Final answer:
The melting temperature of nucleic acid is when the hydrogen bonds between base pairs break, causing the DNA strands to separate. The temperature at which this occurs depends on the G=C content; higher G=C content results in a higher melting temperature.
Step-by-step explanation:
The melting temperature of nucleic acid is the temperature at which the hydrogen bonds between the nucleotide base pairs begin to break apart, causing the two strands of DNA to separate or "melt". This can happen when the substance is subjected to temperatures typically above 80 to 90 degrees centigrade. The temperature at which 50% of the DNA is denatured is referred to as the Tm (melting temperature), and it varies depending on the G=C content in the DNA; the higher the G=C content, the higher the Tm. During this denaturation process, as the temperature increases, the absorbance value for the sample increases, indicating the separation of double-stranded DNA. Conversely, if the temperature is brought back to a normal biological range slowly, the strands can anneal, reforming the double helix structure.