Introduction: LED DNA Model

About: I am a middle school computer teacher with an EE degree. I do programming to pay for my teaching habit. I am also one of the founders of LVL1 - Louisville's Hackerspace.

This awesome Instructable was built by my daughter for her advanced biology class in high school.  Admit it, ever since you saw pretty LEDs you have thought about building a DNA model.  Well here are the instructions for just that.   This is not just your basic double helix model, this model consists of several DNA pairs, representations of enzyme molecules and shows how DNA splits and replicates.  My daughter does not mess around when it comes to her schoolwork!

Now you might say that she cheated and just had me just show her everything to do, but she did not.  I helped her breadboard the initial LEDs so she could see how they work and I showed her how to solder a DNA pair.  After that, armed with a soldering iron, off she went.  She put this together on a Sunday afternoon.

Step 1: Gather Your Parts...

You will need:
  • 9 Volt battery and battery holder - I had one with a switch built in. 
  • Lots of 100 Ohm resistors, buy 1 per DNA pair.  Go ahead and buy a hundred, they are cheap.
  • Breadboard for testing
  • Soldering Iron and solder
  • Helping hands or duct tape to assist with the holding of the pieces to be soldered.
  • Green LEDs - When buying LEDs, get the 5mm ones - I bought many various colors and we tested a bunch of different color combos
  • Red LEDs - twice as many Red LEDs than the Green ones
  • Blue LEDs
  • Yellow LEDs - twice as many Yellow LEDs than the Blue ones
  • Romex Electrical wire (12 Gauge) - Home Depot or Lowes
  • Electrical Tape
  • Big Capacitors
  • 2 bigger (physical size) 100 Ohm resistors - to represent the Helicase molecule
  • Piece of wood for the base
You can get resistors, capacitors, breadboards, battery holders, etc from Jameco.  The LEDs I bought are from out of St. Louis.  You can buy cheaper LEDs from China (ebay)  if you have time to wait for shipping.  Still, I like to buy American when I can.

Step 2: Breadboard a LED Circuit

Start by connecting your 9V battery (and holder) to the power strips on the breadboard. Connect the Positive side of the battery to the red rail on the breadboard, connect the negative side to the black rail.  Then connect the long lead of a green LED to the red (+) side of the breadboard, connect the other side to one side of the 100 Ohm resistor.  Connect the other side to the long end of the first Green LED, then follow with the next LED in series and then to ground.

It is important to use a breadboard, because you can set up the circuit and have it light prior to soldering.  If you put the LEDs in backwards, it will not work but it will not destroy the led.  If you try powering an LED without using the resistor, you will 'let the magic smoke' out of the LED!  The resistor acts as a current limiter to the circuit.  This circuit needs 9V because each LED has a voltage drop.  You can try hooking it up to 6V, but it probably will not work.

Now build another DNA strand with one Blue and Two Yellow LED's.

Step 3: Solder a Strand

Heat up your soldering iron, clean the tip and begin soldering the strands.  Carefully remove the breadboarded circuits, one component at a time, so you do not accidentally mess up the orientation of the LEDs.  Solder the leads together carefully.  Helping hands with alligator clips can be helpful as well as just taping the components to the table fol soldering.  When you have completed a strand, hook it back into the breadboard to test that it still works. 

Follow this procedure to make as many strands as you need.  You will need half as red/green and half as red/blue.

Step 4: About DNA and This Model

DNA is a very complex molecule.  My daughter did her best to represent this molecule with leds by studying how dna is actually built.  As you see there AT and GC pairs.  These are represented by the various colored LED's.  There is also a Hydrogen bond holding the A to the T and the G to the C.  This is represented with the resistor.  The outside of the helix is represented by the colored tape on the copper wires.

When DNA splits and replicates, there are other enzymes that make that happen.  Those enzymes are represented by the large capacitor (which has no effect on the circuit, whatsoever) and the larger 100Ohm resistor (which does the same thing as the smaller resistor)  See the legend in the picture for the actual enzyme names.

If you are building this for biology class, this is a good time to figure all of this out.  I am sure you will get tested on it!!!

Step 5: Build the Base and the Supports

Get a piece of scrap wood and drill two holes to support the copper wire.  Sarah got some old house wire scraps and cut the insulation off for the side posts of the structure.  Glue the wire into the wood if it looks like it needs it.

Step 6: Attach the DNA Strands

Electrify the sides by connecting the battery box.   Solder the power to the base.  Solder the strands in place as you build your DNA strand.  Start rotating the strand as you build.  The copper wire makes it easy to make a nice double helix!

Step 7: Start the Split

The last strand of the DNA contains the Helicase molecule instead of the Hydrogen bond.  Use a (physically) larger 100 Ohm resistor to represent this molecule (Helicase).  Then the next strand can be a split strand with no resistor and it does not light up.  See and study the pictures.

After you have built about 6 to 8 strands going up you will want to split your model into two strands.  Here is where you have to pay careful attention to what is positive and negative.  You will need to cut a couple more pieces of thick copper wire for the 'other side' of the split pieces.  It is important to look at the drawing to see where the power is on this circuit.  You do not want to accidently short the battery + and - on the model.  Sarah soldered two piece of white copper to jumper the outside + and - to the inside + and - of the split.

Step 8: Wire the Split

Continue wiring up the split, soldering and testing as you go.  Soldering is fun, isn't it!  Attach a big capacitor the the base of the split.  This represents the splitting molecule, Polymerase.  Keep bending the wire and shaping the DNA model as needed.

Step 9: Create the Legend and Finish!

Create the legend and glue it onto the block.  Also use double stick tape to glue the battery holder to the wooden base.  Finally use tape to create the sugar and phosphate groups up the side of the DNA model.  Sarah used green and yellow electrical tape.  This is your model, you can use whatever colors suit you best!

Finally, take your model into class and smile big!  You just created something awesome!

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