Final answer:
Chromatin-remodeling complexes use ATP hydrolysis to rearrange nucleosomes on the DNA, affecting the accessibility of certain DNA regions to proteins and thereby regulating gene expression. By altering the chromatin structure, these complexes play a crucial role in gene expression regulation and can impact cellular processes, which, if disrupted, can lead to diseases such as cancer.
Step-by-step explanation:
Chromatin-remodeling complexes are essential in regulating gene expression in eukaryotic cells. These complexes use the energy from ATP hydrolysis to alter nucleosomes, which are the fundamental units of chromatin consisting of DNA wrapped around histone proteins. This remodeling process adjusts the DNA-histone interaction and either relaxes or tightens the chromatin structure, making certain regions of DNA more or less accessible to other proteins that play a role in processes such as transcription, DNA repair, and replication.
These complexes can move, slide, or reposition nucleosomes along the DNA, which is crucial for the regulation of gene expression. The changes induced by chromatin-remodeling complexes are not permanent and can be reversed depending on cellular needs. Various modifications, such as the addition of methyl, acetyl, or phosphate groups to histone tails, play a role in signaling whether a region of chromatin should be open or closed, thus controlling how tightly DNA is wound around histones and affecting the accessibility of transcription machinery.
While chromatin-remodeling complexes don't add methyl groups to histones (that's the role of different enzymes known as histone methyltransferases), they are indeed responsible for repositioning nucleosomes and therefore play a key role in modulating chromatin structure and enabling the correct functioning of cellular processes. Abnormalities in chromatin remodeling can lead to diseases such as cancer, as proper regulation of gene expression is paramount for normal cell function.