Take two pieces of string that are approximately 10 inches each, and create a double helix by wrapping them around each other to make 10 complete turns. Tape one end of the strings to a table, and now twist the strings three times (360° each time) in a right-handed direction. Note: As you are looking down at the strings from above, a right-handed twist is in the clockwise direction.
A. Did the three turns create more or fewer turns in your double helix? How many turns are now in your double helix?
B. Is your double helix right-handed or left-handed? Explain your answer.
C. Did the three turns create any supercoils?
D. If you had coated your double helix with rubber cement and allowed the cement to dry before making the three additional right-handed turns, would the rubber cement make it more or less likely for the three turns to create supercoiling? Would a pair of cemented strings be more or less like a real DNA double helix than an uncemented pair of strings? Explain your answer.