Regulation of Gene Expression Chapter 18 Regulation of Gene Expression

Eukaryotes, gene expression regulates development Prokaryotes and eukaryotes alter gene expression in response to their changing environment Eukaryotes, gene expression regulates development RNA  many roles in regulating gene expression in eukaryotes © 2011 Pearson Education, Inc.

Regulation of gene expression in bacteria Natural selection production of only products needed by that cell Gene expression in bacteria = operon model © 2011 Pearson Education, Inc.

Regulation of gene expression Figure 18.2 Precursor Feedback inhibition trpE gene Enzyme 1 trpD gene Regulation of gene expression Enzyme 2 trpC gene  trpB gene  Figure 18.2 Regulation of a metabolic pathway. Enzyme 3 trpA gene Tryptophan (a) Regulation of enzyme activity (b) Regulation of enzyme production

Figure 18.3 trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Operator Regulatory gene RNA polymerase Start codon Stop codon 3 mRNA 5 mRNA 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. mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Polypeptide subunits that make up enzymes for tryptophan synthesis Figure 18.3a trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Operator Regulatory gene RNA polymerase Start codon Stop codon 3 mRNA 5 mRNA 5 E D C B A Protein Inactive repressor Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes. Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on

Tryptophan (corepressor) Figure 18.3b-1 DNA mRNA Protein Active repressor Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes. Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Tryptophan (corepressor) Figure 18.3b-2 DNA No RNA made mRNA Protein Active repressor Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes. Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Repressible and Inducible Operons: 2 Types of Negative Gene Regulation A repressible operon is one that is usually on; binding of a repressor to the operator shuts off transcription The trp operon is a repressible operon An inducible operon is one that is usually off; a molecule called an inducer inactivates the repressor and turns on transcription © 2011 Pearson Education, Inc.

The lac operon is an inducible operon and contains genes that code for enzymes used in the hydrolysis and metabolism of lactose © 2011 Pearson Education, Inc.

Figure 18.4 Regulatory gene Promoter Operator DNA 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. 3 mRNA mRNA 5 5 Protein -Galactosidase Permease Transacetylase Allolactose (inducer) Inactive repressor (b) Lactose present, repressor inactive, operon on

(a) Lactose absent, repressor active, operon off Figure 18.4a Regulatory gene Promoter Operator DNA DNA lacI lacZ No RNA made 3 mRNA RNA polymerase 5 Figure 18.4 The lac operon in E. coli: regulated synthesis of inducible enzymes. Active repressor Protein (a) Lactose absent, repressor active, operon off

Allolactose (inducer) Figure 18.4b lac operon DNA lacI lacZ lacY lacA RNA polymerase 3 mRNA mRNA 5 5 -Galactosidase Permease Transacetylase Protein Figure 18.4 The lac operon in E. coli: regulated synthesis of inducible enzymes. Inactive repressor Allolactose (inducer) (b) Lactose present, repressor inactive, operon on

Eukaryotic gene expression regulated at many stages All organisms must regulate which genes are expressed at any given time © 2011 Pearson Education, Inc.

Differential Gene Expression Differences between cell types result from differential gene expression, the expression of different genes by cells with the same genome Abnormalities in gene expression can lead to diseases including cancer © 2011 Pearson Education, Inc.

Gene available for transcription Figure 18.6a Signal NUCLEUS Chromatin Chromatin modification: DNA unpacking involving histone acetylation and DNA demethylation 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

Protein processing, such as cleavage and chemical modification Figure 18.6b CYTOPLASM mRNA in cytoplasm Translation Degradation of mRNA Polypeptide Protein processing, such as cleavage and chemical modification 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 (such as enzymatic activity, structural support)

Amino acids available for chemical modification Figure 18.7 Histone tails DNA double helix Amino acids available for chemical modification Nucleosome (end view) (a) Histone tails protrude outward from a nucleosome Figure 18.7 A simple model of histone tails and the effect of histone acetylation. Unacetylated histones Acetylated histones (b) Acetylation of histone tails promotes loose chromatin structure that permits transcription

DNA Methylation DNA methylation  reduced transcription © 2011 Pearson Education, Inc.

Organization of a Typical Eukaryotic Gene © 2011 Pearson Education, Inc.

Enhancer (distal control elements) Proximal control elements Figure 18.8-1 Enhancer (distal control elements) Proximal control elements Poly-A signal sequence Transcription start site Transcription termination region DNA Exon Intron Exon Intron Exon Upstream Downstream Promoter Figure 18.8 A eukaryotic gene and its transcript.

Enhancer (distal control elements) Proximal control elements Figure 18.8-2 Enhancer (distal control elements) Proximal control elements Poly-A signal sequence Transcription start site Transcription termination region DNA Exon Intron Exon Intron Exon Upstream Downstream Promoter Transcription Poly-A signal Primary RNA transcript (pre-mRNA) Exon Intron Exon Intron Exon Cleaved 3 end of primary transcript 5 Figure 18.8 A eukaryotic gene and its transcript.

