Regulation of Gene Expression

1. Regulation of GeneExpression Sec. 6.4 (p.267)

2. Control Mechanisms 42,000 genes code for proteins in Humans Are the proteins for all of these genes being made all the time??

3. No! Why?? Gene Regulation • Proteins are needed at certain times (E.g. Hormones and proteins) • Do the islets of langerhans continually produce insulin? What would happen if genes were expressed all the time?

4. If genes were always expressed, theywould always make protein. Example: Insulin • Insulin is only required in cells with high glucose levels . • Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle. • If we produce too much insulin then too much glucose is taken out of the blood and you get low blood sugar.

5. Transcription Factors Genes can be turned “on” or “off” by proteins that switch on genes by binding to DNA. • In turn, they help RNA polymerase to bind RNA Polym-erase RNA Polymerase can't find the promoter. promotor RNA Polym-erase transcription factors act like flags for RNA Polymerase, helping it to find the promoter promotor

6. Certain Transcription Factors bind to specific regions on the DNA. What do you think are the functions of the following transcription Factor Types and DNA sequences? Which ones do you think pair up and bind together? Transcription Factor DNA Sequence Activator Silencer Repressor Enhancer Basal Level Transcription Factors TATA Box

7. Types of Transcription Factors

8. House Keeping Genes(AKA: Constitutive genes) • Genes are turned ‘ON’ all the time –not regulated. • Vital to an organism’s life • Examples??

9. Four Levels of Control • The extent to which they are transcribed is regulated (transcriptional and posttranscriptional) • The extent to which they are translated is regulated (translationaland postranslational)

10. Gene Regulation: Operons Gene regulation mechanisms in prokaryotes Operon: A cluster of genes grouped together under the control of one promotor. • Each operon contains a promoter, operator and genes

11. General Structure Definitions The operon consists of: Promoter • a section of DNA where RNA polymerase binds Operator • a section of DNA that interacts with the repressor protein to alter transcription Regulatory genes • code for the repressor protein Structural genes • code for the target proteins

12. Lactose • Type of Macromolecule? • Lactose makes up around 2-8% of the solids in milk • Consists of Glucose and Galactose

13. Lactose Intolerance Undigested lactose remains in the gut and bacteria feed on it, causing the typical symptoms: - stomach cramps - nausea - bloating - acid reflux - flatulence Can't digest lactose because don't have enough lactase

14. lacOperon Produces B-galactosidase - enzyme that breaks down lactose - remember: lactase breaks down lactose and B- galactosidase degrades it - produced after lactose has been ingested (therefore when lactose levels are high) Inducible operon: lactose present induces transcription

18. trpOperon Produces tryptophan - A non-essential amino acid - Produced when none has been ingested (when tryptophan levels are low) Trpoperon is normally active, unless a repressor turns it off.

22. How is regulation in Eukaryotes different? • See pg 269-270 • Read section 6.4 & try question25,27,28,29 pg 269, • Pg 272 questions;

23. Gene Regulation in Eukaryotes Histones and nucleosomes keep DNA tightly wrapped transcription factors mRNA modification RNA interference Protein modification of shape or ubiquitin tag 5 levels of control pre-transcriptional transcriptional post-transcriptional translational post-translational

24. Eukaryotic gene control • Genes are not organized into operons • They require a much more elaborate control • Ie. many activators, and enhancer regions on DNA to regulate gene control under certain conditions. Pg 270

25. Homework • More review if needed • Page 267-272 #2-8