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Chapter 17
Themes
and Colors
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
Watson soon got ahold of a powerful new X-ray tube, which let him take pictures much faster. One summer night, he got the picture he wanted: it clearly proved that TMV was a helix. In the morning, Crick confirmed Watson’s finding. Watson was delighted, but he also knew that he wasn’t prepared to study TMV any further.
Watson’s finding demonstrates the psychological rewards of good science: he felt excited by and satisfied with his work. Nevertheless, he still knew that there was another, far more interesting and significant problem out there for him to tackle: DNA.
Active
Themes
Instead, Watson started talking to Crick about the biochemist Erwin Chargaff’s discovery that most DNA tended to have around the same amount of adenine (A) as thymine (T), and the same amount of guanine (G) as cytosine (C). At first, Crick wasn’t interested at all, but he changed his mind when talking with his friend John Griffith, a theoretical chemist. They were discussing the lively debate about whether genes replicate by directly copying themselves, or by creating a complementary surface—a kind of negative image or mold that can then be filled to make more copies of the same gene. Crick and Griffith wondered if they could find an answer by studying bonds. A few days later, Griffith explained that his calculations indicated that adenine and thymine should stick together, as should guanine and cytosine.
Chargaff’s discovery is another example of how DNA science was advancing rapidly while Crick and Watson were busy with other research. The nitrogenous bases adenine, thymine, guanine, and cytosine were significant for Watson and Crick because they were the unique elements in DNA that seemed capable of encoding genetic information. In other words, if scientists could figure out how these four bases worked, they could determine how DNA carried genes. Indeed, readers who are familiar with DNA’s structure and function may immediately understand the significance of Chargaff’s research and Griffith’s calculations. Chargaff’s research suggests that adenine and thymine probably pair together, as do guanine and cytosine. Griffith’s calculations suggest that this pairing is chemically possible. In several chapters, Watson will discover how these pairs encode genes. This also explains how DNA copies itself (although, in reality, it’s through a mix of complementary surfaces and direct replication). The problem of gene replication is significant because, in order for beings to develop from collections of cells into complex organisms with the same genes in every cell, they have to multiply their genetic material somehow. Therefore, a satisfactory model of DNA would have to explain not only what it’s made of but also how it encodes genetic material and replicates itself.
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Themes
Crick and Watson realized that John Griffith’s calculations fit perfectly with Erwin Chargaff’s discovery. However, Griffith wasn’t too confident in his calculations, and Roy Markham believed that Chargaff’s methodology was unreliable. In fact, Chargaff was about to visit Cambridge, so John Kendrew set up a dinner with him, Crick, and Watson. However, Chargaff quickly decided that the disheveled, long-haired Watson was a lunatic, and that the overconfident Crick didn’t know anything about DNA. Crick brought him a copy of Griffith’s calculations the next day.
