350 Chapter 9. Cooperative transitions in macromolecules[[Student version, January 17, 2003]]
under electrophoresis as though|M|had suddenly decreased to|M|−∆M. The quantity ∆M
appears on the vertical axis of the graph.
a. Find the critical torqueτcrit,beyond which the transition happens, from the data on the graph.
b. Find the numberK defined above, that is, the number of basepairs per left-handed turn of
Z-DNA. Compare to the accepted valueK≈12.
c. How much energy per basepair does it take to pop from B- to Z-form? Is this reasonable?
d. Why do you suppose the transition is so sharp? (Give a qualitative answer.)