Presentation on theme: "Study Guide/Outline—Bacterial Gene Regulation Bacterial Gene Regulation What is an operon? How is it different from a eukaryotic gene? In the lac operon,"— Presentation transcript:
Study Guide/Outline—Bacterial Gene Regulation Bacterial Gene Regulation What is an operon? How is it different from a eukaryotic gene? In the lac operon, what cellular or environmental conditions must exist in order for the (WT) lac operon to express its genes? How do these environmental conditions positively or negatively regulate the operon? What are the different parts, and their functions, of the operon? How do mutations in “upstream” parts of the operon (promoter, operator, coding genes) affect the “downstream” areas of the operon? How do missense and nonsense mutations have different results? The lacI gene is not part of the Lac Operon. How is the lac I gene involved with the Lac operon? What kinds of mutations are cis-dominant? Trans-dominant? Constitutive ON? Constitutive-OFF? How can a bacteria be a partial diploid? How does being diploid for the LacI gene create complexities in the regulation of the Lac Operon?
Brooker Figure Incubate the cells long enough to allow lac operon induction. 5. Burst the cells with a sonicator. This allows β-galactosidase to escape from the cells. – Lactose F’ F In mero-zygote strain, the lac I + gene on the F´ factor makes enough repressor to bind to both operator sites (restoring WT phenotype on main chromosome). Lactose is taken up, is converted to allolactose, and removes the repressor Lactose 3. + Lactose 4. Z+Z+ I–I– P O Y+Y+ A+A+ Z+Z+ P O Y+Y+ I+I+ Experimental levelConceptual level 1. Grow mutant strain and merozygote strain separately. 2.Divide each strain into two tubes. 3. In one of the two tubes, add lactose. Mutant strain Merozygote strain Merozygote – Lactose Mutant F′ Operon is constitutive-on in Mutant strain because no repressor is made Lactose 2. Z+Z+ I–I– P O Y+Y+ A+A+ Z+Z+ I–I– P O Y+Y+ A+A+ Z+Z+ P O Y+Y+ A+A+ I+I+ Z+Z+ I–I– P O Y + A+A+ Z + I – P O Y + A + A+A+ Z+Z+ I–I– P O Y+Y+ A+A+ Z+Z+ P O Y+Y+ I+I+
Question Will a loss-of-function mutation in P lac (promoter sequence) be cis-dominant or trans-dominant?
Lactose status (assume absence of Glucose) GenotypePromoter Seq RepressorOperator Seq Lac Z Lac Y Lac A Type of mutation (e.g. cis- dominant, consititutive ON) AbsentWT + Active Bound No Expression none PresentWT + InactivatedOpenWT B-Gal WT Permease WT Transacet. none PresentLac Y miss PresentLac Z Nons PresentP Lac(-) AbsentLac O c PresentLac O c
Lactose status (assume absence of Glucose) Genotype Promoter Seq Repressor Operator Seq Lac ZLacY Lac A Type of mutation (e.g. cis- dominant) AbsentLac I (-) Absent F’-Lac I (+) Lac I (-) Absent F’-LacO c Lac O+ Present F’-LacO c Lac O+