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  1. Announcements • Homework for Chapter 7 Part 3 due Friday • If you have VUU sponsored event-turn it in by email (scan it...via Genius Scan App) • If you aren’t in class to get the homework…download it from MyVUU or class website. You are expected to turn it in by the due date. • Remember, lab 4 is tomorrow • No online quiz because it was due days ago • For the key to homework for Chapter 7 Part 1, check class website and MyVUU • ( • Class Instagram: vuubio201 • Class Facebook: Vuu Microbiology

  2. Chapter 7, Part 3:The Blueprint of Life, from DNA to Protein

  3. Question Now that we know how a bacteria goes from a gene encoded in the DNA to actually expressing it, do you think bacteria want to make all gene products (i.e. proteins) all the time? Why or why not? NO! WASTE OF ENERGY! WHY MAKE IT IF YOU DON’T NEED IT?

  4. Question At what step(s) do you think genes are controlled? Hint: Do you want to make the mRNA if you are not going to need the gene product (protein)? Answer: transcriptional control Why make the mRNA if you are never going to make the gene product?

  5. To understand how transcription is controlled, we have to know how genes are organized in bacteria.

  6. Gene Structure: Monocistronic vs. Polycistronic (Cistron=Gene) • Monocistronic: • 1 promoter directs the synthesis of 1 mRNA that can be translated into 1 protein • Polycistronic: • 1 promoter can direct the synthesis of 1 mRNA that can be translated into more than 1 protein • Bacteria can have both monocistronic and polycistronic genes Monocistronic DNA 1 Polycistronic DNA 2 Terminator Start Site/Promoter Terminator Start Site/Promoter

  7. More Gene Structure Groupings • Operon: Set of regulated genes transcribed as a single polycistronic message • Regulon: Separate operons controlled by a single regulator DNA 1 Polycistronic Start Site/Promoter Terminator DNA Start Site/Promoter Terminator Start Site/Promoter Terminator

  8. Enzyme Classification • Enzymes (i.e. gene products/proteins) are constantly made=constitutive • Example: Metabolic enzymes • Enzymes not constantly made but can be produced when needed=inducible • Example: Enzymes made during starvation • Enzymes made routinely but their synthesis can be turned off=repressible • Example: Enzymes in amino acid synthesis

  9. Controlling Transcription • 2 methods to control transcription • Alternative Sigma Factors: • Review: Standard sigma factors (part of RNA polymerase) recognize promoters that need to be routinely expressed • Alternative: Recognize different promoters for genes not routinely expresses • DNA binding proteins: bind to DNA and influence transcription • Repressors (negative regulation) • 2 mechanisms to work • Activators (positive regulation) Alternative Standard

  10. Controlling Transcription With Repressors

  11. Controlling Transcription with Activators

  12. The Lac Operon: Example of Gene Regulation • What is the purpose of the Lac operon? • Encodes proteins involved in lactose transport and degradation • LacZ-cleaves lactose into glucose and galactose • LacY-permease that pumps lactose out of cell • LacA-function unknown • **ONLY EXPRESSED UNDER LOW GLUCOSE**

  13. The Lac Operon: How It Works

  14. But Wait… What happens to the lac operon when glucose is high? But, how does the lac operon get turned on in low glucose? High glucose=No lac operon expression! How? Answer, NEXT SLIDE!

  15. QUESTION: Is the lac operon under positive, negative, or both regulation? Both! How do you know? Controlled by activator and repressor!

  16. Why Do Bacteria Use Glucose Over Lactose? • Glucose is a very efficient carbon source; it can enter directly into the metabolic paths that provide both energy and substrates for making more complex compounds • Lactose as the carbon sourcemust first be broken down into the two component sugars before it can be used

  17. Now That We Know Bacteria Gene Expression, How Does It Differ From Eukaryotes?

  18. Questions/Muddiest Points Write them down and leave them at the front of the room!