The DNA sequence of some genes contain trinucleotide repeats, like CAG, CAG, CAG. Normally, if a gene has on the order of a dozen repeats, there is not a problem. The expansion of these repeats, however, are associated with several different diseases. The repeats can expand during DNA replication. DNA helicase holds the DNA open, providing access for DNA polymerase to copy the DNA sequence. The trinucleotide repeats can cause the polymerase to slip, making more copies of the repeated sequence and resulting in the formation of a hairpin loop since one DNA sequence is now longer than the other. When the hairpin section goes through a second round of replication, a new elongated complimentary strand is made. These repeat expansions can thus increase with each cell division and over successive generations in a family carrying the repeats.
Trinucleotide Repeat Teaching Tips
The animations in this section have a wide variety of classroom applications. Use the tips below to get started but look for more specific teaching tips in the near future. Please tell us how you are using the animations in your classroom by sending e-mail to firstname.lastname@example.org.
Use the animations to make abstract scientific ideas visible and concrete.
Explain important scientific principles through the animations. For example, the biological clocks animations can be used to demonstrate the fundamentals of transcription and translation.
Make sure that students learn the material by repeating sections of the animations as often as you think necessary to reinforce underlying scientific principles. You can start, restart, and play back sections of the animations.
Urge students to use the animations in accordance with their own learning styles. Students who are more visually oriented can watch the animations first and read the text later, while others might prefer to read the explanations first and then view the graphics.
Incorporate the animations into Web-based learning modules that you create to supplement your classroom curricula.
Encourage students to incorporate the animations into their own Web-based projects.
Trinucleotide Repeat Background
From Lecture Three of the 2003 Holiday Lectures Series "Learning From Patients: The Science of Medicine."