Final answer:
Eukaryotic DNA is packaged with proteins known as histones into structures called nucleosomes. These compact structures must be unwound for transcription to occur. Environmental factors can influence DNA packaging and thus gene expression, a concept known as epigenetics.
Step-by-step explanation:
Eukaryotic DNA is packaged with proteins into structures that must be opened before transcription can occur. These proteins are called histones, which are critical for wrapping DNA into compact units known as nucleosomes. Nucleosomes further fold and coil to form chromatin, the material that makes up chromosomes. During transcription, specific transcription factors and other regulatory proteins access the DNA by unwinding these compact structures to promote the transcription process. Furthermore, the study of epigenetics shows us that DNA packaging can be influenced by environmental factors, affecting gene expression without altering the nucleotide sequence.