Regulation of Gene Expression Results in differential gene expression, leading to cell specialization Gene Expression Review
• Inherited information flows from DNA to RNA to protein through the processes of transcription and translation
Gene Expression Regulation • Gene expression can be regulated: – Before transcription – After transcription – After translation
But first we must expose the gene by unpacking the DNA….. Histone Acetylation
• Addition of acetyl groups (-COCH3) to histones – opens up chromatin (“on”) • Promotes transcription of specific genes DNA Methylation • Addition of methyl groups to DNA • Methylated DNA is not expressed (gene “off”) • Inactive genes are heavily methylated • Remove methyl groups – genes are activated MECP2 Acetylation and Methylation
Epigenetics
• External or environmental factors that modify the activation of certain genes (do not change the DNA sequence) • Epigenetic factors affect histone modification (through acetylation) and DNA methylation Exposed Gene Gene Structure Regulatory Sequences and Regulatory Genes • DNA regulatory sequences, regulatory genes, and small regulatory RNAs are involved in controlling gene expression
1. Regulatory sequences: stretches of DNA that interact with regulatory proteins to control transcription 2. Regulatory genes: a sequence of DNA encoding a regulatory protein or RNA Regulatory Sequence
• Promoters, terminators and enhancers are all examples of regulatory sequences “Switch” • Regulatory sequences interact with regulatory proteins (coded for by regulatory genes) to act like a molecular “switch” turning genes on and off Regulatory Sequence: Enhancers
• A short region of DNA upstream from a gene that activates transcription of a gene • Part of the molecular “switch” Enhancers Regulatory Genes
• A sequence of DNA encoding a regulatory protein or RNA • MicroRNAs (miRNAs) are produced by regulatory genes Gene Regulation in Eukaryotes Gene Regulation in Eukaryotes
• More complex that prokaryotic gene regulation because eukaryotic genes are controlled individually • Involves regulatory genes, regulatory sequences and transcription factors that all work together Gene Regulation in Eukaryotes
• Transcription factors bind to specific DNA sequences and/or other regulatory proteins • Determine how much of a gene product will be produced
1. Activators: increase gene expression by promoting transcription (ex. MyoD)
2. Repressors: decrease gene expression by inhibiting transcription (ex. p21 protein) Activators Repressors Gene Regulation In Prokaryotes Prokaryotic Gene Regulation
• Both positive and negative control mechanisms regulate gene expression in prokaryotes (bacteria) • Operon: cluster of genes under the control of a single promoter (less complex gene regulation) • Examples: – Lac operon (inducible operon) – Trp operon (repressible operon) Operon: Basic Structure Lac Operon
• An inducible operon because it is usually turned OFF but can be stimulated (induced) • The sugar allolactose acts as the inducible molecule (inducer)
Trp Operon
• A repressible operon because it is usually turned ON but can be inhibited (repressed) • Tryptophan acts as the repressor molecule
Negative and Positive Control
• Negative control: regulatory proteins inhibit gene expression by blocking transcription of the gene • Positive control: regulatory proteins stimulate gene expression by promoting transcription of the gene • Both the lac operon and the trp operon have positive and negative control elements Negative Control
Positive Control