1. Gene Control Chapter 11

2. 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

3. 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]

4. 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

5. 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

6. 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