Chapter 12, Problem 9A

Summary Introduction

To summarize:

The experiments and data shown in the given photo that led to the discovery of DNA.

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 also contributed to the scientists’ understanding of the structure of DNA.

Answer to Problem 9A

An important experiment was done by Rosalind Franklin in 1952 when she photographed her fifty first X ray diffraction pattern of DNA. Famously known as photo 51, it revealed a lot of information about the structure of DNA. This photo was later used by Watson and Crick to develop the double helical structure of DNA molecule.

Explanation of Solution

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 to photograph DNA. This given photograph became the famous Photo 51. When analyzed and measured carefully, the pattern shows the characteristics of double helix structure. Her 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.