the extra through after both sugar-phosphate strands are complete.)
- Using needle-nose pliers to "tie-off" the or twist the ends of each wire will save your fingertips. Also, remember that it is easier to thread the wire directly through the beads while they are in the dish rather than trying to pick up the beads with your fingers.
NOTE: Except where noted otherwise, the procedure of making key chains,earrings, bracelets, etc.. is exactly the same. To make earrings, you might prefer the small (1.5 mm dia.) seed beads; to make keychains, use the larger (3 mm dia.) E-beads.
- Step 1: Decide which colors you want to use for your model (you will need to choose beads of six different colors - two different colors for the sugars and phosphates, and four different colors for the base pairs.
- Step 2: To make a keychain, earrings, pendant, or central molecule for a silk cord necklace, bracelet, or ankle bracelet, cut two 15 cm (6") strands of wire. Twist two wires together at one end to prevent beads from slipping off as you string them. These strands of wire will be the helixes, or "uprights" of your DNA model.
- Step 3: String an equal and even number of beads of alternating colors onto each of the wires, to represent alternating sugars and phosphates. Make sure to start with the same color bead on each wire. When you have strung the beads on each of the wires, twist a loop at the tops of the "uprights" separately to prevent the beads from falling off. Use a minimum of 26 beads for the basic 2 inch molecule. (when twisted) (Leave one inch of "slack" at the top. If you bead right to the top, it'll be very difficult to wire the bases.)
- Step 4: Cut 30 cm (12") of wire and fold it in half to make an elongated "U". Next, string and center two different colored beads on the wire (or each wire, for earrings), to form the first "rung" or pair of nitrogenous bases.
- Step 5: Thread each end of the wire with the "bases" beads through the third and fourth beads from the bottom of each of the sugar and phosphate "uprights" and 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 i