I. Curricular Framework

Concept:

Models

Essential Question:

What are the greater implications and/or consequences of the study of the DNA scientific model?

Bridge:

Specialization

Content:

The DNA Model: Structure Determines Function

Outcomes:

II. Standards Aligned

III. Instruction and Assessment

1. Connect: Connecting to the Concept Experientially

Objective: To have students experience a common example of a model by actually building a model paper airplane and paying attention to how its structure affects its flying pattern.

Activity: Teamed with a partner, the students are given a piece of scrap xerox paper, a piece of good colored xerox paper, and a set of directions for making a paper airplane. Without explanation, they are instructed to read the directions to teach themselves to make the airplane and then to make their own, good model. This takes approximately twenty minutes. Of course they may practice to make sure it flies. There are many books available in libraries and book stores which contain a wide variety of paper planes which, because of their structural features, perform different stunts. It's preferable to give each team a different flyer to produce. This adds to the fun and lays the groundwork for the idea that structure determines function. The teacher can then take ten to fifteen minutes to have a contest where each team comes up, describes the plane's structural features, and what trick they hope it will perform. One set of directions follows at the end of the cycle.

Assessment: Quality of student interest, participation and model planes.

2. Attend: Attending to the Connection

Objective: To have students analyze what a model is, what are some different kinds of models, and why models are useful.

Activity: After the contest, the teacher can lead the class in an analysis of the experience. Some questions which may be discussion starters are included at the end of the cycle. Obviously, they center around the nature of a model, what a model is, and why models are useful. The students can also be encouraged to share other models with which they are familiar.

Assessment: Quality of discussion and students' ability to express the purpose of models.

Assessment, Phase One, Level of Engagement, Fascination:

3. Image: Creating a Mental Picture

Objective: To have the students move from the general idea of a model to the special use of models in science by showing a video that shares several specific examples of scientific models.

Activity: To make the bridge to scientific models, specifically that of Watson and Crick's DNA model, the students are shown the Search for Solutions segment on Modeling. This segment is one of nine, twenty minute segments which are readily available on a free-loan basis and may be copied by the school. In this segment on Modeling, several examples both historical and current are shown. One of these features, Linus Pauling, and how he made a paper model of the alpha helix while recovering from a cold. Oodles of noodles (found in the supermarket and very inexpensive) can be brought in their package--tightly coiled to fit. Then boil them right before their very eyes. They relax and you can start to spread them out a strand at a time to show that chromatin, about a meter of it, must be VERY tightly coiled to fit inside the nucleus of a cell.

Assessment: Student attention and response to the video.

Assessment, Phase Two, Seeing the Big Picture:

4. Inform: Receiving Facts & Knowledge

Objective: To give the students the basic features of DNA as explained by Watson and Crick's model and to show how those structures explain its role in replication and protein synthesis by lecturing and critical questioning.

Activity: The teacher presents the classical, structural features of Watson and Crick's model of DNA. The important underlying concept is Structure determines Function. This critical information lays the foundation for an understanding of replication, protein synthesis and genetic engineering. While the purpose of this octant is to provide the learner with the facts, this does not mean that many visual means are not employed to make those facts as clear as possible. Demonstrations are particularly helpful in a topic that is abstract. A little egg white in a beaker, mixed with a bit of rubbing alcohol and stirred with a glass rod is also an excellent simulation of what extracted DNA looks like. Pop beads and a long zipper are also invaluable when teaching DNA and its functions.

Assessment: A short test on the material presented.

Assessment, Phase Three, Success with Acquiring Knowledge:

5. Practice: Developing Skills

Objective: To make sure students not only know the facts about DNA structure, but to see if they can use that information by using paper and computer problem simulations related to DNA replication and protein synthesis.

Activity: In this octant, the students work as a class on a computer program called The Master Molecule. The menu for this program provides choices which allow the review of DNA structure, replication and finally introduces mRNA, tRNA and ribosomes and their roles in protein synthesis. By using a large screen TV monitor and gathering the whole class around this proves to be an enjoyable activity that is confirming for the students and their confidence in the material. This can be followed up with a paper/pencil assignment for class or for homework that involves transcription and translation and results in the primary structure of a piece of imaginary protein. A copy of the worksheet follows at the end of the cycle.

Assessment: Student participation and quality of answers in the computer simulation and then successful completion of the worksheet.

Assessment, Phase Four, Success with Acquiring Skills:

6. Extend: Extending Learning to the Outside World

Objective: To have the students now build their own model of DNA which will allow them to visualize the helical formation and the way its structure permits replication and then how it serves as a template for mRNA in protein synthesis.

Activity: Just about every lab manual or teacher reference book has directions for students to build paper models of the nucleotide parts which can be assembled into a model of DNA. There are also some inexpensive, completely re-useable plastic kits for DNA/RNA modeling which have the advantage of twisting and showing a three-dimensional representation. It is also fun, and a bit more creative to let the students decide what material they'd like to use to make their model. Different kinds of candy has been a favored choice. They can use five different kinds of candy to represent each of the nitrogen bases, another type for the sugars and another for the phosphates. Gum drops work well!

Assessment: Quality of the model in its representation of the facts.

7. Refine: Refining the Extension

Objective: To begin to have students explore some of the current research being done which requires the understanding of the molecule called DNA.

Activity: Students do some out of class research on topics such as amniocentesis, cloning genetic engineering and genetic counseling. A possibility for this last section which serves as a very good lead in to a next chapter on DNA research today is to have a guest speaker come in who is a technician with an expertise in karyotyping. The guest could explain the purpose and procedure and show some real examples.

Assessment: Quality of discussion.

8. Perform: Creative Manifestation of Material Learned

Objective: To have students explore current techniques and research being done which is built on the foundations of the material they have just studied.

Activity: There are a number of lab manuals which provide very realistic chromosome pictures which carry different abnormalities. The students can do a karyotype themselves by cutting and pasting, identify the genetic abnormality which they have found to be present, and then do some research on that disease, its severity and consequences, and share that in an oral report to the class.

Assessment: Quality of the karyotype, proper identification of the chromosomal abnormality and resulting syndrome, research and class presentation.

Assessment, Phase Five,Performance, Creative Use of Material Learned: