Fig. 18-1 Figure 18.1 What regulates the precise pattern of expression of different genes?

(a) Regulation of enzyme activity (b) Regulation of enzyme production
Fig. 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

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 mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

Polypeptide subunits that make up enzymes for tryptophan synthesis
Fig. 18-3a 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 Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes (a) Tryptophan absent, repressor inactive, operon on

(b) Tryptophan present, repressor active, operon off
Fig. 18-3b-1 DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes (b) Tryptophan present, repressor active, operon off

(b) Tryptophan present, repressor active, operon off
Fig. 18-3b-2 DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes (b) Tryptophan present, repressor active, operon off

(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

(a) Lactose absent, repressor active, operon off
Fig. 18-4a Regulatory gene Promoter Operator 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

(b) Lactose present, repressor inactive, operon on
Fig. 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 Allolactose (inducer) Inactive repressor (b) Lactose present, repressor inactive, operon on

(a) Lactose present, glucose scarce (cAMP level
Fig. 18-5 Promoter Operator DNA lacI lacZ CAP-binding site RNA polymerase binds and transcribes Active CAP cAMP Inactive lac repressor Inactive CAP Allolactose (a) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter Operator DNA lacI lacZ Figure 18.5 Positive control of the lac operon by catabolite activator protein (CAP) CAP-binding site RNA polymerase less likely to bind Inactive CAP Inactive lac repressor (b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized

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

(a) Histone tails protrude outward from a nucleosome
Fig. 18-7 Histone tails Amino acids available for chemical modification DNA double helix (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

(distal control elements)
Fig Poly-A signal sequence Enhancer (distal control elements) Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Downstream Promoter Figure 18.8 A eukaryotic gene and its transcript

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

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

Promoter Activators Gene DNA Enhancer
Fig Promoter Activators Gene DNA Distal control element Enhancer TATA box Figure 18.9 A model for the action of enhancers and transcription activators

Fig Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins Figure 18.9 A model for the action of enhancers and transcription activators

Fig Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II Figure 18.9 A model for the action of enhancers and transcription activators RNA polymerase II Transcription initiation complex RNA synthesis

Enhancer Promoter Albumin gene Control elements Crystallin gene
Fig Enhancer Promoter Albumin gene Control elements Crystallin gene LIVER CELL NUCLEUS LENS CELL NUCLEUS Available activators Available activators Albumin gene not expressed Figure Cell type–specific transcription Albumin gene expressed Crystallin gene not expressed Crystallin gene expressed (a) Liver cell (b) Lens cell

Exons DNA Troponin T gene Primary RNA transcript RNA splicing mRNA or
Fig Exons DNA Troponin T gene Primary RNA transcript Figure Alternative RNA splicing of the troponin T gene RNA splicing mRNA or

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

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

(a) Fertilized eggs of a frog (b) Newly hatched tadpole
Fig Figure From fertilized egg to animal: What a difference four days makes (a) Fertilized eggs of a frog (b) Newly hatched tadpole

(a) Fertilized eggs of a frog
Fig a Figure From fertilized egg to animal: What a difference four days makes (a) Fertilized eggs of a frog

(b) Newly hatched tadpole
Fig b Figure From fertilized egg to animal: What a difference four days makes (b) Newly hatched tadpole

(b) Induction by nearby cells
Fig Unfertilized egg cell Sperm Nucleus Fertilization Two different cytoplasmic determinants NUCLEUS Early embryo (32 cells) Zygote Signal transduction pathway Mitotic cell division Signal receptor Figure Sources of developmental information for the early embryo Two-celled embryo Signal molecule (inducer) (a) Cytoplasmic determinants in the egg (b) Induction by nearby cells

(a) Cytoplasmic determinants in the egg
Fig a Unfertilized egg cell Sperm Nucleus Fertilization Two different cytoplasmic determinants Zygote Mitotic cell division Figure Sources of developmental information for the early embryo Two-celled embryo (a) Cytoplasmic determinants in the egg

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

Master regulatory gene myoD Other muscle-specific genes
Fig Nucleus Master regulatory gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF Figure Determination and differentiation of muscle cells

MyoD protein (transcription Myoblast factor) (determined) Nucleus
Fig Nucleus Master regulatory gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF mRNA OFF MyoD protein (transcription factor) Myoblast (determined) Figure Determination and differentiation of muscle cells

