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Gene Expression Ch 11
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Gene expression Genes to proteins
Genotype to phenotype Produce specific proteins when and where they are needed
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lac Operon E. Coli make enzymes to utilize lactose sugars
Dependent on presence/absence of lactose 3 enzymes to take up and metabolize lactose Genes that code for enzymes located next to each other in DNA
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Lactose-utilization genes
Fig. 11-1b OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA mRNA RNA polymerase cannot attach to promoter Active repressor Protein Operon turned off (lactose absent) DNA RNA polymerase bound to promoter mRNA Protein Enzymes for lactose utilization Lactose Inactive repressor Operon turned on (lactose inactivates repressor)
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lac Operon Control sequence Operon Promoter Operator
Genes, promoter and Operator ***Exist almost solely in prokaryotes
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lac Operon Repressors Block RNA polymerase from binding
Regulatory genes code for repressors Located outside the operon
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Lactose-utilization genes
Fig. 11-1b OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA mRNA RNA polymerase cannot attach to promoter Active repressor Protein Operon turned off (lactose absent) DNA RNA polymerase bound to promoter mRNA Protein Enzymes for lactose utilization Lactose Inactive repressor Operon turned on (lactose inactivates repressor)
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Trp Operon trp operon repressor is inactive alone When tryptophan present, binds to repressor, enabling it to switch transcription off
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Promoter Operator Gene DNA Active repressor Active repressor
Fig. 11-1c Promoter Operator Gene DNA Active repressor Active repressor Tryptophan Inactive repressor Inactive repressor Lactose lac operon trp operon
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Differentiation Specialized in structure and function
Results from selective gene expression Variety of cell types, expressing different combination of genes
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Cell division in culture
Differentiation Differentiated cells may retain all of their genetic potential Most differentiated cells retain a complete set of genes Root of carrot plant Root cells cultured in nutrient medium Cell division in culture Plantlet Adult Plant Single cell Figure 11.3
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The Chromosome Packaging helps regulate expression Histone proteins
Aid in packaging and ordering DNA DNA double helix (2-nm diameter) Histones Linker “Beads on a string” Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Supercoil (300-nm diameter) Metaphase chromosome 700 nm TEM
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The Chromosome Nucleosome
DNA-histone complex involving DNA wound around 8 histone protein core Resembles beads on a string Linkers Join consecutive nucleosomes Packing presumably prevents access of transcription proteins DNA double helix (2-nm diameter) Histones Linker “Beads on a string” Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Supercoil (300-nm diameter) Metaphase chromosome 700 nm TEM
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Proteins controlling transcription
Regulatory proteins turn off/on gene transcription Transcription factors Enhancers Silencers RNA splicing Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6
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Proteins controlling transcription
Enhancers Activators bind and bend DNA Interact with other transcription factor proteins Bind as complex to promoter Silencers RNA splicing Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6
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Proteins controlling transcription
Silencers Bind to DNA and inhibit start of transcription Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6
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Splicing Alternate RNA splicing Splicing can occur in more than 1 way
Different mRNA from same RNA transcript DNA RNA transcript mRNA Exons or RNA splicing Figure 11.7
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Small RNA’s miRNA RNA interference 1 Protein miRNA miRNA- protein
complex 2 Target mRNA 4 3 mRNA degraded OR Translation blocked
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Regulation of translation
Breakdown of mRNA Initiation of translation Protein activation Protein breakdown Folding of polypeptide and formation of S—S linkages Cleavage Initial polypeptide (inactive) Folded polypeptide (inactive)
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Cascades Protein products from one set of genes activate another set
Egg cell Egg cell within ovarian follicle Protein signal Protein products from one set of genes activate another set Homeotic gene Follicle cells Gene expression 1 “Head” mRNA Cascades of gene expression 2 Embryo Body segments 3 Gene expression Adult fly 4
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Signal transduction pathways
Signaling cell Signal molecule Series of molecular changes that converts signal on cell surface to specific response inside cell Receptor protein Plasma membrane 1 2 3 Target cell Relay proteins Transcription factor (activated) 4 Nucleus DNA 5 mRNA Transcription New protein 6 Translation Figure 11.14
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Cloning A clone is an individual created by asexual reproduction and thus is genetically identical to a single parent
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Cloning Regeneration Nuclear Transplantation
Reproductive and Therapeutic cloning Remove nucleus from egg cell Add somatic cell from adult donor Grow in culture to produce an early embryo (blastocyst) Implant blastocyst in surrogate mother Remove embryonic stem cells from blastocyst and grow in culture Induce stem cells to form specialized cells (therapeutic cloning) Clone of donor is born (reproductive cloning) Donor cell Nucleus from donor cell Figure 11.10
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Reproductive Cloning Clone grown into new individual Not exact copy
Behavioral differences Ethical questions
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Therapeutic Cloning Medical potential Embryonic stem cells
Adult stem cells Replace non-reproducing specialized cells as needed Only give rise to certain tissues Obtaining differentiated cells for cell replacement therapy Tissue taken from patient, nucleus from one of the cells implanted into donor oocyte without nucleus. Resulting egg is allowed to develop into early embryo and ES cells are harvested and grown and in culture. Induced to differentiate and transplanted to patient.
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Cancer Divide uncontrollably Oncogene
Mutations whose protein products affect the cell cycle Oncogene Can cause cancer when present in a single copy
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Cancer Proto-oncogene Gene that has potential to become oncogene
Mutation or virus Proto-oncogene DNA Mutation within the gene Multiple copies of the gene Gene moved to new DNA locus, under new controls Oncogene New promoter Hyperactive growth- stimulating protein in normal amount Normal growth- stimulating protein in excess Figure 11.16A
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Cancer Tumor-suppressor genes Help prevent uncontrolled growth
Mutated tumor-suppressor gene Normal growth- inhibiting protein Cell division under control Defective, nonfunctioning protein Cell division not under control Figure 11.16B
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Oncogene proteins and faulty tumor-suppressor proteins can interfere with normal signal transduction pathways Growth-inhibiting factor Receptor Nonfunctional transcription factor (product of faulty p53 tumor-suppressor gene) Relay proteins Transcription factor (activated) Transcription Translation Protein that inhibits cell division cannot trigger transcription Protein absent (cell division not inhibited) Normal product of p53 gene Figure 11.17B Growth factor Target cell Receptor Hyperactive relay protein (product of ras oncogene) issues signals on its own Normal product of ras gene Relay proteins Transcription factor (activated) DNA Nucleus Transcription Translation Protein that stimulates cell division Figure 11.17A
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Cancer Series of genetic changes Colon cancer 1 2 3 Colon wall
Increased cell division Oncogene activated 2 Growth of polyp Tumor-suppressor gene inactivated 3 Growth of malignant tumor (carcinoma) Second tumor- suppressor gene inactivated Cellular changes: DNA changes:
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Cancer Series of mutations Chromosomes mutation 1 2 3 4 mutations
Normal cell Malignant cell Figure 11.18B
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Table 11.20
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Videos Lac Operon RNA Splicing
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