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Third mRNA base (3 end of codon) First mRNA base (5 end of codon) Fig. 17-5 Second mRNA base the mechanism of translation Amino acids Polypeptide Ribosome tRNA with amino acid attached tRNA Anticodon Codons 5 mRNA 3 Fig. 18-3a trp operon Promoter Promoter Genes of operon DNA trpR Regulatory gene mRNA Protein 5 trpE 3 Operator Start codon mRNA 5 RNA polymerase Inactive repressor (a) Tryptophan absent, repressor inactive, operon on E trpD trpC trpB trpA B A Stop codon D C Polypeptide subunits that make up enzymes for tryptophan synthesis Fig. 18-2 Precursor trpE gene Enzyme 1 trpD gene Enzyme 2 trpC gene trpB gene Enzyme 3 trpA gene Tryptophan (a) Regulation of enzyme activity (b) Regulation of enzyme production Fig. 18-3a trp operon Promoter Promoter Genes of operon DNA trpR Regulatory gene mRNA Protein 5 trpE 3 Operator Start codon mRNA 5 RNA polymerase Trp repressor (a) Tryptophan absent, repressor inactive, operon on E trpD trpC trpB trpA B A Stop codon D C Polypeptide subunits that make up enzymes for tryptophan synthesis Fig. 18-3b-2 DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off The actual structure of the Trp Repressor Fig. 18-4b The lac operon lac operon DNA lacZ lacI 3 mRNA 5 mRNA 5 -Galactosidase Allolactose (inducer) lacA RNA polymerase Protein Lac Repressor lacY Inactive repressor (b) Lactose present, repressor inactive, operon on Permease Transacetylase Fig. 18-4a Regulatory gene Promoter Operator lacI DNA lacZ No RNA made 3 mRNA 5 Protein RNA polymerase Active repressor (a) Lactose absent, repressor active, operon off Fig. 18-4b lac operon DNA lacZ lacI 3 mRNA 5 lacA RNA polymerase mRNA 5 -Galactosidase Protein Allolactose (inducer) lacY Inactive repressor (b) Lactose present, repressor inactive, operon on Permease Transacetylase Fig. 18-5 Promoter Operator DNA lacI lacZ CAP-binding site RNA polymerase binds and transcribes Active CAP cAMP Inactive CAP Inactive lac repressor Allolactose (a) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter DNA Operator lacI CAP-binding site Inactive CAP lacZ RNA polymerase less likely to bind Inactive lac repressor (b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized Fig. 18-5 Promoter Operator DNA lacI lacZ CAP-binding site RNA polymerase binds and transcribes Active CAP cAMP Inactive CAP Inactive lac repressor Allolactose (a) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter DNA Operator lacI CAP-binding site Inactive CAP lacZ RNA polymerase less likely to bind Inactive lac repressor (b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification Levels of gene regulation in eukaryotes 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 Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification Levels of gene regulation in eukaryotes DNA Gene available for transcription Gene Transcription - Trancriptional activation in eukaryotes RNA Exon Primary transcript Intron RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Fig. 18-8-1 A Eukaryotic Gene Enhancer (distal control elements) Poly-A signal sequence Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Promoter Downstream Fig. 18-9-1 Activators Promoter DNA Enhancer Distal control element TATA box Gene Fig. 18-9-2 Promoter Activators DNA Enhancer Distal control element Gene TATA box General transcription factors DNA-bending protein Group of mediator proteins Fig. 18-9-3 Promoter Activators DNA Enhancer Distal control element Gene TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II RNA polymerase II Transcription initiation complex RNA synthesis Fig. 18-10 Enhancer Control elements Promoter Albumin gene Crystallin gene LIVER CELL NUCLEUS LENS CELL NUCLEUS Available activators Available activators Albumin gene not expressed Albumin gene expressed Crystallin gene not expressed (a) Liver cell Crystallin gene expressed (b) Lens cell Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification Levels of gene regulation in eukaryotes DNA Gene available for transcription Gene Transcription - Eukaryotes can control the availability of DNA for expression by altering the extent of DNA packing RNA Exon Primary transcript Intron RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Fig. 16-21a Nucleosome (10 nm in diameter) DNA helix in diameter) double (2 nm H1 Histones DNA, the double helix Histones Histone tail Nucleosomes, or “beads on a string” (10-nm fiber) Figure 18.7 Histone tails Amino acids available for chemical modification DNA double helix Nucleosome (end view) (a) Histone tails protrude outward from a nucleosome Acetylated histones Unacetylated histones (b) Acetylation of histone tails promotes loose chromatin structure that permits transcription Fig. Fig.15-18 18-7 Paternal chromosome Normal Igf2 allele is expressed Maternal chromosome Normal Igf2 allele is not expressed (a) Homozygote DNA doubleIgf2 helix Mutant allele inherited from mother Histone tails Wild-type mouse (normal size) Amino acids available for chemical modification Mutant Igf2 allele inherited from father (a) Histone tails protrude outward from a nucleosome Normal size mouse Dwarf mouse (wild type) Normal Igf2 allele is expressed Unacetylated histones (mutant) Mutant Igf2 allele is expressed Acetylated histones Mutant Igf2 allele Normal Igf2 allele is not expressed is not expressed (b) Acetylation of histone tails promotes loose chromatin structure that permits transcription (b) Heterozygotes Fig. 15-8 X chromosomes Early embryo: Two cell populations in adult cat: Active X Allele for orange fur Allele for black fur Cell division and X chromosome inactivation Active X Inactive X Black fur Orange fur Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification Levels of gene regulation in eukaryotes DNA Gene available for transcription Gene Transcription -Alternative splicing can be generated RNA Exon Primary transcript Intron RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Fig. 18-11 Alternative splicing Exons DNA Troponin T gene Primary RNA transcript RNA splicing mRNA or The DSCAM gene (Drosophila): ~38,000 possible splice variants Fig. 18-6 Signal NUCLEUS Chromatin Chromatin modification Levels of gene regulation in eukaryotes DNA Gene available for transcription Gene Transcription - Proteins can be selectively degraded RNA Exon Primary transcript Intron RNA processing Tail Cap mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Degradation of mRNA Translation Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Fig. 18-12 Ubiquitin ligase Ubiquitin Proteasome Protein to be degraded Ubiquitinated protein Proteasome and ubiquitin to be recycled Protein entering a proteasome Protein fragments (peptides) Fig. 12-17b Degraded cyclin G2 checkpoint Cyclin is degraded MPF Cdk Cyclin (b) Molecular mechanisms that help regulate the cell cycle Cyclin accumulation Cdk Fig. 12-6d Metaphase Anaphase Metaphase plate Spindle Centrosome at one spindle pole Telophase and Cytokinesis Cleavage furrow Daughter chromosomes Nuclear envelope forming Nucleolus forming Fig. 18-6 Signal Levels of gene regulation in eukaryotes NUCLEUS Chromatin Chromatin modification Small, non-coding RNAs can affect gene regulation at multiple levels 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 Polypeptide Protein processing Active protein Degradation of protein Transport to cellular destination Cellular function Nematodes with a GFP transgene Nematodes with a GFP transgene Treated with GFP dsRNA dsRNA can reduce gene expression for generations Fig. 18-13 Hairpin miRNA Hydrogen bond Dicer miRNA 5 3 (a) Primary miRNA transcript mRNA degraded miRNAprotein complex Translation blocked (b) Generation and function of miRNAs Fig. 18-13 Hairpin miRNA Hydrogen bond Dicer miRNA 5 3 (a) Primary miRNA transcript mRNA degraded miRNAprotein complex Translation blocked (b) Generation and function of miRNAs
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