The Double Helix -a DNA Model With Lights

DNA models have been made from a lot of different things; candy, Styrofoam, KNEX, etc. I've even made a couple of models myself from beads, but surely there should be a model made from LEDs....

What You Will Need:

Materials:

Base or stand -I used a dollar store jewelry box made of wood.
LEDs -5 different colours 20 total,8 white and 3 each of the other colours.
The appropriate resistors.
Power supply, with enough voltage to power the circuit (I used a 9v adapter).
Wires -white preferably
Electrical tape -white preferably
On/off switch.
Floral stem wire (18 gauge)
#6 plastic (polystyrene) -it is the clear plastic often used in takeout containers.
Clear vinyl tubing ~2 feet long, 7/16 inch diameter.

Tools:

Soldering iron, solder etc.
Scissors, and X-acto knife.
Drill, Dremel
Sandpaper
Glue (Weldbond)
Toaster oven, oven mitt and parchment paper

Making the Basepairs

If you are fortunate to have access to a laser cutter, you could create the base pairs with more detail, since I'm not that lucky, I had to simplify them.

I used #6 (PS) plastic, cut out the shape and shrunk it in the oven, a cool trick I learned from the following instructable: https://www.instructables.com/id/Doodle-Earrings-Jewelry-Charms-by-Recycling-6-p/.

One important thing to note is that the plastic doesn't always shrink to the same degree. Before you start cutting out your base pairs, cut a small piece of the plastic, measure it (length and width), shrink it in oven and then measure the end product and use that to adjust the size of your template.

A) I wanted the base pairs to be 7cm in length, so I resized the template accordingly, and printed it out.

B) Using an X Acto knife, and the template (right click and save image below) as a guide, cut out a base pair.

C) With fine sandpaper, sand the base pairs (I left the hydrogen bonds unsanded).

D) Place the plastic base pair onto the parchment paper and into a toaster oven.

E) Set the oven to 250 F, and watch, first the plastic starts to curl, then it uncurls, then it shrinks.

F) With an oven mitt take out the parchment paper, if it is still a bit curled, place something heavy on top, such as a text book.

G) Make six of these, three A-T and three G-Cs.

Check out the above instructable for more information on shrinking #6 plastic.

Making the Base

I found a wooden jewelry box at a dollar store which I used as the base or stand for my model, the dimensions are 13L X 9W X 4H (cm), with the lid removed.

First unscrew the hinges and remove the lid.
Mark on the back where the on/off switch is to go, and cut a slot in the wood using a drill and a Dremel.
Drill two holes about 0.5-1cm in diameter and about 4cm apart centred on the top of the base. These are for the wires to pass through.
Make a small notch on the bottom back of the base for the adapter wire to pass through.

Wiring the Lights

I had a bit of trouble getting my circuit to work, I initially tried to string all the LEDs together in parallel with one resistor. This didn't work and I started to think that may be I should stick to doing cell biology. Fortunately, Instructables has an Answer section, where I posted my problem, and I got the help I needed to get my circuit to work (thanks to everyone who answered my question!)

What I needed to do was to keep the LEDs with different voltages on a separate parallel group with its own resistor. So in my case I had two branches of the white, blue and green (same voltage) LEDs in parallel with the appropriate resistor (as calculated with led calculator). And two branches of the red LEDs with the appropriate resistor. I need the two branches of each for the each strand of DNA. (You may be wondering what happened to the yellow LEDs, these would likely be grouped in with the red, that is if I had any, which I don't, so what I did was use white LEDs and coloured them with a yellow Sharpie.)

I've included the colour pattern below, the blue is paired with the red (3 pairs) and the yellow is paired with the green (3 pairs). These LEDs will light up the base pairs. The white LEDs light up the sugar-phosphate backbone (4 on each strand). These LEDs should be spaced 3-4cm apart.

The wires were then stuffed through the two holes in the wooden based and then soldered to the on/off switch and the 9v power supply.

Bend the LEDs for the base pairs (red, blue, green, and yellow) so that they are perpendicular to the wire, the white LEDs should be pointing upward.

When I made sure everything worked, I wrapped up any exposed wires with white electrical tape.

Wraping Wire

Wrap the floral stem wire with the white electrical tape, you will need two of these. I did this so that it looks nicer and ensures the metal doesn't contact the wires in the circuit.
Poke the floral stem wires through each hole in the base (as far as they will go). Then tape the two LED strands and the floral stem wire together with the white tape.
Since the bottom of the base(stand) is open, I put some tape across it so that the wires don't hang out.

Basepairs and the Sugar-phosphate Backbone

Cut pieces of clear vinyl tubing so that they fit between the LEDs (base pairs).
Make a slit down the length of each tube so that they can easily be slipped around the wires.
Glue each plastic base pair in place (glue them right onto the LED). Make sure you are consistent; ie; red= thymine, blue= adenine, yellow=guanine, green=cytosine.

Finishing Up

Once the glue has dried completely (I waited until the next day), gently grasp each DNA strand and twist. Although the double helix is really a double corkscrew shape, this is difficult to achieve and is often depicted as a twisted ladder instead, which is the look I'm going for.

Twist together the two ends of the floral stem wire so that they won't come undone and trim off the excess wire.

Cover ends with the vinyl tubing and you are done!