pull tight. You've made the first rung. Be sure that the "u-wire's" ends are even.
- Step 6: Pull the ends of the bases wire into the center of the ladder and thread two more bases onto one side of the bases wire and take the other bases wire and thread through the two just-threaded bases to make rung at a right angle to the uprights. *** Important!! The bases wires go through each other in opposite directions.*** (These additional complementary bases can be either the same or different colors from the first two sets of bases you used, depending on your personal preference.)
- Step 7: Continue threading the bases wire up through the next sugar and phosphate on each "upright". Now add two additional complementary bases to the bases wire as you did in Step 6. (At the end of this activity, you will use whatever combination of bases you decided on to determine the amino acids coded for in your model.) Thread the bases wire through the next sugar and phosphate set, and add another base pair.
- Steps 5-7 repeat!!
Basic pattern is:
Up two on both sides
Add two in the middle
Cross through the two in the middle
Up the next two on both sides.
And again, and again, and again...
- Step 8: Repeat steps 6 and 7 until you have attached alternating base pairs to each sugar and phosphate set of the "uprights". You should do at least thirteen base pairs to have a large enough molecule to twist.
- Step 9: Twist all of the wires at the top of the ladder together. You can twist and cut closely or finish with one last pony-bead or E-bead around the point where the wires form the model and the keychain or earring holder connect. If the molecule is loose, untwist the bottom two wires and gently pull on each . This will tighten the sides and make the bases perpendicular to the sides. Retwist together and trim after tightening. (Not too tight because you still need to twist into a double helix!)
- Step 10: Twist your model into the Double Helix, and tape it onto the accompanying worksheet. Make sure you tape the model so that the top of it corresponds to the order of the colors listed in your color key.
- Step 11: Then complete Part 2 of your model and decode your model. The jewelry you created will be yours to keep and wear/use after you have handed in this completed worksheet and your teacher has corrected it.
NOTE: Provided you have the optional materials needed, you can also use this pattern to make necklaces, bracelets, tie clips, or other pieces of DNA jewelry. To make larger models, start with two lengths of wire for the sugars-phosphates strands approximately double the desired length of the finished piece of jewelry. String the beads as directed, (Steps 1-9). Hint: Thread the bases in sections--18" of wire in the u-shape for base threading is manageable. Finish off the necklace or bracelet with a barrel clasp, a keychain, or earring wires, as directed in Step 9. Some students might want to make the standard two inch DNA model and use cording to finish into a necklace or bracelet.
Part 2 - Decoding your Model:
|DNA Jewelry Model:||by:______________|
|A =||(Tape here. Make sure that|
|T =||the top corresponds to|
|C =||your color key.)|
(Color code a diagram below, to correspond to the colors of the beads in your model. Then, based on your model, list the m-RNA bases, the t-RNA bases, and the amino acids that the sense strand of your DNA coded for.)
(teacher can use the preceeding as a header on worksheet).
As part of this unit, we see A&E's "The Race for the Double Helix", read Watson and Crick's Nobel Prize-winning paper and make a showcase to show off their models. (The showcase has pictures of Watson, Crick, and an "I Love Rosalind" picture, directions for the model, and model on the decoding sheet. To display more models, the remainder are on index cards with students' names.)
Some excellent books for student and teacher are:
- Rosalind Franklin and DNA by Anne Sayre-1975
- What Mad Pursuit by Francis Crick-1988
- The Double Helix by James D. Watson-1968
Catalog card #68-16217