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Two ways to Regulate a Metabolic Pathway. Control of Metabolism in Prokaryotes and Eukarotes Two major ways to control metabolism 1.Allosteric control.

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Presentation on theme: "Two ways to Regulate a Metabolic Pathway. Control of Metabolism in Prokaryotes and Eukarotes Two major ways to control metabolism 1.Allosteric control."— Presentation transcript:

1 Two ways to Regulate a Metabolic Pathway

2 Control of Metabolism in Prokaryotes and Eukarotes Two major ways to control metabolism 1.Allosteric control of Enzyme activity: negative feedback and feedback inhibition A quick short-term response E 1 E 2 E 3 E 4 A  B  C  D  Product Recall the role played by PFK (PhosphoFructoKinase) in the Allosteric control of glycolysis –PFK Activated by _________________________ –PFK Inhibited by _________________________

3 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 needed

4 2. 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 factor 3.Chemical modification of DNA (e.g. DNA methylation) —Permanently inactivates genes

5 The trp operon: a repressible operon Anabolic Pathway for Tryptophan Synthesis from Precursor Molecule “A” E1 E2 E3 E4 E5 A  B  C  D  E  Tryptophan

6 Control of Gene Expression in Prokaryotes Vocabulary 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 operon

7 The trp operon: regulated synthesis of repressible enzymes (Layer 1)

8 The trp operon: regulated synthesis of repressible enzymes (Layer 2)

9 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 transcribed Control of Gene Expression in Prokaryotes

10 The lac operon: regulated synthesis of inducible enzymes

11

12 cAMP Receptor Protein (CRP) Lac Operon Transcribed only if Lactose is present in the absence of Glucose

13 Lac Operon is not transcribed if glucose is present

14 cAMP (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 Transcribed

15 Mutation Effect of mutation on lac operon when Allolactose presentAllolactose absent Mutation of regulatory gene: Repressor will not bind to allolactose Mutation of operator: Repressor will not bind to operator Mutation of regulatory gene:Repressor will not bind to operator Mutation of promoter: RNA polymerase will not bind to promoter It 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 11

16 Figure A hypothesis to explain how prions propagate

17 Figure Replication of the bacterial chromosome

18 Figure 18.x7 E. coli

19 Figure 18.x8 E. coli dividing

20 Figure 18.x9 Bacterium releasing DNA with plasmids

21 Figure 18.x10 Plasmids

22 Figure Detecting genetic recombination in bacteria

23 Figure Transduction (Layer 1)

24 Figure Transduction (Layer 2)

25 Figure Transduction (Layer 3)

26 Figure Transduction (Layer 4)

27 Figure Bacterial mating

28 Figure Conjugation and recombination in E. coli (Layer 1)

29 Figure Conjugation and recombination in E. coli (Layer 2)

30 Figure Conjugation and recombination in E. coli (Layer 3)

31 Figure Conjugation and recombination in E. coli (Layer 4)

32 Figure Insertion sequences, the simplest transposons

33 Figure Insertion of a transposon and creation of direct repeats

34 Figure Anatomy of a composite transposon

35 Unnumbered Figure (page 353) Bacterial and viral growth curves


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