Section 19.3 DNA Is the Hereditary Material

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1 Provide coloured paper or blocks. Have the students manipulate the paper or blocks to visualize the gene locations. ASSESSMENT Assessment Opportunities (Evidence) Assessment Categories Knowledge STS Skills Practice question * (Student Book page 639) q. 1 Lab Exercise 19.B: Mapping Chromosomes * (Student Book pages ) Section 19.2 Questions (Student Book page 641) q. 1, 2 30 C2.3k q. 3 * For Attitude Outcomes refer to Attitude Outcomes in the Unit 30 C Curriculum Correlation chart on page 582. For ICT Outcomes refer to the ICT Outcomes Correlation chart on page 585. Section 19.3 DNA Is the Hereditary Material BACKGROUND INFORMATION Sir Isaac Newton once said, If I have seen farther than others, it is because I was standing on the shoulders of giants. In 1882, chromosomes were discovered. Seventy years later, the molecular structure of this macromolecule was discovered. Each researcher added to the knowledge of those who came before. Although it has been described as a race to find the answer, the discovery of DNA s structure combined the research of many scientists from many countries. This research philosophy set the stage for the most recent advance in the science of molecular biology, the mapping of the human genome. There has been much discussion about government control of research through funding, and many people believe that politics has a strong, and sometimes negative, effect on what gets studied in science. Possibly bowing to pressure from religious groups, many regions in the United States are banning stem cell research. Prerequisite Knowledge and Skills have basic biochemical knowledge about atoms, molecules, types of inter- and intramolecular bonds, and the main groups of macromolecules: carbohydrates, lipids, proteins, and nucleic acids recognize the historical and social context in which early discoveries of biochemistry were made, particularly in terms of how they affected (for good or ill) the advance of scientific understanding understand the basic principles of experimental design and the fair test have a basic understanding of radioactivity and its usefulness in monitoring different compounds in biological systems Misconceptions Students often picture the stereotypical scientist, working alone in his (it is a stereotype, after all) lab until the final eureka moment when he reveals the truth to the waiting masses (à la Dr. Frankenstein). Modern science thrives on publication and peer review. Copyright 2007 Thomson Nelson Unit 30 C Cell Division, Genetics and Molecular Biology 675

2 Research details appear in scientific journals, to be re-tested by others or to inspire new experiments. Modern scientists do not work in a vacuum but are in contact with others; professional dialogue is encouraged and, in fact, vital. The final research that produced the presently accepted model of DNA was conducted by three men and one woman, one from the United States and three from Great Britain; a molecular biologist, a physicist, a biophysicist, and another molecular biologist specializing in X-ray crystallography. Related Resources Nelson Biology Alberta Solutions Manual Nelson Biology Alberta Student CD Nelson Biology Alberta Computerized Assessment Bank Safety in the Science Classroom, Kindergarten to Grade Alberta Education. Instructional Strategies and Assessment Tools Assessment Rubric 1: Knowledge Assessment Rubric 2: Inquiry Assessment Rubric 3: Communication Assessment Rubric 4: Making STS Connections Assessment Rubric 6: Research Skills Diagnostic Assessment Master 1: Understanding Key Concepts Self-Assessment Checklist 1: Inquiry Skills Self-Assessment Checklist 2: Research Skills Tracking Sheet: Inquiry Skills Nelson Biology Alberta Lab and Study Masters LSM 19.3A Student Worksheet Investigation 19.2: Isolation and Quantification of DNA DNA Structure Molecular Model Kit, Science Kit and Boreal Laboratories (item # ) TEACHING STRATEGIES Planning Narrative/Practice 80 min Lab Exercise 19.C: Evidence of Hereditary Material 40 min Web Activity: Canadian Achievers Avery and MacLeod 10 min Web Activity: Simulation Elementary, My Dear Crick 10 min Investigation 19.2: Isolation and Quantification of DNA 200 min (see below for details) Explore an Issue: Competition and Collaboration Advance Science 40 min Section 19.3 Questions 15 min There is a link to visual support on the Nelson Web site wherever a video icon appears in the Student Book. 676 Unit 30 C Cell Division, Genetics and Molecular Biology Copyright 2007 Thomson Nelson

