Gene Regulation

What is gene expression? Gene expression means the DNA has been turned into a protein (the gene has been turned on/expressed) Remember it is the proteins that cause phenotype DNAmRNAprotein http://www.youtube.com/watch?v=OEWOZS_JTgk&safety_mode=true&persist_safety_mode=1

What does gene regulation mean? Process of turning genes on and off Causes cell differentiation Ensures appropriate genes are expressed at proper times Helps organisms respond to environment Results in differential gene expression, leading to cell specialization

Process with your partner What is meant by the term gene expression? What is meant by the term gene regulation? Why would we want to regulate a gene?

Key Vocabulary to Understand Transcription Promoter: site where RNA polymerase can bind to DNA to begin transcription Operator: segment of DNA that acts as an on/off switch for gene expression; works by controlling the ability of RNA polymerase to bind or not bind to DNA Operon: the term used to describe the promoter, operator, and genes trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on

Key Vocabulary to Understand Transcription Regulatory gene: DNA that codes for the repressor Repressor: binds to operator which turns off gene because it prevents RNA polymerase from binding In the picture below the repressor is inactivated; therefore the gene is on Corepressor: a small molecule that binds to the repressor making it active; active repressor binds to operator blocking RNA polymerase binding trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on

Polypeptide subunits that make up enzymes for tryptophan synthesis Process 1. Discuss each of the following terms: promoter, operon, operator, regulatory gene, repressor, corepressor. What determines if a gene is off or on? trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on

Polypeptide subunits that make up enzymes for tryptophan synthesis Fig. 18-3 trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on Tryptophan = Corepressor Once tryptophan binds to the repressor the repressor binds to the operator and turns off the gene. - Why is the gene turned off? DNA No RNA made Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Difference between a corepressor and inducer Corepressor: a small molecule that binds to the repressor making it active; active repressor binds to operator blocking RNA polymerase binding (TURNS OFF) Inducer: binds to the repressor; inactivates the repressor causing the repressor to leave the operator and allowing RNA polymerase to bind; turns on gene expression (TURNS ON) Similar because they both bind to the repressor

(a) Lactose absent, repressor active, operon off Fig. 18-4 Regulatory gene Promoter Operator DNA lacI lacZ No RNA made 3 mRNA RNA polymerase 5 Active repressor Protein (a) Lactose absent, repressor active, operon off lac operon DNA lacI lacZ lacY lacA RNA polymerase Figure 18.4 The lac operon in E. coli: regulated synthesis of inducible enzymes For the Cell Biology Video Cartoon Rendering of the lac Repressor from E. coli, go to Animation and Video Files. 3 mRNA mRNA 5 5 -Galactosidase Permease Protein Transacetylase Allolactose (inducer) Inactive repressor (b) Lactose present, repressor inactive, operon on

Process Describe the difference between a corepressor and an inducer???

Negative Gene Control vs. Positive Gene Control Negative control: Regulatory proteins stimulate gene expression by binding to DNA and blocking transcription Inducible Operons Repressible Operons Basically the on/off control Positive control: Regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive control) or binding to repressors to inactivate repressor function Basically the volume control; how much protein is being made A repressible operon is one that is usually on; binding of a repressor to the operator shuts off transcription (ex: trp operon) An inducible operon is one that is usually off; a molecule called an inducer inactivates the repressor and turns on transcription (ex: lac operon)

Process What is the difference between negative gene control and positive gene control?

Two Types of Negative Control Repressible operon usually on binding of a repressor to the operator shuts off transcription ex: trp operon Inducible operon usually off an inducer inactivates the repressor and turns on transcription ex: lac operon http://highered.mheducation.com/sites/9834092339/student_view0/chapter16/regulatory_proteins__regulation_by_repression.html

Polypeptide subunits that make up enzymes for tryptophan synthesis Fig. 18-3 trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on DNA No RNA made Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes Repressible Operon mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Inducible Operon Fig. 18-4 Regulatory gene Promoter Operator DNA lacI lacZ No RNA made 3 mRNA RNA polymerase 5 Active repressor Protein (a) Lactose absent, repressor active, operon off lac operon DNA lacI lacZ lacY lacA RNA polymerase Figure 18.4 The lac operon in E. coli: regulated synthesis of inducible enzymes For the Cell Biology Video Cartoon Rendering of the lac Repressor from E. coli, go to Animation and Video Files. 3 mRNA mRNA 5 5 Protein -Galactosidase Permease Transacetylase Allolactose (inducer) Inactive repressor (b) Lactose present, repressor inactive, operon on

Regulatory sequences Stretches of DNA that interact with regulatory proteins (proteins that aid transcription) to control transcription Can increase or decrease transcription Promoters: Terminators: Enhancers:

Eukaryotic Gene Expression Complex; control involves regulatory genes, regulatory elements and transcription factors that act together Transcription factors bind to specific DNA sequences and/or other regulatory proteins Some transcription factors are activators (increase expression), while others are repressors (decrease expression) The combination of transcription factors binding to the regulatory region at any one time determines how much, if any, of the gene product will be produced http://highered.mheducation.com/sites/9834092339/student_view0/chapter16/transcription_complex_and_enhancers.html

Phenotypic Differences/Cell Differentiation Gene regulation accounts for some of the phenotypic differences between organism with similar genes

Differential Gene Expression Almost all the cells in an organism are genetically identical Differences between cell types result from differential gene expression, the expression of different genes by cells with the same genome Gene expression is regulated at many stages http://highered.mheducation.com/sites/9834092339/student_view0/chapter16/control_of_gene_expression_in_eukaryotes.html

Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification DNA Gene available for transcription Gene Transcription RNA Exon Primary transcript Intron RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Figure 18.6 Stages in gene expression that can be regulated in eukaryotic cells Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function

Chromatin modification Fig. 18-6a Signal NUCLEUS Chromatin Chromatin modification DNA Gene available for transcription Gene Transcription RNA Exon Primary transcript Intron Figure 18.6 Stages in gene expression that can be regulated in eukaryotic cells RNA processing Tail mRNA in nucleus Cap Transport to cytoplasm CYTOPLASM

Transport to cellular destination Fig. 18-6b CYTOPLASM mRNA in cytoplasm Translation Degradation of mRNA Polypeptide Protein processing Active protein Degradation of protein Figure 18.6 Stages in gene expression that can be regulated in eukaryotic cells Transport to cellular destination Cellular function