Final answer:
UV light can cause changes in the accessibility of DNA by inducing methylation and acetylation of histones, and denaturation of DNA involves the separation of double strands into two single strands.
Step-by-step explanation:
UV light can cause changes in the accessibility of DNA by inducing methylation and acetylation of histones, which pack the DNA more tightly and make it less accessible to interact with UV light (double strands of two single strands of DNA). Methylation and acetylation of the genes can also alter the accessibility and transcription of DNA. Denaturation, a physical property of DNA, when subjected to extremes of pH or high temperatures, causes the double helix to unfold and separate into two single strands. The denatured DNA can be reannealed by cooling or removal of the denaturants.