1. Two ways to Regulate a Metabolic Pathway

2. Control of Metabolism in Prokaryotes and Eukarotes
Two major ways to control metabolism
Allosteric control of Enzyme activity: negative feedback and feedback inhibition
A quick short-term response
E E E 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 _________________________

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.

4. 2. Regulation of Gene Expression (Eukaryotes)
Much more complex in Eukaryotes than in Prokaryotes!
Some mechanisms include..
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
Transcriptions factors  activate or inhibit transcription
e.g. p53 protein is a transcription factor
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”
E E E E 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. Control of Gene Expression in Prokaryotes
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

10. The lac operon: regulated synthesis of inducible enzymes

11. The lac operon: regulated synthesis of inducible enzymes

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. ALE 11. Question 7 on Page 11 Mutation
Effect of mutation on lac operon when
Allolactose present
Allolactose 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

16. Figure 18.10 A hypothesis to explain how prions propagate

17. Figure 18.11 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 18.12 Detecting genetic recombination in bacteria

23. Figure 18.13 Transduction (Layer 1)

24. Figure 18.13 Transduction (Layer 2)

25. Figure 18.13 Transduction (Layer 3)

26. Figure 18.13 Transduction (Layer 4)

27. Figure 18.14 Bacterial mating

28. Figure 18.15 Conjugation and recombination in E. coli (Layer 1)

29. Figure 18.15 Conjugation and recombination in E. coli (Layer 2)

30. Figure 18.15 Conjugation and recombination in E. coli (Layer 3)

31. Figure 18.15 Conjugation and recombination in E. coli (Layer 4)

32. Figure 18.16 Insertion sequences, the simplest transposons

33. Figure 18.17 Insertion of a transposon and creation of direct repeats

34. Figure 18.18 Anatomy of a composite transposon

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