1. Controlling Gene Expression 7.4

2. Control Mechanisms housekeeping genes code for proteins that are needed all the time; they are constantly being transcribed and translated not all proteins are needed by all cells at all times, so gene regulation is important to an organism's survival

3. Prokaryotic Cells use operons to control gene expression an operon is: –a promoter region –an operator –a cluster of genes

5. Lactose disaccharide found in milk or milk sugars intestinal bacteria cells metabolize lactose for energy

6. lac operon 3 genes control the proteins needed to metabolize lactose the lac operon contains: –a promoter –an operator –3 genes: lacZ, lacY, and lacA

7. lac operon animation Narrated animation: http://highered.mheducation.com/sites/dl/f ree/0072835125/126997/animation27.ht ml

9. lac operon if no lactose is present, the genes do not need to be expressed, and lacI (a repressor protein) is bound to the operator if lactose is present, it binds to lacI and inactivates it, allowing the genes to be expressed lactose is an inducer

10. Tryptophan a non-essential amino acid used for protein synthesis intestinal bacteria cells can obtain tryptophan from a mammalian diet, or they can synthesize it themselves

11. trp operon 5 genes control the biosynthesis of tryptophan the trp operon contains: –a promoter –an operator –5 genes

12. trp operon animation Narrated animation: http://highered.mheducation.com/olcweb/ cgi/pluginpop.cgi?it=swf::535::535::/site s/dl/free/0072437316/120080/bio26.swf: :The%20Tryptophan%20Repressor

14. trp operon if no tryptophan is present, the genes need to be expressed and the trp repressor protein is inactive

15. trp operon if tryptophan is present, the genes do not need to be expressed; tryptophan binds to the trp repressor protein, which binds to the operator tryptophan is a corepressor

16. Summary The lac operon is inducible. The trp operon is repressible.

17. Eukaryotic Cells genes can be regulated: during transcription (most common) after transcription during translation after translation

18. Transcriptional promoters must be accessible in order for transcription to occur –chromatin remodelling –addition of acetyl group (CH 3 COO - ) to histones transcription initiation complex regulated by activators & repressors

19. Transcriptional methylation of genes –methyl group attached to cytosine in promoter region –causes gene to be inactive

20. Agouti Mice

21. Post-Transcriptional alternative splicing binding of masking proteins to mRNA (common in unfertilized egg cells) changes in rate of degradation of mRNA (e.g. casein in rat mammary gland cells)

22. Translational changes in length of poly(A) tail can increase or decrease the length of time for translation (not fully understood)

23. Post-Translational processing mechanisms (e.g., removal of specific sections activates certain proteins such as insulin) chemical modification (addition or deletion of chemical groups) addition or removal of tags to control rate of degradation of proteins

24. Cancer

25. Cancerous cells genes that regulate cell growth can become oncogenes, causing unregulated cell division high concentrations of telomerase cause constant lengthening of telomeres