3 Have the students work in small, student-directed groups to create a timeline from 1869 to This should be drawn to scale to highlight the rate of progress as information accumulated. For each date, the groups should briefly summarize the discovery and (most importantly) show how it built on a previous discovery (or discoveries). By following this process, students will better appreciate the cumulative nature of scientific knowledge. The teacher s role is as a support or as a guide to assist groups that lose sight of their goal. The timeline falls into two sections, divided by Lab Exercise 19.C. Hammerling s work led to nuclear research; Griffith s work restarted the progress after his accidental discovery. If students show interest, direct them to the Quirks and Quarks audio clip on current gene research, found on page 658. Technology and ICT Integration Collaboration in science goes on today. You might refer students to the Web sites of some refereed scientific journals, for example, Biochemistry and Cell Biology, Nature, and The New England Journal of Medicine, to give them an idea of one way in which scientists communicate with one another. INVESTIGATION/ACTIVITY SUPPORT Lab Exercise 19.C: Evidence of Hereditary Material (Student Book pages ) 40 min The Griffith experiment is an example of how scientific discoveries (sometimes) favour the inquisitive mind. Griffith was attempting to develop a vaccine for pneumonia. When he observed the transformation of non-pathogenic bacteria into disease-causing ones, he did not abandon his experiment because it didn t do what he had hoped; he published his findings. The follow-up research of Avery, McCarty, and MacLeod led scientists to abandon the study of chromosomal proteins and focus on the nucleic acid. Although students cannot experiment with pathogenic bacteria, the data provided allow them to recreate the analysis that Griffith applied to his data. Students may need to refer to a chart or other visual showing the treatment each mouse received and the result that was observed. Consider posting one on the board. Be sure that students understand the answers to the Analysis and Evaluation questions before they move on to the Synthesis questions. This could be done by having students discuss their answers in small groups and then compare them as a class. For Synthesis (i), students could work in pairs. Assign each pair one of the protocols and have them present their hypotheses to the class. Copyright 2007 Thomson Nelson Unit 30 C Cell Division, Genetics and Molecular Biology 677

4 Web Activity: Canadian Achievers Avery and MacLeod (Student Book page 646) 10 min The development of the DNA model was an international effort. This Web activity highlights the Canadian contribution by showing the role of Avery and MacLeod in the process. This activity should be performed after the students have added Avery, MacLeod, and McCarty to their timeline. It provides an opportunity for students to test their connection of one discovery to another. Pre-lab Discussions Have the students rate the importance of Avery and MacLeod s work. Would they consider it the most significant piece of evidence so far? (Note that there is no right answer to this question. It asks students to look at the big picture.) Post-lab Discussions Ask students, before they continue their timelines, to predict where the research will go next. Web Activity: Simulation Elementary, My Dear Crick (Student Book page 651) 10 min Erwin Chargaff was a biochemist working at Columbia University. He shared a critical piece of evidence when he visited Watson and Crick at Cambridge in Watson and Crick borrowed from his work but gave him little credit. Pre-lab Discussions Have the students rate the importance of Watson and Crick s work. Would they consider it the most significant piece of evidence so far? (Note that there is no right answer to this question. It asks students to look at the big picture.) Students should access this Web Activity before adding the work of Watson and Crick to their timelines. Post-lab Discussions Ask students, before they continue their timelines, to predict where the research will go next. Investigation 19.2: Isolation and Quantification of DNA (Student Book pages ) 200 min (if all parts are completed), 160 min (if parts 3 and 4 are omitted), or 80 min (if either animal or plant DNA is isolated) 678 Unit 30 C Cell Division, Genetics and Molecular Biology Copyright 2007 Thomson Nelson

