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he T l a c Oper on - a n i nduci bl e system La ctose ----------------> Gl ucose + Ga l a ctose -ga l a ctosi da se Di auxi c Gr owth Cur ve 5 4 3 2 1 0 0 5 10 lo (Nu ber o g m f B act eria) Ti me i n hour s 5 4 3 What was happeni ng? 2 1 0 0 5 10 log (N umber of Bact er ia) The cells use glucose fir st . When t hey r un out of glucose, t hey use lact ose. Bet a galact osidase is not expr essed unless: 1) Ther e is no glucose. 2) Ther e is lact ose. T wo ca tegor i es of tr a nscr i pti on r egul a ti on N ega ti ve contr ol : r epr essor pr otei n pr esent whi ch pr events tr anscr i pti on, i nducer (usual l y a smal l mol ecul e) i s needed to al l ow i ni ti ati on of tr anscr i pti on. Posi ti ve contr ol : acti vator pr otei n i nduces tr anscr i pti on. No r epr essor must be over r i dden. Repr essor Pr otei ns Repr essor pr otei ns bi nd to a n oper at or si te wi thi n the pr omoter . Bi ndi ng of a r epr essor pr events bi ndi ng of RN A pol ymer a se T he r epr essor i s a n a l l oster i c pr otei n tha t ca n be a cti va ted by bi ndi ng to a sma l l mol ecul e Acti va tor Pr otei ns Acti va tor pr otei ns bi nd to D N A sequences a nd then i nter a ct wi th RN A pol ymer a se to enha nce i ts bi ndi ng. Acti va tor pr otei ns ca n be a l l oster i c a nd bi nd to sma l l mol ecul es befor e they ca n bi nd to D N A. The oper on: A gr oup of genes whose expr essi on i s coor di nated by an oper ator (F. J acob et al .) 1960. The oper on: The pr omot er : A geneti c el ement necessar y for the expr essi on of an oper on (F. J acob et al .) 1964. ctose La meta bol i sm in E. col i . Enzymes necessa r y for l a ctose meta bol i sm: -galact osidase (cleaves lact ose int o glucose and galact ose) lact ose per mease (t r anspor t s lact ose int o t he cell) t r ansacet ylase (funct ion unknown) The l a c oper on l acZ ( -gal actosi dase) l acY (l actose per mease) l acA (tr ansacetyl ase) Walt er Gilber t I n the mi ddl e si xti es, Benno M l l er H i l l a nd I i sol a ted the l a ctose r epr essor : the fi r st exa mpl e of a geneti c contr ol el ement. A r epr essor i s a pr otei n pr oduct ma de by one gene i n the ba cter i um i n or der to contr ol a second gene by tur ni ng i t off when i ts pr oduct i s not Walt er Gilber t t oday T he r ol e of the exon i n evol uti on H ow ha s the exon str uctur e of euka r yoti c genes a ffected evol uti on? D o exons pr eda te the euka r yote-pr oka r yote spl i t? We conclude t hat int r ons ar e cor r elat ed wit h compact feat ur es of pr ot eins 15-, 22-, or 30amino acid r esidues long, as was pr edict ed by "The Exon Theor y of Genes." Gener al catabol yte r epr essi on. Glucose levels ar e cor r elat ed t o t he concent r at ion of cAM P via t he enzyme t hat synt hesizes cAM P, adenylyl cyclase. H igh glucose levels adenylyl cyclase low cAM P levels adenylyl cyclase high cAM P levels L ow glucose levels Revi ew How does E. coli prevent expression of the lactose enzymes in the absence of lactose? How does E. coli prevent expression of the lactose enzymes in the presence of glucose? Regul a ti on of tr yptopha n synthesi s Acti va tor Pr otei ns

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