Toothpicks, straws and colored marshmallows (you can buy those) works really good. Oh, and either tape or a hot glue gun.
Use the straw as the central shaft (I know DNA doesn't have that but for simplicity's sake you need one). Use scissors to snip holes in the straw to push the toothpicks through, one on each side. Glue them in. Go up the shaft of the straw, rotating the holes for the toothpicks as you go up to get the familiar spiral. Once you're done, pick out for marshmallow colors (GCAT, anyone?) and push them onto the toothpicks.
No idea how well this will work! I just made it up! But with a hot glue gun it should work great. Oh, and for a base to hold it up... use a paper plate or something. Place the plate upside down, cut a hole for the straw, and glue it in place. Do NOT use a styrafoam plate if you're using hot glue. The plate will melt lol.