Drill 8 holes in the wooden dowel evenly spaced along its length. Drill through the dowel completely. These holes will be where the strands of DNA rest. Secure the wooden dowel to the block by drilling through the center of the block and screwing a 3 inch screw into one end of the wooden dowel. Encircle the dowel's end with wood glue where it is mounted to the wooden block. This will add durability. Allow this to dry.
Divide your 1/2 inch Styrofoam balls into 4 piles of 4 balls each; these piles will be the base components of the DNA. DNA has four main chemicals that combine in pairs. These pairs form the strands inside the DNA. The four chemicals are adenine and thymine, which pair together and guanine paired with cytosine.
Pair your 1/2 inch Styrofoam balls -- blue for adenine, yellow for thymine, red for guanine, and green for cytosine. Adenine and thymine should be paired together; stick a toothpick completely through all the blue balls. Stick the same toothpick through the holes in the wooden dowel. Stick a yellow ball on the toothpick. Glue in place and let dry. Repeat with the guanine paired with cytosine (red and green). Each strand (each toothpick pair) should alternate, so that no adenine/thymine pair is right next to another.
Cut two 8 inch segments of kite string. Glue an end of each kite string to the wooden block an inch from the dowel's location. Allow to dry.
Paint the 1 inch Styrofoam balls purple. Once the balls are dry, thread 7 onto the kite string tightly using a large sewing needle. Press the outside of the DNA helix to the toothpick DNA strands. Add glue to secure, if needed. Repeat with the second kite string.
Glue the threaded kite strings to the top of the dowel. This will cause the purple Styrofoam balls to the top of the dowel to form the top turn of the helix.