending his bacteria research and briefly describing the innovative new structure he developed for DNA. But a few minutes after Watson mailed the letter, the crystallographer Jerry Donohue explained that his new DNA structure was all wrong. Watson based his structure on molecular forms in the book The Biochemistry of Nucleic Acids, but Donohue strongly believed that the book listed incorrect forms for guanine and thymine. It put a crucial hydrogen atom in the wrong place. Donohue didn’t have definitive proof, but he was one of the world’s foremost experts on this topic.
Watson quickly regretted mentioning his new theory to Delbrück. He let excitement, pride, and wishful thinking get in the way of rationality and prudence—just like with his and Crick’s first model of DNA. Much like Peter Pauling’s letters from his father, Jerry Donohue’s input on an arcane detail from a biochemistry textbook was a total coincidence, but it also made an essential difference in Crick and Watson’s work. Again, this shows that they never could have succeeded if they hadn’t been surrounded by the right people at the right time—and incredibly lucky.
Themes
Back at his desk, Watson quickly realized that Donohue’s insight made his model impossible. Crick added that, if the two DNA strands had the same sequence, this would make the helix’s angle of rotation impossibly low. Crick also noted that Watson’s model couldn’t explain Erwin Chargaff’s finding that DNA has the same amount of adenine as thymine and guanine as cytosine. After lunch, Watson started avoiding work because he was afraid that he’d never be able to fix his model. Because the shop still hadn’t sent his molecular models for the nitrogenous bases, he spent the afternoon making cardboard versions instead.
Crick and Watson had to discard their second model, even though it was better than their first. They could still learn from their failure. On the plus side, their second model explained how DNA molecules can hold themselves together and replicate, and Crick and Watson could keep these features in their subsequent models. But the second model failed to explain Chargaff’s findings or show how DNA could have a regular molecular structure with an irregular series of bases. Therefore, Crick and Watson needed to focus their energy on those problems.
Themes
In the morning, Watson started experimenting with his cardboard models. He soon realized that adenine and thymine could be linked by a hydrogen bond, as could guanine and cytosine. Moreover, these linked pairs had exactly the same shape. Watson was ecstatic. First, these pairs explained Erwin Chargaff’s findings. Second, they suggested that a two-strand DNA molecule with an irregular series of nitrogenous bases could still have a regularly-shaped backbone. In this structure, adenine and thymine would always bond together, as would guanine and cytosine. Finally, since one chain would be the other’s mirror image, this structure also explained how DNA could replicate itself.
This flash of insight was the key to Crick and Watson’s success. In this passage, Watson describes the double helix model of DNA that students learn about today. But his insight about adenine, thymine, guanine, and cytosine didn’t just provide a viable model of DNA—meaning one that satisfied all the important theoretical requirements and fit with all the available experimental evidence. It also yielded a remarkably elegant model of DNA that clearly revealed its own function. In other words, complementary base pairs weren’t just a good way for DNA to replicate and keep a regular shape with irregular bases—they were the simplest and sturdiest solution that Watson could possibly imagine. So, finding this solution didn’t just crack the code of DNA—it was also a testament to the beauty of nature and the power of science.
Themes
As soon as Crick arrived at the lab, Watson explained his findings. Crick was soon convinced. Although Watson preferred not to reveal their discovery until they were sure, at lunch, Crick told everyone who would listen that they discovered “the secret of life.”
While Watson claims to have reached his pivotal insight alone, he still immediately wanted Crick’s input—after all, Crick had easily pointed out the problems with Watson’s previous models. Convinced that they had the right answer, they struggled to contain their excitement—after all, they fully understood how consequential DNA would be for the future of biology and genetics.
Themes
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