The melting profile for a DNA is found to differ in two different salt solutions.In 0.001 M NaCl,T_m = 55° C,and in 0.01 M NaCl,T_m = 65°C. The fundamental reason for this change is A) higher salt concentration increases the electrostatic repulsions between phosphates B) the base stacking is more effective in high salt C) hydrogen bonding between complementary bases in enhanced at high salt D) higher salt concentration decreases the electrostatic repulsions between phosphates

Question

Quizplus · Accepted Answer

The electrostatic repulsion between the negatively charged phosphate groups along the DNA backbone can destabilize the DNA double helix and decrease its melting temperature (Tm). The higher salt concentration in 0.01 M NaCl can shield the negative charges on DNA and reduce the electrostatic repulsion, thus stabilizing the DNA duplex and increasing its Tm compared to 0.001 M NaCl. Therefore, choice D is the best answer. The other choices are not supported by experimental evidence and do not explain the observed difference in DNA melting profiles.

The Melting Profile for a DNA Is Found to Differ