GENE EXPRESSION

1. GENE EXPRESSION • First genes must become AVAILABLE for expression. There are ROAD BLOCKS to becoming available. • Exs. • Does the cell have the needed DNA sequence? • Physical state: RNA is only transcribed when the nucleus is in interphase and chromatin is less condensed. When chromatin is highly folded, it’s unable to be expressed (therefore, it’s “unavailable”).

2. MORE ROADBLOCKS c) Are there repetitive sequences? The more of the these, the better the chance of being expressed d) mRNA must be processed before leaving the nucleus-if not processed it may not reach a ribosome where translation occurs e) Enhancers? Were enhancers available to increase the chance that the promoter was found? f) Were introns weeded out?

3. Even more roadblocks g) Did amplification occur? The more copies of the code, the better chance of expression h) Chromosome w/ “expression unit” could’ve been ditched during embryonic development—therefore NO expression i) Methylation? Highly methylated means decreased expression j) Did RNA polymerase find transcription factor way back in the beginning? k) Did transcription factor find its enhancer sequence? *Enhancer helps TF help RNA polymerase find the promoter.

4. Still more roadblocks… L) Some mRNA’s don’t live very long—longer life means more proteins are produced m) After the protein is made, it must be changed and moved before finally being expressed…did this happen? Were the proper groups added to the sides? Did the protein even reach its target?

5. Gene expression: Finding the perfect prom outfit…rdblks? • It’s Feb. You see the perfect dress in a catalog. • You order it. • The person on the phone writes down the wrong catalog #. • You get size 10 in red. You wanted size 8 in blue. • You return it. • They misunderstand you. You now have size 8 in purple.

6. 7) You return this one. 8) You now have size 8 in blue. Yea! 9) It’s March. Now to get the shoes dyed… 10) Your dress is Carribean Blue. Your shoes came back Duke Blue. 11) They try again. 12) Now they are Carolina Blue. 13) They try again. 14) A perfect match! Yea! 15) Now the jewelry. 

7. 16) You go to 10 different stores looking for those dangling diamond/sapphire earrings that you’d seen last year. Each store says, “So and so down the mall has EXACTLY what you’re looking for…” 17) Finally the very last store has them. 18) Before you can get your hands on them, someone else has HER hands on them. The store says it will express mail you your very own set. YEA!

8. 19) Your earrings arrive via UPS on the very day of the prom. Your entire outfit is now AVAILABLE for expression. BUT do you make it to the prom to be seen/expressed??? Stay tuned….

9. Your boyfriend…a roadblock? • Your boyfriend’s car breaks down. • He borrows his cousin’s car, but the cousin says, “Dude, it’s trashed..you gotta wash it.” • On the way to the prom, you REALLY do give out of gas. • You finally get to Angus Barn, but there’s a 45 min wait (and you HAD reservations…Gov. Perdue has a party there and SHE takes PRIORITY!)

10. 5) On the way to Nash Tech and the Prom site…there’s only one lane of 64 available…workers are expanding it… 6) Finally at 10:00, you and your beau make it to the prom and you are TRULY EXPRESSED!

11. operonexs.- “non-reality” *** “GAME” OPERON: The goal of the GAME operon: code for genes which code for enzymes that let you watch football on TV on Sundays. No football on TV, the game operon is OFF. Football game is on TV, the game operon has to turn on.

12. repressor • What does the repressor do if there is no football game on TV? The repressor “clamps” on and you just fall asleep on the couch.

13. INDUCER • Your “NFLogical” clock just knows when it’s time for the pregame show, so you wake up and watch the game. This inducer keeps you awake until the game is over and you “sleep” until time for another game.

14. Back to REALITY: The LAC OPERON • The goal of the lac operon is to code for 3 genes which code for 3 proteins/enzymes involved in lactose metabolism. • No lactose in the body, the lac operon has to turn OFF. • Lactose is in the body, the lac operon has to turn ON.

15. REPRESSOR • If there is no lactose in the body, the repressor clamps on to the promoter, thus blocking the binding of the RNA polymerase, which therefore blocks transcription.

16. INDUCER • In this case, allolactose (an isomer of lactose) binds to the repressor. This causes it to change its shape, so now it won’t “fit” onto the promoter. So, RNA polymerase can…not transcription can occur! This makes sense because you’re transcribing genes for lactose metabolism…no need to transcribe those genes if there was no lactose to metabolize.

17. SO… • The INDUCER keeps blocking the REPRESSOR until all the lactose is broken down. Then the REPRESSOR represses again…

18. The MOP OPERON • Situation: Woman A is a CLEAN FREAK. She has 2 children who love to scatter toys and books throughout her house. • Explain when the MOP OPERON is on. • Explain when the MOP OPERON is off. • What are the REPRESSORS? • What are the INDUCERS?

19. The shop operon • Situation: Woman B loves to SPEND MONEY. She spends and spends because her $$$$ “burns a hole in her pocket”. She spends until she has no more to spend (then she works!). • Explain when her SHOP OPERON is on. • Explain when her SHOP OPERON is off. • What are the repressors? • What are the inducers?