Chapter 24, Problem 34CQ

Summary Introduction

To explain: How the Tm of DNA decreases with increasing [Na⁺].

Concept introduction: Melting temperature (Tm) is the temperature at which half of the DNA melts or denatures due to a break in the hydrogen bond that holds the two strands together. Melting temperature of a DNA duplex highly depends on two factors such as the ionic strength of the solution and the guanine-cytosine content of the DNA helix. Both factors are directly proportional to the melting temperature, that is, an increase in the ionic strength and G-C content will increase the melting temperature, and vice versa. However, extreme high concentration of ions destabilizes the DNA structure and thereby decreases the melting temperature.