Which of the following is the best reason as to why the strands of a DNA molecule are more easily separated at pH > 11?
A) At pH 11 the cross-strand negative charge repulsion becomes so strong that the two strands are much more easily separated.
B) Most biomolecules precipitate when the pH is greater than 11. Upon precipitation the two strands are much more easily separated.
C) Any solution above pH 11 is considered highly caustic and therefore many of the covalent bonds, especially between the nitrogenous bases and the C1' sugars, will be hydrolyzed at this extreme pH.
D) The pKa values for some of the hydrogen bond donor groups (e.g., R-H2) are lower than 11 and therefore these groups will become deprotonated at pH values above 11. The deprotonated form of these groups cannot form the favorable cross-strand hydrogen bonds that hold the two strands together.