(distal control elements) Fig. 18-8-1 A Eukaryotic Gene Poly-A signal sequence Enhancer (distal control elements) Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Downstream Promoter

(distal control elements) Fig. 18-8-2 Poly-A signal sequence Enhancer (distal 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

(distal control elements) Fig. 18-8-3 Poly-A signal sequence Enhancer (distal 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 Coding segment mRNA 3 Start codon Stop codon 5 Cap 5 UTR 3 UTR Poly-A tail

RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2 Fig. 17-11-3 RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2 Protein Other proteins snRNA snRNPs Spliceosome 5 Spliceosome components Cut-out intron mRNA 5 Exon 1 Exon 2

Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription Fig. 17-12 Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Domain 3 Domain 2 Domain 1 Polypeptide

Table 21-1

(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 Enzyme 3 trpA gene Tryptophan Tryptophan (a) Regulation of enzyme activity (b) Regulation of enzyme production

(a) Regulation of enzyme activity (b) Regulation of enzyme production Fig. 18-2 Precursor trpE gene Enzyme 1 trpD gene Regulation of gene expression Enzyme 2 trpC gene trpB gene Enzyme 3 trpA gene Tryptophan (a) Regulation of enzyme activity (b) Regulation of enzyme production

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

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 (a) Tryptophan absent, repressor inactive, operon on

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 Trp repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on

(b) Tryptophan present, repressor active, operon off 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

The lac operon Lac Repressor lac operon DNA lacI lacZ lacY lacA RNA Fig. 18-4b The lac operon lac operon DNA lacI lacZ lacY lacA RNA polymerase 3 mRNA mRNA 5 5 -Galactosidase Permease Transacetylase Protein Lac Repressor 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 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 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

(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 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

Levels of gene regulation in eukaryotes 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

Levels of gene regulation in eukaryotes 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

(distal control elements) Fig. 18-8-1 A Eukaryotic Gene Poly-A signal sequence Enhancer (distal control elements) Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Downstream Promoter

Promoter Activators Gene DNA Enhancer Fig. 18-9-1 Promoter Activators Gene DNA Distal control element Enhancer TATA box

Promoter Activators Gene DNA Enhancer Fig. 18-9-2 Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins

Promoter Activators Gene DNA Enhancer Fig. 18-9-3 Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II RNA polymerase II Transcription initiation complex RNA synthesis

Enhancer Promoter Albumin gene Control elements Crystallin gene Fig. 18-10 Enhancer Promoter Albumin gene Control elements Crystallin gene LIVER CELL NUCLEUS LENS CELL NUCLEUS Available activators Available activators Albumin gene not expressed Albumin gene expressed Crystallin gene not expressed Crystallin gene expressed (a) Liver cell (b) Lens cell

Levels of gene regulation in eukaryotes 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

Nucleosomes, or “beads on a string” (10-nm fiber) Fig. 16-21a Nucleosome (10 nm in diameter) DNA double helix (2 nm in diameter) H1 Histone tail Histones DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)

(a) Histone tails protrude outward from a nucleosome Fig. 15-18 Fig. 18-7 Normal Igf2 allele is expressed Paternal chromosome Maternal chromosome Histone tails Normal Igf2 allele is not expressed Wild-type mouse (normal size) Amino acids available for chemical modification (a) Homozygote DNA double helix Mutant Igf2 allele inherited from mother Mutant Igf2 allele inherited from father (a) Histone tails protrude outward from a nucleosome Normal size mouse (wild type) Dwarf mouse (mutant) Normal Igf2 allele is expressed Mutant Igf2 allele is expressed Unacetylated histones Acetylated histones Mutant Igf2 allele is not expressed Normal Igf2 allele is not expressed (b) Acetylation of histone tails promotes loose chromatin structure that permits transcription (b) Heterozygotes

X chromosomes Allele for orange fur Early embryo: Allele for black fur Fig. 15-8 X chromosomes Allele for orange fur Early embryo: Allele for black fur Cell division and X chromosome inactivation Two cell populations in adult cat: Active X Inactive X Active X Black fur Orange fur