Enhancer (distal control elements) Proximal control elements Figure 18.8-3 Enhancer (distal control elements) Proximal control elements Poly-A signal sequence Transcription start site Transcription termination region DNA Exon Intron Exon Intron Exon Upstream Downstream Promoter Transcription Poly-A signal Primary RNA transcript (pre-mRNA) Exon Intron Exon Intron Exon Cleaved 3 end of primary transcript 5 RNA processing Intron RNA Figure 18.8 A eukaryotic gene and its transcript. Coding segment mRNA G P P P AAA  AAA 3 Start codon Stop codon 5 Cap 5 UTR 3 UTR Poly-A tail

RNA Processing Animation: RNA Processing © 2011 Pearson Education, Inc.

Primary RNA transcript Figure 18.13 Exons DNA 1 2 3 4 5 Troponin T gene Primary RNA transcript 1 2 3 4 5 Figure 18.13 Alternative RNA splicing of the troponin T gene. RNA splicing mRNA or 1 2 3 5 1 2 4 5

Proteasome and ubiquitin to be recycled Ubiquitin Figure 18.14 Proteasome and ubiquitin to be recycled Ubiquitin Proteasome Protein to be degraded Ubiquitinated protein Protein fragments (peptides) Protein entering a proteasome Figure 18.14 Degradation of a protein by a proteasome.

© 2011 Pearson Education, Inc. Noncoding RNA Only a small fraction of DNA codes for proteins, and a very small fraction of the non-protein-coding DNA consists of genes for RNA such as rRNA and tRNA Significant amount  noncoding RNAs (ncRNAs) © 2011 Pearson Education, Inc.

Effects on mRNAs by MicroRNAs and Small Interfering RNAs MicroRNAs (miRNAs) degrade mRNA or block its translation © 2011 Pearson Education, Inc.

(a) Primary miRNA transcript miRNA miRNA- protein complex Figure 18.15 Hairpin Hydrogen bond miRNA Dicer 5 3 (a) Primary miRNA transcript miRNA miRNA- protein complex Figure 18.15 Regulation of gene expression by miRNAs. mRNA degraded Translation blocked (b) Generation and function of miRNAs

© 2011 Pearson Education, Inc. RNA interference (RNAi) Inhibition of gene expression © 2011 Pearson Education, Inc.

Differential gene expression  leads to different cell types Fertilized egg   many different cell types Gene expression orchestrates development © 2011 Pearson Education, Inc.

(a) Fertilized eggs of a frog (b) Newly hatched tadpole Figure 18.16 Figure 18.16 From fertilized egg to animal: What a difference four days makes. 1 mm 2 mm (a) Fertilized eggs of a frog (b) Newly hatched tadpole

(a) Fertilized eggs of a frog Figure 18.16a Figure 18.16 From fertilized egg to animal: What a difference four days makes. 1 mm (a) Fertilized eggs of a frog

(b) Newly hatched tadpole Figure 18.16b Figure 18.16 From fertilized egg to animal: What a difference four days makes. 2 mm (b) Newly hatched tadpole

© 2011 Pearson Education, Inc. Cell differentiation is the process by which cells become specialized in structure and function The physical processes that give an organism its shape constitute morphogenesis Differential gene expression results from genes being regulated differently in each cell type © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Induction  signal molecules from embryonic cells cause transcriptional changes in nearby target cells differentiation of specialized cell types Animation: Cell Signaling © 2011 Pearson Education, Inc.

(b) Induction by nearby cells Figure 18.17b (b) Induction by nearby cells Early embryo (32 cells) NUCLEUS Signal transduction pathway Figure 18.17 Sources of developmental information for the early embryo. Signal receptor Signaling molecule (inducer)

© 2011 Pearson Education, Inc. Pattern Formation Development of a spatial organization of tissues and organs © 2011 Pearson Education, Inc.

Egg developing within ovarian follicle Nucleus Figure 18.19 Head Thorax Abdomen Follicle cell 1 Egg developing within ovarian follicle Nucleus Egg 0.5 mm Nurse cell Dorsal Right 2 Unfertilized egg Egg shell BODY AXES Anterior Posterior Depleted nurse cells Left Ventral Fertilization (a) Adult Laying of egg 3 Fertilized egg Embryonic development Figure 18.19 Key developmental events in the life cycle of Drosophila. 4 Segmented embryo 0.1 mm Body segments Hatching 5 Larval stage (b) Development from egg to larva

Head Thorax Abdomen 0.5 mm Dorsal Right BODY AXES Anterior Posterior Figure 18.19a Head Thorax Abdomen 0.5 mm Dorsal Right BODY AXES Anterior Posterior Figure 18.19 Key developmental events in the life cycle of Drosophila. Left Ventral (a) Adult

