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Transcript
Gene Control Chapter 11 Prokaryotic Gene Regulation Operons, specific sets of clustered genes, are the controlling unit Promoter: sequence where RNA polymerase binds Requirement for initiation of transcription Operator: sequence between the promoter and start of gene Repressor binds to the operator RNA polymerase can’t move toward the gene Removed by signal molecules that bind to repressor Shape changes can’t bind Activators make the promoter more accessible Assists unzipping of DNA at promoter site Signal molecule binding regulates Repressors and activators aren’t antagonistic Lac Operon as a Model of Control • Production of enzymes to break down milk sugar • An activator and repressor have roles • Conditions tightly controlled – Lactose must be high, but no other sugar present – [Lactose] and [glucose] Trp Operon • AA tryptophan necessary for all life • Only repressor has role • Opposite mechanism of lac operon – Repressor can’t bind without Trp • RNA polymerase binds – Trp binds to repressor = shape change • RNA polymerase blocked Eukaryotic Gene Regulation • Chromatin structure – Promoters blocked from transcription factors • DNA wraps around proteins called histones, forming nucleosomes • Changes during cell cycle – Methylation (-CH3) of DNA ensures ‘off’ genes stay off • Transcriptional control – Transcription factors (major) • Activators bind to enhancers • DNA bends to allow interaction of enhancer with promoter so RNA polymerase can bind – 1 promoter per gene • Silencers prevent Eukaryotic Gene Regulation (cont.) • mRNA processing – Alternate RNA splicing • Change how exons recombine • 1 gene can code many polypeptides • Translational control – Life span of mRNA • Enzymes degrade or allow to be translated – Prokaryotic is short lived = quick adaptation – Eukaryotic varies – Protein requirements • Protein structure – Levels of protein folding (1°, 2°, 3°, 4°) – Cleavage of proteins – Selective breakdown/denaturation
