Cut the string into two 10-inch segments.
Cut the licorice sticks into one-inch segments. Thread a red piece of licorice onto each string. Alternate adding black and red pieces until each string is full, leaving a little room on each end. These segments represent the sugar and phosphate combination that forms the basic structure of the DNA.
Assemble the gummy bears by color. Create two color pairs, such as orange/blue and red/green. These combinations represent the adenine/thymine and guanine/cytosine chemical-base pairs that determine the genetic material contained by the DNA strand.
Thread two gummy bears of the same color onto a toothpick. Insert a marshmallow. Add a pair of gummy bears in the other color. For example, a strand could have two orange gummy bears, a marshmallow, and two blue gummy bears. The marshmallow represents the hydrogen bond that connects the bases.
Insert the ends of the toothpicks into each of the red licorice pieces. When complete, these should resemble ladders leading to the red licorice strands .
Connecting the two pieces of string at each end, twist the top of the finished model counterclockwise to create the correct double helix shape.