Tiêu đề 23. GENE EXPRESSION.pdf ✅

PHARMD GURU Page 4  Mechanism: Often function through CTCF (CCCTC-binding factor), which organizes chromatin structure.  Function: Maintains proper gene expression by preventing inappropriate regulatory influence. 5. OPERATORS AND OPERONS (PROKARYOTIC REGULATION):  Operator: DNA sequence acting as a binding site for repressor proteins, controlling gene transcription.  Operon: A cluster of genes regulated together under a single promoter.  Example: Lac operon in Escherichia coli, which regulates lactose metabolism based on environmental availability. 6. EPIGENETIC MODIFIERS: a) NUCLEOSOMES AND HISTONES:  DNA is wrapped around histone proteins to form nucleosomes, affecting gene accessibility. b) HISTONE MODIFICATIONS:  Histone Acetylation: Increases transcription by loosening chromatin.  Histone Deacetylation (HDACs): Removes acetyl groups, condensing chromatin and reducing transcription. c) DNA METHYLATION:  Addition of methyl groups to cytosine residues (typically in CpG islands) represses gene expression by compacting chromatin. 7. UNTRANSLATED REGIONS (UTRS):  5' UTR: Influences translation initiation and mRNA stability.  3' UTR: Contains regulatory elements affecting mRNA degradation and localization.