MBG Transcription Regulation in Prokaryotes PDF

unit 4 : transcription regulation in prokaryotes What makes * hollow diffrent than a...

unit 4 : transcription regulation in prokaryotes What makes * hollow diffrent than a enzyme come enzymes ↳ having a sigma factor * constitutive and inducible promoters Constitutive ↳ · transcribed at all times and circumstances > - include tRNAs , ribosomal proteins , RNAD ↳ inducible transcribed under certain circumstances · only · these promoters have up and down veguation * regulation of transcription at promoters ↳ repression and or activation regulates promoters · glo promoters > - controlled by both repsesion and activation ES4 · promoters > - controlled only by activation * mechanisms of repression Je restraining in a way I repression via steric hindrance · trp repressor Is relatively weak · lac repressor 2 inhibition of transition to open complex 3 inhibition of promoter clearance ↑ anti activation sigma factor 5 anti * mechanism 1 : tryptophan repressor ↳ consists of a set of structural genes that are expressed as a RNA polysistronic ↳ translated into 5 enzymes that Synthesize tryptophan from chosimic acid · trp E · trpD · trp C · tip B · trpD bit in E controls the. Colivia negitive operon for feed synthasis back loop of Ltryptophan/s function what # happens when tryptophan is absent ? ↳ repressor dimer (aka aporepressor) cannot bind to the operator # what happens when tryptophan binds to aporepressor ? changes the configuration so that I ↳ it it can bind to the. 6 operator thus preventing transcription when this happens the tryptophan is called co-repressor ↳ because it is weak it has attenuation mu another level of control that weakens the "transcription of operon # how does attenuation work ? ↳ by haveing the RNAP Stop before transcription of structural genes but after it started making RNA * mechanism 1 : lac operon What when F is disachride lactose # happens. Coli presented with ? It expresses the ↳ genes that encode enzymes needed to catabolize food ↳ experimental observations in E coli. show regulation of transcription :  lac + culture medium without lactose has · grown in concentrations of Belactosidase in the cell · premase is very low · if lactose is added to last but there is no glucose the number of each molecule folds is 103 higher # in the absance of lactose what happens to repressor Protein ? %↳ it is bound to the operator sequance E prevents transcribing the structural genes RNAP from of operon What does the inducer aka lactose do ? # ↳ it interacts with repressor protein to prevent if from binding to the operator sequance What happens # when the lactose the medium ? Sugar is in ↳ the operon is induced ↳ transcription of polysistronic MRNA coding lack , lacy , lacA begins ↳ functional lac repressor is motetramer a proteincomplex made of 4 subunits · each dimer binds to a specific sequance at -22 and the this results DNA looping · in # what does DNA looping do ? 3 RNAP from to prevents the binding -35 and -10 What happens when # ligand binds to lac repressor ? ↳ the is released from DNA because of repressor an induced conformational change caused by ligand repressor interaction * mechanism 2 : inhibition of transition to open complex ↳ RNAP-O Complex can find to promoter but transition to open complex is blocked Mechanisms : Inhibition * of promoter clearance ↳ transcription bubble can be formed but RNAP Sigma movement is blocked * mechanism 4 : anti activation ↳ repressor molecule is what removes the activator * mechanim 5 : anti sigma factor ↳ the to ability compete for to core prevent RNAP it's coynete Sigma factor 70 J -> definition ↳ is mostly used for sigma factors other than · ex. Sigma factor for sporulation ↳ some bacteriophages use their own antiSigma factors to stop expression of cellular protein * mechanisms of activation regulated recruitment - activation polymerase mechanism * 1 : regulated recruitment ↳ activator extends the binding site for RNAD * catabolite activator protein (CAP) ↳ it activates transcription from more than 150 promoters in E: Coli > # what activates it ? ↳ CAMP [cyclic adenosine monophosphate] # what happens when CAP is activated by CAMP ? ↳ CAD binds to promoter and help RNAP-Sigma to bind too When ↳ CAMP is at low concentrations , CAP is not active ↳ CAP dependent promoters have weak-35 Sequance # how does the affect weak-35 Sequance RNAP-Sigma ? it ↳ is unable to bind to the promoter without CApasistance * models for class) , class II , class III promoter activation Class class 11 * 2Ap binding sites from -62 and -103 * sites the -35 CAPbinding overlap interacts with interacts with aCTD * carboxy / terminal Th, ↓ domain [aCTD] and sigma factor N termina domain class III * requires binding of at least 2 CAP dimers or 1 CApdimer and I regulation specific activator * interactions can be simmilar to class) and 11 promoter , the difference is that each aCTD makes different interactions * activation [positive control] of lac operon by CAP # what is the signal for this pathway ? ↳ the nucleotides 3-5' AMP- CAMP cycilic ↳ CAMP levels are high when glucose levels are low and vice versa What # is the synthasis of cAMP from ATP catalyzed by ? ↳ adenylate cyclase # what is it's breakdown into Amp catalyzed by ? ↳ CAMP phosphodiestrerase CAP site ↳ lac operon has a site called binding What binds to CAP site? # said binding ↳ a protein called catabolite activativ protein ↳ it binds when it is complexed with cAMP ↳ the glucose acts as ATP for bacteria ↳ When both glucose and lactose present and glucose runs out , lactose kicks in how * does CAP-cAMP Stimulate transcription? ↳ mode , I CAP-cAMp interacts with RNAP by to CTD · binding a ↳ model 2 · has increased transcription rate of operon because of DNA bending of CAP-cAMP · bending might allow RNAp to bind tightly to promoter * possibilities for lac mRNA Synthesis of arabinose * regulation operon It is ↳ an operon that has both positive and negative regulation ↳ consists of 3 structural genes · ara B , araA , araD  #how are the 3 structural genes transcribed by ↳ transcribed as polysistronic mRNA ↳ encode the 3 arabinose metabolizing enzymes ↳ araC encodes control protein Arac ↳ arabinose is absent · Ara C protein acts as a negative regulator , dimer and causes the to DNA loop · looping brings the 1 , and O2 sites closer to each other · one trac monomer binds to 1 , and second trac monomer binds to 02 what # does the binding of trac prevent ? ↳ RNAP from binding to Abad promoter ↳ arabinose is present · acts as an inducer and binds to trac and changes its conformation ↳ arabinose - Ara Cdimer Complex binds to 1 , and 12 Not 02 # Why does it not bind to O2 ? ↳ because it of the loop which allows causes the opening RNAP to bind to Prad ↳ glucose levels are low · CAMP-CAP complex binds to Pc and active transcription starts * negative autoregulation of arac transcription ↳ level of ara) expression is controled by the amount of ara C protein # what does high levels of ara ( do? ↳ causes proteins to bind to 0, and inhibit transcription the PC promoter 23the more araprotein in the cell the more ava (mRNA is made autoregulation * mechanism 2 : activation polymerase ↳ works for 854 promoters · it's RNAP makes a Stable complex with DNA but needs to be activated to form an open complex G RNAP 654 complex need ATP hydrolysis to form # what birds to ennancor and where ? ↳ activator protein with ATPase activity , 160bp upstream - 24 ↳ DNA gets looped and activator interacts with RNAP-854 which results open bubble formation upon ATP in hydrolysis