A2 Genetic Control and Gene Expression 2026 Practice Test – Your Complete All-in-One Guide to Mastering Exam Success!

DNA in chromatin is wrapped around histones, forming nucleosomes that can block access to genes. Chromatin remodeling uses energy to reposition, eject, or restructure these nucleosomes, changing how tightly DNA is packaged at specific regions. By moving nucleosomes away from promoter and enhancer areas, the DNA becomes accessible to transcription factors and RNA polymerase II, allowing transcription to start. Conversely, repositioning nucleosomes over regulatory regions can hide them and repress transcription. So the main purpose is to alter nucleosome positioning to permit access for the transcription machinery. This isn’t about degrading DNA or about exporting mRNA or encoding tRNA, which are separate steps in gene expression.