EXPERIMENTAL FIGURE 5-7 G·C content of DNA affects melting temperature. The temperature at which DNA denatures increases with the proportion of G·C pairs. (a) Melting of double-stranded DNA can be monitored by its absorption of UV light at 260 nm. As regions of double-stranded DNA unpair, the absorption of light by those regions increases almost twofold. Light absorption by single-stranded DNA changes much less as the temperature is increased. (b) The temperature at which half the bases in a double-stranded DNA sample have denatured is denoted T_m (for “temperature of melting”). The T_mis a function of the G·C content of the DNA; the greater the G+C percentage, the higher the T_m.