5 Even the most modern of genetic research must start by isolating DNA. Students often wonder why liver and onions are used. Aside from the obvious joke potential (as in We re having liver and onions in the lab today ), any plant or animals could be used; all living things contain DNA. These are inexpensive and available and not likely to cause problems of an ethical or allergic nature. The first step is to break down cell walls and membranes. Grinding with salt is used in this experiment; some versions of the experiment use a detergent solution. DNA is insoluble in cold ethanol, which is less dense than aqueous solutions; if poured carefully, a layer of DNA will precipitate at the interface. None of the other cell components will be in this layer. Diphenylamine reacts with adenine and guanine (purines that are the basis of DNA), forming a blue complex. Because it contains glacial acetic acid, it may not be permitted in the school; the teacher should check the school board s policy before purchasing this compound. Without teaching the complexities of spectroscopy, students should at least be told that different molecules absorb light at different wavelengths so that the more of the molecule that is present, the greater the amount of solar energy that will be absorbed. A known sample of DNA can be used to determine the amount of DNA isolated; there should be no other substances in the isolate. Many schools will not have a spectrophotometer, making this step impossible. Teacher Preparation The ethanol must be cold; overnight storage in the freezer will yield better results. Part 3 of the procedure requires a fume hood. Pre-lab Discussions To be sure that the process is understood, give a pre-lab quiz. The procedure is very detailed, and good technique is essential to success. Walk the students through the procedure, demonstrating the techniques. (This does not suggest that this is a teacher demonstration; the experiment is within the ability of students.) Some of the chemicals used (ethanol and diphenylamine) are potentially dangerous. When demonstrating, wear the same protective equipment as the students. Part 3 should be performed in a fume hood under close teacher supervision. Post-lab Discussions Have students compare the results of the two isolations. Extensions/Modifications Any biological sample may be used; kiwi fruit is a better-smelling alternative to onions. The Internet offers variations of methods that could be performed and compared. If time is an issue, divide the class in half. Provide onions to one group of students and liver to the other; the results can be pooled and compared. Copyright 2007 Thomson Nelson Unit 30 C Cell Division, Genetics and Molecular Biology 679

6 Materials/Equipment safety goggles rubber gloves fresh beef liver scissors mortar and pestle 0.9 % (w/v) solution of sodium chloride (NaCl) three 10 ml graduated cylinders sand (very fine, washed) cheesecloth two 50 ml beakers or two large test tubes 10 % (w/v) solution of sodium dodecyl sulfate (SDS) 95 % ethanol (chilled) 50 ml graduated cylinder glass rod four medium test tubes 4 % (w/v) solution of sodium chloride (NaCl) onion blender (optional) hot-water bath boiling chips ice-water bath meat tenderizer solution (3 g/50 ml of solution) diphenylamine solution 25 ml graduated cylinder Safety and Disposal Diphenylamine should always be used under a fume hood. If diphenylamine is spilled, instruct students to hold the affected part under running water for 15 min. Any surface should be rinsed with running water. Part III deals with a potentially corrosive agent. It is important to ensure that students wear gloves and goggles during this activity. Before disposing of any chemicals, check the local regulations for disposal of hazardous materials. Explore an Issue: Competition and Collaboration Advance Science (Student Book page 650) 40 min The theme of Section 19.3 has been the collaboration of modern scientists to achieve a goal. This activity allows students to investigate the reality. In times of war, scientists often work in isolation. The English during World War II did not want their enemies to know about RADAR, so experiments were not published. During America s Manhattan Project, scientists were not even allowed to talk with researchers at the same lab until they convinced the military that security was preventing progress. 680 Unit 30 C Cell Division, Genetics and Molecular Biology Copyright 2007 Thomson Nelson

7 Have the students work in groups. Extensions/Modifications Hold a formal debate on the proposition Scientific progress is driven by competition, not collaboration. ASSESSMENT Assessment Opportunities (Evidence) Lab Exercise 19.C: Evidence of Hereditary Material (Student Book pages ) Web Activity: Canadian Achievers Avery and MacLeod * (Student Book page 646) Web Activity: Simulation Elementary, My Dear Crick * (Student Book page 649) Assessment Categories Knowledge STS Skills Investigation 19.2: Isolation and Quantification of DNA * (Student Book pages ) Explore an Issue: Competition and Collaboration Advance Science * (Student Book page 650) Section 19.3 Questions (Student Book page 651) q C3.2sts q C3.1sts 30 C3.1s 30 C3.2s 30 C2.4s * For Attitude Outcomes refer to Attitude Outcomes in the Unit 30 C Curriculum Correlation chart on page 582. For ICT Outcomes refer to the ICT Outcomes Correlation chart on page 585. Copyright 2007 Thomson Nelson Unit 30 C Cell Division, Genetics and Molecular Biology 681