CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 15 Regulation of Gene Expression

© 2014 Pearson Education, Inc. Figure 15.1

© 2014 Pearson Education, Inc. Figure 15.2 Regulation of gene expression Precursor trpE gene (a) Regulation of enzyme activity Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 Tryptophan (b) Regulation of enzyme production trpD gene trpC gene trpB gene trpA gene

© 2014 Pearson Education, Inc. Operons: The Basic Concept  Operon – section of DNA that includes the operator, the promoter, and the  operator - regulatory “switch” usually positioned within the promoter  operon can be switched off by a protein repressor which binds to the operator and blocking RNA polymerase

© 2014 Pearson Education, Inc.  A corepressor molecule cooperates with a repressor protein to switch an operon off

© 2014 Pearson Education, Inc. Figure 15.3 Promoter trp operon Genes of operon DNA Regulatory gene mRNA Protein RNA polymerase Inactive repressor Operator Start codon Stop codon mRNA 5 trpEtrpDtrpC trpB trpA EDCBA (a) Tryptophan absent, repressor inactive, operon on DNA mRNA Protein Active repressor No RNA made Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off Polypeptide subunits that make up enzymes for tryptophan synthesis 5 3 trpR

© 2014 Pearson Education, Inc. Repressible and Inducible Operons: Two Types of Negative Gene Regulation  A repressible operon is usually on; binding of a repressor shuts off transcription  An inducible operon is usually off; an inducer molecule inactivates the repressor and turns on transcription

© 2014 Pearson Education, Inc. Figure 15.4 DNA mRNA Promoter Operator Regulatory gene No RNA made RNA polymerase 3 5 IacZ Active repressor Protein (a) Lactose absent, repressor active, operon off IacZ IacY IacA Iac I DNA mRNA Protein RNA polymerase Inactive repressor Allolactose (inducer) (b) Lactose present, repressor inactive, operon on mRNA lac operon lac I PermeaseTransacetylase  -Galactosidase

© 2014 Pearson Education, Inc. Concept 15.2: Eukaryotic gene expression is regulated at many stages  Eukaryotic gene expression is regulated at many stages

© 2014 Pearson Education, Inc. Figure 15.6 Signal NUCLEUS Chromatin Chromatin modification: DNA unpacking involving histone acetylation and DNA demethylation DNA Gene RNAExon Gene available for transcription Transcription Primary transcript Intron RNA processing Tail mRNA in nucleus Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Translation Degradation of mRNA Polypeptide Cap Protein processing, such as cleavage and chemical modification Active protein Transport to cellular destination Degradation of protein Cellular function (such as enzymatic activity, structural support)

© 2014 Pearson Education, Inc. Regulation of Chromatin Structure  The structural organization of chromatin helps regulate gene expression  Genes within highly condensed chromatin are usually not expressed  The location of a promoter relative to histones can influence gene transcription

© 2014 Pearson Education, Inc. Histone Modifications and DNA Methylation  histone acetylation, loosens chromatin, promoting transcription  Methylation condenses chromatin and inhibits transcription

© 2014 Pearson Education, Inc. Figure 15.7 Nucleosome Unacetylated histones Acetylated histones Histone tails

© 2014 Pearson Education, Inc. Epigenetic Inheritance  chromatin modifications do not alter DNA sequence, but may be passed to future generations of cells  epigenetic inheritance - inheritance of traits by mechanisms not directly involving DNA sequence

© 2014 Pearson Education, Inc. Figure 15.8 DNA Upstream Enhancer (distal control elements) Proximal control elements Transcription start site ExonIntron Exon Promoter IntronExon Poly-A signal sequence Transcription termination region Down- stream Transcription Exon Intron Exon Poly-A signal Primary RNA transcript (pre-mRNA) 5 Cleaved 3 end of primary transcript Intron RNA mRNA RNA processing Coding segment CapUTR Start codon Stop codon UTR Poly-A tail G PP P AAA  AAA

© 2014 Pearson Education, Inc.  Proximal control elements are located close to the promoter  Enhancers are Distal control elements, Enhancers and Specific Transcription Factors

© 2014 Pearson Education, Inc.  Activator protein binds to enhancer and stimulates transcription

© 2014 Pearson Education, Inc. Figure 15.9 Activation domain DNA DNA-binding domain

© 2014 Pearson Education, Inc. Figure 15.UN01 Chromatin modification Transcription RNA processing TranslationmRNA degradation Protein processing and degradation

© 2014 Pearson Education, Inc. Figure DNA Enhancer Distal control element Activators Promoter Gene TATA box

© 2014 Pearson Education, Inc. Figure DNA Enhancer Distal control element Activators Promoter Gene TATA box DNA- bending protein Group of mediator proteins General transcription factors

© 2014 Pearson Education, Inc. Figure DNA Enhancer Distal control element Activators Promoter Gene TATA box DNA- bending protein Group of mediator proteins General transcription factors RNA polymerase II RNA synthesis Transcription initiation complex

© 2014 Pearson Education, Inc. RNA Processing  alternative RNA splicing - different mRNA’s produced from the same primary transcript, (depends on which segments are treated as exons and which as introns) Animation: RNA Processing

© 2014 Pearson Education, Inc. Figure 15.UN02 Chromatin modification Transcription RNA processing Translation mRNA degradation Protein processing and degradation

© 2014 Pearson Education, Inc. Figure DNA Primary RNA transcript mRNA or Exons Troponin T gene RNA splicing

© 2014 Pearson Education, Inc. mRNA Degradation  mRNA Degradation - sequences that influence mRNA life span are at the 3 end

© 2014 Pearson Education, Inc. Initiation of Translation  The initiation of translation can be blocked by regulatory proteins that bind to the mRNA

© 2014 Pearson Education, Inc. Protein Processing and Degradation  protein processing, including cleavage and chemical modification, are subject to control

© 2014 Pearson Education, Inc. Concept 15.3: Noncoding RNAs play multiple roles in controlling gene expression  A significant amount of the genome may be transcribed into noncoding RNAs (ncRNAs)  Noncoding RNAs regulate gene expression at several points

© 2014 Pearson Education, Inc. Effects on mRNAs by MicroRNAs and Small Interfering RNAs  MicroRNAs (miRNAs) - small single-stranded RNA’s that bind to complementary mRNA sequences to degrade the mRNA or block translation

© 2014 Pearson Education, Inc. Figure 15.UN03 Chromatin modification Transcription RNA processing Translation mRNA degradation Protein processing and degradation

© 2014 Pearson Education, Inc. Figure miRNA miRNA- protein complex Translation blockedmRNA degraded The miRNA binds to a target mRNA. 1 If bases are completely complementary, mRNA is degraded. If match is less than complete, translation is blocked. 2

© 2014 Pearson Education, Inc.  small interfering RNAs (siRNAs) are similar to miRNAs but form from different RNA precursors  gene expression by siRNAs is called RNA interference (RNAi)

© 2014 Pearson Education, Inc. Making cDNA (complimentary DNA) for genetic studies and genetic engineering Fig. 16-5, p.245