1. Gene regulation

2. Gene expression models  Prokaryotes and Eukaryotes employ common and different methods of gene regulation  Prokaryotic models 1. Trp operon 2. Lac operon  Eukaryotic concept 1. Transcription factors

3. Anabolic tryptophan pathway http://highered.mheducation.com/sites/0072995246/student_view0/chapter7/the_trp_operon.html  Tryptophan is an amino acid that must be made by E. coli through an anabolic pathway involving several enzymes  The trp operon encodes these enzymes Operon - a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter.

4. Trp operon  The trp operon consists of 5 genes

5. Trp operon  Upstream of these genes is the promoter region (eg. TATA box)  Within the promoter is a sequence called the operator

6. Trp operon  A protein called repressor is able to bind the operator when conditions are correct

7. In the absence of Trp  Without tryptophan, the repressor protein cannot bind the operator

8. In the absence of Trp  With nothing in its way, RNA polymerase is free to initiate transcription

9. In the absence of Trp  With nothing in its way, RNA polymerase is free to initiate transcription  This transcript will be translated into the enzymes capable of making tryptophan

10. In the absence of Trp  With nothing in its way, RNA polymerase is free to initiate transcription  This transcript will be translated and the cell will begin making Trp

11. In the presence of Trp  When Trp is present it is able to bind to inactive repressor protein

12. In the presence of Trp  When Trp is present it is able to bind to inactive repressor protein

13. In the presence of Trp  The repressor is now able to bind to the operator

14. In the presence of Trp  The repressor is now able to bind to the operator  This blocks RNA polymerase from transcribing the trp genes and the cell does not make Trp

15. Catabolic lactose pathway http://highered.mheducation.com/sites/0072995246/student_view0/chapter7/the_lac_operon.html  Lactose is used by E. coli in the absence of glucose, its favourite carbohydrate food source  The enzymes responsible for breaking down lactose are under the influence of the lac operon

16. lac operon  The lac operon is a bit more complicated and involves a gene that is outside the operon

17. lac operon  The lac operon itself contains 5 genes but control over it is exerted by a regulatory gene called lacI

18. In the absence of lactose  lacI encodes the lac repressor protein and is always transcribed/translated into its active form

19. In the absence of lactose  The active repressor protein blocks transcription of the genes that encode enzymes for lactose metabolism

20. In the presence of lactose  When E. coli has lactose available,  -galactosidase converts it into allolactose

21. In the presence of lactose  When E. coli has lactose available,  -galactosidase converts it into allolactose  Allolactose binds the repressor protein and inactivates it

22. In the presence of lactose  With the repressor out of the way, RNA polymerase is free to do it’s job and transcribe the genes for lactose metabolising enzymes

23. In the presence of lactose  With the repressor out of the way, RNA polymerase is free to do it’s job and transcribe the genes for lactose metabolising enzymes

24. In the presence of lactose  With the repressor out of the way, RNA polymerase is free to do it’s job and transcribe the genes for lactose metabolising enzymes  http://highered.mheducation.com/sites/0072995246/student_view0/chapt er7/the_lac_operon__induction.html

25. Eukaryotic gene expression  Eukaryotic gene regulation is similar to that in prokaryotes in that…  …protein-DNA interactions occur  But there are complicating factors such as…  …far more proteins are involved  …DNA is densely packed as chromatin

26. Transcription factors  Protein that bind to specific DNA sequences andcontrol their rate of transcription are called transcription factors  eg. trp repressor and lac repressor  In eukaryotes transcription is naturally repressed by DNA packaging  Transcription factors bind to promoter sites to keep DNA available to RNA polymerase for transcription  Often numerous transcription factors are involved  Read pg. 312 – 313 to learn about the complexity of eukaryotic gene regulation