DNA Science: Modeling Rosalind Franklin's Discovery with a Pen Spring
This lesson is the linchpin of our DNA Science eBook. It integrates biology, chemistry, and physics as students follow in the footsteps of pioneering chemical physicist Rosalind Franklin. The lesson was inspired by "How Rosalind Franklin Discovered the Helical Structure of DNA: Experiments in Diffraction", an article in The Physics Teacher journal. High school classrooms, of course, cannot duplicate the x-ray diffraction imaging technique used by Franklin and her team. Instead, they will project light rays from a laser pointer through a ballpoint pen spring to observe and analyze the unique x-shaped pattern produced by a helical structure. They will compare their observations to the pattern in Franklin's famous "Photo 51" image and will use simple geometry to determine pitch angle of their own diffraction patterns.
How Rosalind Franklin Discovered the Helical Structure of DNA: Experiments in Diffraction
This is the article in The Physics Teacher magazine which inspired the creation of this lesson. It was authored by Xavier University Physics Department faculty/staff members Gregory Braun, Dennis Tierney, and Heidrun Schmitzer. It provides in-depth instructions for four classroom activities on diffraction, designed to help teachers integrate biology, chemistry, and physics. The first and second activities are the basis for the expanded lesson and assessment developed by the AAPT's K12 program manager and linked above. The third activity engages students in diffraction calculations using Rosalind Franklin's famous "Photo 51", and the fourth section explains how students or teachers can use mathematical software to generate diffraction patterns produced by a helical spring.