Do Now:

1. Do Now: Review: how can you distinguish between pro/eukaryotes? Structurally? Environmentally? Both types of organisms seek efficiency, so genes often can be turned on and off. What kinds of “switches” might control whether genes are on and off for each of these? Do you think they are the same? What about the response? Explain your response.

2. Gene Control Prokaryotes vs. Eukaryotes

3. What kind of environment do bacteria live in? How do you think this impacts the way genes get regulated, if at all? • Quick response needed • Have enough? • New stimuli (food?) introduced Utilize it fast!!! STOP

4. Quick Review in Metabolic regulation • Allosteric inhibitors – provide feedback inhibition (enzyme regulators) • Product of pathwaysignals continuation ofpath to STOP • Making all these enzymes is wasteful

5. Alternative Method… • Gene regulation • Block transcription of genes for ALL enzymes in a pathway,not just enzyme function • Energy efficient

6. More on gene regulation • Turning genes ON & OFF regulates amt of enzymes present in cell • Example: OFF • Enough tryptophan present, bacteria turns off genes coding for enzymes used to build it • Example: ON • Sugar lactose enters cell, genes coding for enzymes to break sugar down turned on

7. The Operon Model • Operon – group of genes with related functions • Genes– code for specific proteins • Promoter– RNA pol binding site • controls transcription of ALL genes in operon • Single mRNA produced • Operator – binding site of repressor protein (turns off gene) These 3 make up an operon!

8. trp RNA polymerase RNA polymerase repressor repressor repressor enzyme1 1 enzyme2 2 enzyme3 3 enzyme4 4 promoter repressor protein operator tryptophan trp trp trp trp trp trp trp trp trp tryptophan – repressor protein complex Ex: Repressible operon: tryptophan • Excess tryptophan present, binds to tryp repressor proteintriggering repressor to bind to DNA • blocks (represses) transcription • tend to be anabolic pathways gene1 gene2 gene3 gene4 TATA DNA mRNA trp conformational change in repressor protein! trp

9. RNA polymerase RNA polymerase repressor repressor repressor enzyme1 1 enzyme2 2 enzyme3 3 enzyme4 4 promoter repressor protein operator lactose lac lac lac lac lac lac lac lactose – repressor protein complex Ex: Inducibleoperon: lactose Lactose present, binds to lac repressor protein & triggers repressor to release DNA • induces transcription • catabolic pathways lac gene1 gene2 gene3 gene4 TATA DNA mRNA lac conformational change in repressor protein! lac

10. What about Eukaryotes? How are they different? What might the process have to accommodate for? How might it do this? • Eukaryotes often multicellular • Must maintain homeostasis • Coordinate body as a whole • Differentiated & specialized cells Battle changing environment

11. When does gene control occur??? • Packing/unpacking DNA • Transcription • mRNA processing • Translation • Protein processing • Protein degradation

12. 1. DNA Packing If all 46 of your chromosomes were lined up in a row, your DNA would be over 3 feet long. How can your cells contain this large amount of material when cells are microscopic? • Coils & Folds • Double helix • Nucleosomes • Chromatin fiber • Looped domains • Chromosomes from DNA double helix to condensed chromosome

13. A little more about nucleosomes… • “Beads on a string” • 1st level of DNA packing • histone proteins • 8 protein molecules • positively charged amino acids • bind tightly to negatively charged DNA

14. Degree of packing regulates transcription • Tightly packed = no transcription = genes OFF • Heterochromatin – “dark” DNA = tight • Euchromatin – “light” DNA = loose

15. Methylation of DNA (adding -CH3’s) blocks transcription factors  no transcription  genes OFF! • Acetylation of histones(adding –COCH3’s) unwinds DNA  coils loosen  transcription  genes ON!

16. 2. Transcription Initiation • Control regions on DNA • Promoter • nearby control sequence – “standard” rate • bind RNA pol • bind transcription factors • Enhancer • distant control sequence – “enhanced” rate • bind activator proteins

17. Transcription complex… Activator Proteins • regulatory proteins bind to DNA at distant enhancer sites • increase the rate of transcription Enhancer Sites regulatory sites on DNA distant from gene Activator Activator Activator Coactivator E F B RNA polymerase II H TFIID A Coding region T A T A Core promoter and initiation complex Initiation Complex at Promoter binding site of RNA pol

18. 3. Post-transcriptional control • Alternate splicing pattern • ↑ variation in protein family

19. 4. Regulation of mRNA degradation • Lifespan of mRNA controls amt of protein synthesized • Review: which component on mRNA determines lifespan? • mRNA can last from hrs to weeks!

20. What if degradation is interfered with??? • Small interfering RNAs (siRNA) • short segments of RNA (21-28 bases) • bind to mRNA • create sections of double-stranded mRNA • “death” tag for mRNA • triggers degradation • gene “silencing” • post-transcriptional control • turns off gene = no protein

21. Action of siRNA dicerenzyme mRNA for translation siRNA double-stranded miRNA + siRNA breakdownenzyme (RISC) mRNA degraded functionally turns gene off

22. 5. Control of Translation • Block initiation of translation • Regulatory proteins attach to 5’ end • Prevent attachment of ribosome & initiator tRNA • Synthesis turned OFF

23. 6/7. Protein Processing & Degradation • Protein processing • Folding, cleaving, adding sugar groups, targeting for transport • Protein degradation • Ubiquitin – (76 aa’s) “death tag” • Proteasome – degradation machinery

24. What Darwin Never Knew… • Video – 39:57