Final answer:
Chromatin remodeling complexes reposition nucleosomes to expose regions of DNA for gene expression by making the DNA accessible to transcription machinery like RNA polymerase and transcription factors.
Step-by-step explanation:
Chromatin remodeling complexes reposition nucleosomes, allowing access to important regions of DNA. When nucleosomes are repositioned, they enable the DNA to be more accessible for processes such as transcription. This remodeling is necessary for the transcriptional machinery, which includes RNA polymerase and transcription factors, to initiate the transcription of a gene. In a tightly packed chromatin structure, nucleosomes are spaced closely together, preventing these factors from binding to the DNA. Once remodeled through nucleosome repositioning, gene expression can occur as the transcription factors are able to bind to the now-exposed DNA.
Chromatin remodeling is also associated with epigenetic changes that can alter gene activity without changing the underlying genetic sequence. Epigenetic changes like methylation and histone modification can influence the spacing of nucleosomes, further regulating gene expression. These changes are potentially heritable and can affect biological processes significantly, even influencing the development of diseases such as cancer.