A Model of DNA

Objective: To construct a model of double-stranded DNA.

Materials: cardboard tube from paper-towel roll, 10 toothpicks, felt-tip markers (two colors), thumbtack,

metric ruler (You could use other materialsget inventive!)

Procedure: Create a 3-D live model of DNA with Sugars and Phosphates labeled. (Here is one way) 1. The typical tube has a seam that spirals up the tube. It is a helix. Outline the spiral seam with a

colored marker.

2. Using a different-colored marker, draw a second spiral midway between the lines of the first.

These two spirals represent the two strands of double-stranded DNA.

3. Measure along the tube and mark a dot on each spiral every 5 cm. Label each dot with the letter

S to indicate a sugar unit. Make a hole in the spirals at each S mark with a thumbtack.

Move down each spiral and mark a letter P to indicate a phosphate group halfway between

each two S dots.

4. Color each toothpick along half its length with a marker. A toothpick represents a base pair in

the DNA molecule.

5. Starting at the top of the tube, insert a toothpick in one hole at an S label and guide it so it

emerges through the S on the opposite side of the tube. Repeat the process for the other

holes.

Analysis:

1. Are the bases on the interior or the exterior of the double helix? Are they randomly arranged or

neatly stacked?

2. Are the phosphate groups on the exterior or interior of the DNA structure?

3. Are the sugar groups on the interior or exterior of the DNA molecule?

4. Make sure to include your model or take a picture of it when you turn in your lab.