BIOL 142 Study Guide - Final Guide: Tata Box, Regulatory Sequence, Repressor
9 May 2018
School
Department
Course
Professor
Prokaryotic*Gene*Regulation*
!
Enzyme/element!!
Promote!transcription!!
Inhibit!transcription!!
!
Two!proteins!needed!to!use!lactose:!
- Galactoside+permease!–!transports!lactose!into!the!cell!
o Controlled!by!gene!lacY!
- β-Galactosidase+(B-gal)!–!breaks!down!lactose!inside!the!cell!into!glucose!and!galactose!
o Controlled!by!gene!lacZ!
o X-Gal!–!looks!like!lactose,!is!a!dimer!composed!of!X!(lactose-lookalike)!and!
galactose!
§ B-Gal!cleaves!the!linkage!between!X!and!galactose,!leaving!blue!
precipitate!XX!
!
Lac!genes!normal!and!mutant!functions!
- lacZ!
o Normal:!codes!for!B-gal!
o Mutant:!lacks!functional!B-gal,!cells!can’t!cleave!lactose!
- lacY!
o Normal:!codes!for!galactoside!permease!
o Mutant:!lacks!galactoside!permease,!cells!can’t!accumulate!lactose!or!transport!
lactose!into!the!cell!
- lacI!
o Normal:!repressor!of!lac!operon!(negative!control)!
o Mutant:!produce!B-gal!and!galactoside!permease!even!in!the!absence!of!lactose!
!
Regulatory!elements!
- RNA+polymerase!binds!to!the!promoter!to!transcribe!mRNA!
- Repressor!binds!to!operator!to!prevent!transcription!
o Prevents!RNA!polymerase!from!transcribing!
- Inducer!binds!to!repressor!to!activate!transcription!
o Causes!repressor!to!become!inactive!and!release!from!the!operator!
o Ends!negative!control!of!the!operon!
Document Summary
Galactoside permease transports lactose into the cell: controlled by gene lacy. -galactosidase (b-gal) breaks down lactose inside the cell into glucose and galactose: controlled by gene lacz, x-gal looks like lactose, is a dimer composed of x (lactose-lookalike) and galactose. B-gal cleaves the linkage between x and galactose, leaving blue precipitate xx. Repressor binds to operator to prevent transcription: prevents rna polymerase from transcribing. Inducer binds to repressor to activate transcription: causes repressor to become inactive and release from the operator, ends negative control of the operon. Glucose inhibits lactose transport activity of galactoside permease. Repressor remains bound to the operator because lactose does not accumulate in the cell. Glucose inhibits transcription by decreasing cap activity: already have atp from glucose, don"t need camp. Cap must bind to camp in order to bind to dna. Adenylyl cyclase produces camp from atp and is inhibited by glucose.
