Chapter 12, Problem 19STP

Summary Introduction

To explain:

The role that publication of findings had in the discovery of DNA’s structure.

Introduction:

There were many experiments conducted by scientists such as Griffith, Avery, Hershey and Chase, Chargaff and Watson and Crick that led to the discovery of DNA as the genetic material. Many technological developments such as radioactive labeling and X ray diffraction and publication of findings contributed to the scientists’ understanding of the structure of DNA.

Answer to Problem 19STP

The findings of scientists like Hershey and Chase, Wilkins and Rosalind Franklin were published in science journals from time to time. This prompted other scientists to continue with their experiments and provide more evidences to build structure of DNA. Using Chargaff’s and Franklin’s data, Watson and Crick solved the puzzle of the structure of DNA.

Explanation of Solution

In 1952 Hershey and Chase published the results of their experiments that provided definite evidence that DNA is the transforming factor. They used radioactive labeling to trace the fate of DNA and protein as bacteriophages infected bacteria and reproduced. Their experiment provided evidence that DNA, not protein was the genetic material that could be passed from generation to generation in viruses.

Erwin Chargaff analyzed the amount of each nucleotide in the DNA of various species. He published his data in 1950 and found that the amount of guanine is almost equal to the amount of cytosine, and the amount of adenine is equal to the amount of thymine.

Wilkins worked with X ray diffraction at King’s college in London, a technique that involved aiming X rays at DNA molecule. In 1951 when Rosalind Franklin joined King’s college, she used X-ray diffraction technique on the famous Photo 51 and published her data. This data was used by Watson and Crick to solve the structure of DNA. The data indicated that DNA was a double helix formed by two strands of nucleotides twisted around each other.

Using Franklin’s data, Watson and Crick measured the width of the helix and the spacing of the bases. Together they built a model of the double helix that conformed to other scientists’ research. In 1953 Watson and Crick published a letter in the journal Nature that suggested a structure for DNA. In articles individually published in the same issue, Wilkins and Franklin presented evidence that supported the structure proposed by Watson and Crick.