Two ways to Regulate a Metabolic PathwayControl of Metabolism in Prokaryotes and Eukarotes2. Regulation of Gene Expression (Prokaryotes)2. Regulation of Gene Expression (Eukaryotes)The trp operon: a repressible operonControl of Gene Expression in ProkaryotesThe trp operon: regulated synthesis of repressible enzymes (Layer 1)The trp operon: regulated synthesis of repressible enzymes (Layer 2)Slide 9The lac operon: regulated synthesis of inducible enzymesSlide 11cAMP Receptor Protein (CRP) Lac Operon Transcribed only if Lactose is present in the absence of GlucoseLac Operon is not transcribed if glucose is presentSlide 14ALE 11. Question 7 on Page 11Figure 18.10 A hypothesis to explain how prions propagateFigure 18.11 Replication of the bacterial chromosomeFigure 18.x7 E. coliFigure 18.x8 E. coli dividingFigure 18.x9 Bacterium releasing DNA with plasmidsFigure 18.x10 PlasmidsFigure 18.12 Detecting genetic recombination in bacteriaFigure 18.13 Transduction (Layer 1)Figure 18.13 Transduction (Layer 2)Figure 18.13 Transduction (Layer 3)Figure 18.13 Transduction (Layer 4)Figure 18.14 Bacterial matingFigure 18.15 Conjugation and recombination in E. coli (Layer 1)Figure 18.15 Conjugation and recombination in E. coli (Layer 2)Figure 18.15 Conjugation and recombination in E. coli (Layer 3)Figure 18.15 Conjugation and recombination in E. coli (Layer 4)Figure 18.16 Insertion sequences, the simplest transposonsFigure 18.17 Insertion of a transposon and creation of direct repeatsFigure 18.18 Anatomy of a composite transposonUnnumbered Figure (page 353) Bacterial and viral growth curvesTwo ways to Regulate a Metabolic PathwayControl of Metabolism in Prokaryotes and EukarotesTwo major ways to control metabolism1. Allosteric control of Enzyme activity: negative feedback and feedback inhibition•A quick short-term response E1 E2 E3 E4•A  B  C  D  Product•Recall the role played by PFK (PhosphoFructoKinase) in the Allosteric control of glycolysis–PFK Activated by _________________________ –PFK Inhibited by _________________________2. Regulation of Gene Expression (Prokaryotes)•Anabolic Pathways (e.g. tryptophan synthesis)—Product accumulation inhibits the transcription (mRNA synthesis) of genes coding for the enzymes needed to make the product.–Enzymes are not made unless they are needed•Catabolic Pathways (e.g. lactose breakdown)— Presence of substrate activates the transcription (mRNA synthesis) of genes coding for the enzymes needed to breakdown the substrate.—Enzymes are not made unless they are needed2. Regulation of Gene Expression (Eukaryotes)Much more complex in Eukaryotes than in Prokaryotes! Some mechanisms include..1. Accessibility of genes  condensed (coiled) DNA prevents transcription  RNA polymerase can’t access the promoter—e.g. Barr bodies: One X chromosome is inactivated in females by producing a tightly-wound structure called a Barr body 2. Transcriptions factors  activate or inhibit transcription—e.g. p53 protein is a transcription factor3. Chemical modification of DNA (e.g. DNA methylation)—Permanently inactivates genesThe trp operon: a repressible operonAnabolic Pathway for Tryptophan Synthesis from Precursor Molecule “A” E1 E2 E3 E4 E5 A  B  C  D  E  TryptophanControl of Gene Expression in ProkaryotesVocabulary •Operon: Regulated cluster of structural genes that have a common function (e.g. lac Operon, trp Operon)—Structural genes code for mRNA —Advantage of an Operon?•Promoter: Site on where RNA polymerase binds to DNA•Operator: Controls access of RNA polymerase to structural genes—Acts as an “on/off” switch for transcription—Located between promoter and operonThe trp operon: regulated synthesis of repressible enzymes (Layer 1)The trp operon: regulated synthesis of repressible enzymes (Layer 2)Vocabulary (continued) •Repressor—Protein that binds reversibly to operator—Binding to operator blocks the transcription of the operon•Co-repressor (involved with repressible (anabolic) operons—e.g. trp operon)—Molecule that binds reversibly repressor protein —Co-repressor binding activates the repressor—Co-repressor-repressor complex binds to operator  operon not transcribedControl of Gene Expression in ProkaryotesThe lac operon: regulated synthesis of inducible enzymesThe lac operon: regulated synthesis of inducible enzymescAMP Receptor Protein (CRP) Lac Operon Transcribed only if Lactose is present in the absence of GlucoseLac Operon is not transcribed if glucose is presentcAMP (Cyclic AMP): Activates Lac Operon When Lactose is present in the absence of Glucose•Cellular concentrations of cAMP increase as cellular concentration of glucose decrease. •cAMP binds to an inactive CRP (Cyclic AMP Receptor Protein)•cAMP-CRP complex  binds to promoter  Lac Operon TranscribedMutationEffect of mutation on lac operon whenAllolactose present Allolactose absentMutation of regulatory gene: Repressor will not bind to allolactoseMutation of operator: Repressor will not bind to operatorMutation of regulatory gene:Repressor will not bind to operatorMutation of promoter: RNA polymerase will not bind to promoterIt was through the effects of mutations that enabled Jacob and Monod to decipher how the lac operon works. Predict how the following mutations would affect lac operon function in the presence and absence of allolactose. Note: use this question to test your knowledge of the lac operon. Study the how the lac operon works, then attempt this question, using only your cerebral cortex as a reference ALE 11. Question 7 on Page 11Figure 18.10 A hypothesis to explain how prions propagateFigure 18.11 Replication of the bacterial chromosomeFigure 18.x7 E. coliFigure 18.x8 E. coli dividingFigure 18.x9 Bacterium releasing DNA with plasmidsFigure 18.x10 PlasmidsFigure 18.12 Detecting genetic recombination in bacteriaFigure 18.13 Transduction (Layer 1)Figure 18.13 Transduction (Layer 2)Figure 18.13 Transduction (Layer 3)Figure 18.13 Transduction (Layer 4)Figure 18.14 Bacterial matingFigure 18.15 Conjugation and recombination in E. coli (Layer 1)Figure 18.15 Conjugation and recombination in E. coli (Layer 2)Figure 18.15 Conjugation and recombination in E. coli (Layer 3)Figure 18.15 Conjugation and recombination in E. coli (Layer 4)Figure 18.16