Students will explore the methods scientists used to determine the structure of DNA. By using the story of how Watson and Crick determined the structure of the DNA molecule, students can see the process of trial and error in science. They can also better understand why it is important to have all of the facts before model building begins. Students make a model using the method that Watson and Crick used to make their first DNA with disastrous results. Then they determine their amount of experimental error after measuring their model and comparing it with Franklin and Wilkins' data. This is day one of a three day lesson. Here is an overview of what students will learn today.
Using the Frayer method, students should define double helix.
Students will be viewing selected clips from the BBC movie Life Story that outlines the discovery of the structure of DNA. (Note: In America, it can also be found under the name, The Race for the Double Helix.) (Part 1 can be found here and part 2 can be found here.) In today's lesson, the clips focus on the work of Watson and Crick. Show students the following clips, pausing after each clip to give them time to complete the graphic organizer on page 1 of the student handout. Students will glean information from the clips about what was known about the structure of DNA using the graphic organizer from the student handout. They will also give a short synopsis of each clip.
Clip 1 (Introductions): 12:02-13:57
Clip 2 (The goal):16:00-17:27
Clip 3 (Gossip): 18:41-19:09
Clip 4 (Form A): 22:41-23:07, 34:04-36:40
Clip 5 (Early model building): 37:56-39:00
After viewing all the clips, explain to students that they will building a model of DNA using equipment found at their lab table. As they are building the model, they should keep in mind the data that was mentioned in the video clips.
After student watch the video clips, they should build a model of DNA that best represents what they have in their notes. They are able to use anything provided on the lab table. Also provide copies of certain scientific papers that Watson and Crick would have had on hand (e.g.: Astbury, Pauling, Chargraff). Once students have completed their model. They should photograph it with a metric ruler in the frame for scale. They should also record the dimensions of their model on the student handout. Here is a student work sample of a completed model.
Explain to students that once they finish their first model, Watson and Crick asked the team from Oxford to come for a viewing. Show students a clip from the Double Helix to see how the first Watson and Crick model was received by Franklin, Wilkins, and the rest of the team from Oxford by viewing the clip from 40:08-41:47.
When the clip is complete, ask students how their model would compare to the information that Franklin revealed in the clip. Have them pair with their partner and discuss particular flaws that their models might contain. Students should make a list of those flaws on the student handout (or in their lab notebook). They should be prepared to share their ideas with the rest of the class.
Explain to students how to calculate experimental error by comparing the actual data collected by Rosalind Franklin with the dimensions of their model. They should record their calculations on the student handout or in their lab notebook.
Using part of the data provided by Rosalind Franklin in the video clip, students will rotate around the world and critique the model of their peers. Students should use this rubric in their critique.
Once students have had a chance to critique two other models, have the students discuss of the importance of model building and obtaining all the scientific data known about the topic of DNA before the model was built.