Final answer:
Upon heating DNA to 95°C, adenine-thymine (A-T) bonds will separate before cytosine-guanine (C-G) bonds because A-T base pairs are held by two hydrogen bonds, whereas C-G base pairs are held by three hydrogen bonds. This phenomenon is a critical part of DNA denaturation during PCR. The A-T rich regions denature first because of the weaker hydrogen bonding compared to C-G rich regions.
Step-by-step explanation:
If DNA is heated to 95°C, the bonds between complementary strands break, resulting in two single strands of DNA. In this process, the bonds between the cytosine (C) and guanine (G) base pairs will separate last because these base pairs are stabilized by three hydrogen bonds, as opposed to the two hydrogen bonds that stabilize adenine (A) and thymine (T) base pairs. Therefore, A-T bonds will separate first when DNA is heated since they are held together by fewer hydrogen bonds compared to C-G bonds.
DNA denaturation occurs due to the disruption of hydrogen bonds when DNA is subjected to high temperatures, as in Polymerase Chain Reaction (PCR). During the PCR process, DNA strands are separated, or 'melted', to allow for the replication of DNA, where primers anneal to single strands at lower temperatures.
Ultimately, the A-T rich regions of the DNA will 'melt' first during denaturation, due to the weaker binding provided by two hydrogen bonds, whereas C-G rich regions with their three hydrogen bonds denature at higher temperatures.