Review: DNA: Secret of Photo 51

Abstract

Photograph 51, originally a NOVA episode, is available as a DVD for classroom viewing. I highly recommend it to high school and college biology, women’s studies, and science history students, as a testament to the sexual discrimination once pervasive in science and still evident in some male-dominated professions. A lesson on DNA would benefit from a showing of this compelling DVD. Students already familiar with the names Franklin, Crick, Watson, and Wilkins who have read Watson’s bestseller The Double Helix may know that Rosalind Franklin, the noir heroine of DNA structure, died at 37. Our textbooks tell us how her discoveries inspired the Watson-Crick model of the structure of DNA, which was awarded the Nobel Prize in 1962. The fact that Franklin’s sine qua non research was not mentioned in Stockholm was not surprising, considering the time in which she lived. The scientists and friends interviewed on the DVD recount with outrage the purloining of her data, vilification of her character, and misrepresentation of her knowledge, the specific details of which may shock viewers whom we teach that science is fair, gender-neutral, and objective, none of which (editorial opinion) it is.Franklin’s intelligence and mastery of subjects is described by two of her public school classmates; says one, “If she understood something she expected to be running it.” As a result of her early research on coal, better gas masks were developed, aiding the war effort. J. T. Randall of King’s College offered her a position in his lab examining the structure of nucleic acids by x-ray crystallography. At that time it wasn’t clear what DNA looked like or how it worked. Her pictures, Photograph 51 among them, were obtained by bombarding DNA crystals with x-rays and collecting with a detector the x-rays diffracted (scattered) by the crystals. These diffraction patterns allow scientists to calculate the three-dimensional forms of complex molecules. Nowadays a computer can analyze diffraction patterns in seconds, but Franklin would have taken an entire year to analyze patterns from a single image, doing a thousand calculations by hand.Franklin’s photos of the “B” form of DNA showed the molecular signature of a helix: the “x” in the center revealed DNA to be a helix with 10 base pairs measuring 34 angstroms per turn; her symmetry data using the “A” form of DNA helped nail down the antiparallel nature of the two strands (the strands run in opposite directions), enabling Crick and Watson to figure out how the bases nestle on the inside of the helix.Franklin’s last work was on the viral structure and infectivity of tobacco mosaic virus and poliovirus. She died of ovarian cancer, having achieved her stated goal of “the improvement of the lot of mankind” in a multiplicity of ways.Science enthusiasts will enjoy the technical details, but our historians and gender-studies students can skip the science-geek bits using the scene selections menu. The DVD can springboard a group or individual activity uncovering other unsung (or sung) heroines of science, past and present. The website (http://www.pbs.org/wgbh/nova/photo51/) produced by WGBH contains inviting animations, photos, and interviews.