(fully differentiated cell)
Fig Nucleus Master regulatory gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF mRNA OFF MyoD protein (transcription factor) Myoblast (determined) Figure Determination and differentiation of muscle cells mRNA mRNA mRNA mRNA Myosin, other muscle proteins, and cell cycle– blocking proteins MyoD Another transcription factor Part of a muscle fiber (fully differentiated cell)

Figure 18.17 Key developmental events in the life cycle of Drosophila
Head Thorax Abdomen 0.5 mm Dorsal Right BODY AXES Anterior Posterior Left Ventral (a) Adult Follicle cell 1 Egg cell developing within ovarian follicle Nucleus Egg cell Nurse cell 2 Unfertilized egg Egg shell Depleted nurse cells Fertilization Laying of egg 3 Fertilized egg Figure Key developmental events in the life cycle of Drosophila Embryonic development 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
Fig a Head Thorax Abdomen 0.5 mm Dorsal Right BODY AXES Anterior Posterior Figure Key developmental events in the life cycle of Drosophila Left Ventral (a) Adult

(b) Development from egg to larva
Fig b Follicle cell 1 Egg cell developing within ovarian follicle Nucleus Egg cell Nurse cell 2 Unfertilized egg Egg shell Depleted nurse cells Fertilization Laying of egg 3 Fertilized egg Embryonic development Figure 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

Eye Leg Antenna Wild type Mutant Fig. 18-18
Figure Abnormal pattern formation in Drosophila Wild type Mutant

Eye Antenna Wild type Fig. 18-18a
Figure Abnormal pattern formation in Drosophila Antenna Wild type

Fig b Figure Abnormal pattern formation in Drosophila Leg Mutant

Fig EXPERIMENT Tail Head T1 T2 A8 T3 A7 A1 A2 A3 A4 A5 A6 Wild-type larva Tail Tail A8 A8 A7 A6 A7 Mutant larva (bicoid) RESULTS Figure Is Bicoid a morphogen that determines the anterior end of a fruit fly? Fertilization, translation of bicoid mRNA 100 µm Anterior end Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo CONCLUSION Nurse cells Egg bicoid mRNA Developing egg Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo

EXPERIMENT Tail Head Wild-type larva Tail Tail Mutant larva (bicoid)
Fig a EXPERIMENT Tail Head A8 T1 T2 T3 A7 A1 A6 A2 A3 A4 A5 Wild-type larva Tail Tail Figure Is Bicoid a morphogen that determines the anterior end of a fruit fly? A8 A8 A7 A7 A6 Mutant larva (bicoid)

RESULTS Anterior end Bicoid mRNA in mature unfertilized egg
Fig b RESULTS Fertilization, translation of bicoid mRNA 100 µm Anterior end Figure Is Bicoid a morphogen that determines the anterior end of a fruit fly? Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo

CONCLUSION Nurse cells Egg bicoid mRNA Developing egg
Fig c CONCLUSION Nurse cells Egg bicoid mRNA Developing egg Figure Is Bicoid a morphogen that determines the anterior end of a fruit fly? Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo

within a control element within the gene
Fig Proto-oncogene DNA Translocation or transposition: Gene amplification: Point mutation: within a control element within the gene New promoter Oncogene Oncogene Figure 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

Figure 18.21 Signaling pathways that regulate cell division
Growth factor MUTATION Hyperactive Ras protein (product of oncogene) issues signals on its own Ras 3 G protein GTP Ras GTP 2 Receptor 4 Protein kinases (phosphorylation cascade) NUCLEUS 5 Transcription factor (activator) DNA Gene expression Protein that stimulates the cell cycle (a) Cell cycle–stimulating pathway 2 Protein kinases MUTATION Defective or missing transcription factor, such as p53, cannot activate UV light 3 Active form of p53 1 DNA damage in genome Figure Signaling pathways that regulate cell division DNA Protein that inhibits the cell cycle (b) Cell cycle–inhibiting pathway EFFECTS OF MUTATIONS Protein overexpressed Protein absent Cell cycle overstimulated Increased cell division Cell cycle not inhibited (c) Effects of mutations

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

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

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

EFFECTS OF MUTATIONS Fig. 18-22
Colon EFFECTS OF MUTATIONS Loss of tumor- suppressor gene APC (or other) 1 Activation of ras oncogene 2 Loss of tumor-suppressor gene p53 4 Colon wall Loss of tumor-suppressor gene DCC 3 Additional mutations 5 Figure A multistep model for the development of colorectal cancer Normal colon epithelial cells Small benign growth (polyp) Larger benign growth (adenoma) Malignant tumor (carcinoma)

