The activator (V protein) that is present in the bacterial cell is normally phosphorylated, but only binds to the A site in the operon when it is not phosphorylated. What operon-independent mechanism can regulate the binding of (and also ultimately regulates the removal of) protein V to the A site? Describe this binding/removal mechanism in detail – useappropriateterminologythatwasdiscussedinlecture. Aspartofyouransweraboutthisactivatorproteinbindingto (and then detaching from) the A site of the operon, be sure to address what are the results of this type of control in terms of function of the operon.

What is lac operon? Draw and/or identify the status of the lac operon in a given set of environmental conditions and/or cell mutations.

The figure at the beginning of this chapter showsthe binding of both a Lac repressor tetramer and aCRP-cAMP complex to the regulatory region of thelac operon.a. What is the key feature of a regulatory protein suchas the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposedto control?b. On the figure, show the positions of the followingcomponents: (i) A Lac repressor monomer; (ii) a Lacrepressor dimer; (iii) all four DNA binding domains ofthe Lac repressor tetramer; (iv) a single helix-turnhelix motif; (v) the o1 part and either the o2 or o3 partsof the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) themultimerization domains of the four Lac repressormonomers; (vii) an inducer-interacting domain; (viii)the CRP-cAMP complex; and (ix) a DNA loop.c. What is the physical basis for the formation of theDNA loop shown in the figure?d. On the figure, show the position of two axes ofsymmetry in the sequence…

What properties demonstrate that the lac repressor is a protein?Describe the evidence that it indeed serves as a repressor withinthe operon system.

Bob determines that Red/pink protein is synthesized at much higher amounts than the Brown protein; Bob thinks that this is how the burger always is perfectly medium-rare (pink/red in the interior of the patty, with a small amount of brown at the burger’s surface). Bob also knows that R and B both are transcribed from the single operon. Briefly describe the biological mechanism allowing for accumulation of more R than B protein.

1) A. What is the difference between a repressible vs, an inducible operon?   B. Using diagrams and words, describe how the Lac Operon is regulated by different levels of lactose and glucose. Be sure to show what’s happening at the molecular level, including the roles of lactose, glucose the repressor protein, cAMP and CAP.

8&9

A number of mutations affect the expression of the lac operon in E. coli. The genotypes of several E. coli strains are shown below. ("+" indicates a wild-type gene with normal function and "-" indicates a loss-of-function allele.) Please predict which of the following strains would have the lowest beta-galactosidase enzyme activity, when grown in the lactose medium. OF POZY Ort Ptot Z¹ Yt Ort p²o+z¹Y+ Orpt ot zty