1 2 3 4 5 Follicle cell Egg developing within ovarian follicle Nucleus Figure 18.19b Follicle cell 1 Egg developing within ovarian follicle Nucleus Egg Nurse cell 2 Unfertilized egg Egg shell Depleted nurse cells Fertilization Laying of egg 3 Fertilized egg Embryonic development Figure 18.19 Key developmental events in the life cycle of Drosophila. 4 Segmented embryo 0.1 mm Body segments Hatching 5 Larval stage (b) Development from egg to larva

Genetic Analysis of Early Development: Scientific Inquiry Edward B. Lewis, Christiane Nüsslein-Volhard, and Eric Wieschaus (1995 Nobel Prize)  decoding pattern formation in Drosophila Homeotic genes control pattern formation © 2011 Pearson Education, Inc.

Eye Antenna Wild type Figure 18.20a Figure 18.20 Abnormal pattern formation in Drosophila. Antenna Wild type

Figure 18.20b Leg Figure 18.20 Abnormal pattern formation in Drosophila. Mutant

Cancer results from genetic changes that affect cell cycle control The gene regulation systems that go wrong during cancer are the very same systems involved in embryonic development © 2011 Pearson Education, Inc.

Types of Genes Associated with Cancer Cancer can be caused by mutations to genes that regulate cell growth and division Tumor viruses can cause cancer in animals including humans © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Oncogenes are cancer-causing genes Proto-oncogenes are the corresponding normal cellular genes that are responsible for normal cell growth and division © 2011 Pearson Education, Inc.

within a control element Figure 18.23 Proto-oncogene DNA Translocation or transposition: gene moved to new locus, under new controls Gene amplification: multiple copies of the gene Point mutation: within a control element within the gene New promoter Oncogene Oncogene Figure 18.23 Genetic changes that can turn proto-oncogenes into oncogenes. Normal growth- stimulating protein in excess Normal growth-stimulating protein in excess Normal growth- stimulating protein in excess Hyperactive or degradation- resistant protein

Tumor-Suppressor Genes Tumor-suppressor genes help prevent uncontrolled cell growth © 2011 Pearson Education, Inc.

Figure 18.24 Signaling pathways that regulate cell division. Growth factor MUTATION 2 Protein kinases Ras Hyperactive Ras protein (product of oncogene) issues signals on its own. MUTATION 3 G protein GTP Defective or missing transcription factor, such as p53, cannot activate transcription. Ras P P P P GTP UV light 3 Active form of p53 P P 2 4 Receptor Protein kinases (phosphorylation cascade) 1 DNA damage in genome DNA NUCLEUS 5 Transcription factor (activator) Protein that inhibits the cell cycle DNA Gene expression (b) Cell cycle–inhibiting pathway Protein that stimulates the cell cycle EFFECTS OF MUTATIONS Figure 18.24 Signaling pathways that regulate cell division. Protein overexpressed Protein absent (a) Cell cycle–stimulating pathway Cell cycle overstimulated Increased cell division Cell cycle not inhibited (c) Effects of mutations

Protein kinases (phosphorylation cascade) Receptor Figure 18.24a 1 Growth factor MUTATION Ras Hyperactive Ras protein (product of oncogene) issues signals on its own. 3 G protein GTP Ras P P P P GTP P P 4 2 Protein kinases (phosphorylation cascade) Receptor NUCLEUS 5 Transcription factor (activator) DNA Figure 18.24 Signaling pathways that regulate cell division. Gene expression Protein that stimulates the cell cycle (a) Cell cycle–stimulating pathway

Protein that inhibits the cell cycle Figure 18.24b 2 Protein kinases MUTATION Defective or missing transcription factor, such as p53, cannot activate transcription. 3 UV light Active form of p53 1 DNA damage in genome DNA Figure 18.24 Signaling pathways that regulate cell division. Protein that inhibits the cell cycle (b) Cell cycle–inhibiting pathway

Protein overexpressed Protein absent Figure 18.24c EFFECTS OF MUTATIONS Protein overexpressed Protein absent Cell cycle overstimulated Increased cell division Cell cycle not inhibited Figure 18.24 Signaling pathways that regulate cell division. (c) Effects of mutations

The Multistep Model of Cancer Development © 2011 Pearson Education, Inc.

Loss of tumor- suppressor gene APC (or other) 4 Figure 18.25 Colon 1 Loss of tumor- suppressor gene APC (or other) 4 Loss of tumor- suppressor gene p53 2 Activation of ras oncogene 3 Loss of tumor- suppressor gene DCC Additional mutations 5 Colon wall Figure 18.25 A multistep model for the development of colorectal cancer. Normal colon epithelial cells Small benign growth (polyp) Larger benign growth (adenoma) Malignant tumor (carcinoma)