Colon Colon wall Normal colon epithelial cells Fig. 18-22a
Figure A multistep model for the development of colorectal cancer Normal colon epithelial cells

1 Small benign growth (polyp) Loss of tumor- suppressor gene
Fig b Loss of tumor- suppressor gene APC (or other) 1 Small benign growth (polyp) Figure A multistep model for the development of colorectal cancer

Activation of ras oncogene 2 3 Larger benign growth (adenoma) Loss of
Fig c Activation of ras oncogene 2 Loss of tumor-suppressor gene DCC 3 Larger benign growth (adenoma) Figure A multistep model for the development of colorectal cancer

Additional mutations Malignant tumor (carcinoma) Loss of 4
Fig d Loss of tumor-suppressor gene p53 4 Additional mutations 5 Malignant tumor (carcinoma) Figure A multistep model for the development of colorectal cancer

Fig Figure Tracking the molecular basis of breast cancer

Operon Promoter Genes A B C Operator RNA polymerase A B C Polypeptides
Fig. 18-UN1 Operon Promoter Genes A B C Operator RNA polymerase Fig. 18-UN1 A B C Polypeptides

no corepressor present Corepressor
Fig. 18-UN2 Genes expressed Genes not expressed Promoter Genes Operator Active repressor: corepressor bound Inactive repressor: no corepressor present Corepressor Fig. 18-UN2

Genes not expressed Genes expressed Promoter Operator Genes
Fig. 18-UN3 Genes not expressed Genes expressed Promoter Operator Genes Fig. 18-UN2 Active repressor: no inducer present Inactive repressor: inducer bound Fig. 18-UN3

Protein processing and degradation
Fig. 18-UN4 Chromatin modification Transcription • Genes in highly compacted chromatin are generally not transcribed. • Regulation of transcription initiation: DNA control elements bind specific transcription factors. • Histone acetylation seems to loosen chromatin structure, enhancing transcription. Bending of the DNA enables activators to contact proteins at the promoter, initiating transcription. • DNA methylation generally reduces transcription. • Coordinate regulation: Enhancer for liver-specific genes Enhancer for lens-specific genes Chromatin modification Transcription RNA processing • Alternative RNA splicing: RNA processing Primary RNA transcript mRNA degradation Translation mRNA or Fig. 18-UN4 Protein processing and degradation Translation • Initiation of translation can be controlled via regulation of initiation factors. mRNA degradation • Each mRNA has a characteristic life span, determined in part by sequences in the 5 and 3 UTRs. Protein processing and degradation • Protein processing and degradation by proteasomes are subject to regulation.

Chromatin modification
Fig. 18-UN5 Chromatin modification • Small RNAs can promote the formation of heterochromatin in certain regions, blocking transcription. Chromatin modification Transcription Translation RNA processing • miRNA or siRNA can block the translation of specific mRNAs. mRNA degradation Translation Protein processing and degradation Fig. 18-UN5 mRNA degradation • miRNA or siRNA can target specific mRNAs for destruction.

Enhancer Promoter Gene 1 Gene 2 Gene 3 Gene 4 Gene 5
Fig. 18-UN6 Enhancer Promoter Gene 1 Gene 2 Gene 3 Fig. 18-UN6 Gene 4 Gene 5

Fig. 18-UN7 Fig. 18-UN7

Fig. 18-UN8 Fig. 18-UN8

You should now be able to:
Explain the concept of an operon and the function of the operator, repressor, and corepressor Explain the adaptive advantage of grouping bacterial genes into an operon Explain how repressible and inducible operons differ and how those differences reflect differences in the pathways they control

Explain how DNA methylation and histone acetylation affect chromatin structure and the regulation of transcription Define control elements and explain how they influence transcription Explain the role of promoters, enhancers, activators, and repressors in transcription control

Explain how eukaryotic genes can be coordinately expressed
Describe the roles played by small RNAs on gene expression Explain why determination precedes differentiation Describe two sources of information that instruct a cell to express genes at the appropriate time

Explain how maternal effect genes affect polarity and development in Drosophila embryos
Explain how mutations in tumor-suppressor genes can contribute to cancer Describe the effects of mutations to the p53 and ras genes

Fig. 18-1 Figure 18.1 What regulates the precise pattern of expression of different genes?

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Fig. 18-1 Figure 18.1 What regulates the precise pattern of expression of different genes?

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