assignment

Prokaryotic gene regulation study sheet : Lac Operon an Inducible operon

1: sketch the elements of the lac operon:

2. Complete the table:

	environment
	Glucose	Lactose	Lac I status Bound to allolactose? Bound to operator?	cAMP status High or low? bound to CAP or not?	Transcription of ZYA ? yes or no?
1	-	-
2	+	-
3	+	+
4	-	+
5	- + + -	- - + +	Mutated LacI gene (a)*
6	- + + -	- - + +	Mutated operator
7	- + + -	- - + +	Mutated LacI gene (b)**

*Mutated LacI gene (a): mutated sequence so that I protein I is made, but cannot bind to DNA

**Mutated LacI gene (b): mutated sequence so that I protein I is made, but cannot bind to allolactose

3. Now, what if there was a single base deletion, causing a frameshift and premature stop in the LacZ gene? Would LacA protein (permease) be made?

4. And so, what if there was a single base deletion causing a frameshift and premature stop in the LacA gene? Would LacZ protein (β galactosidase) be made?

Tryptophan operon – a repressible operon

1. Sketch the elements of the trp operon, including the leader sequence.

2. Complete the table

	Tryptophan	Repressor status Bound to trp or unbound?	Operator status Bound or open?	Attenuator status (which regions 1-2, 2-3, 3-4 are basepaired, if any? Is it a stop hairpin?)	Transcription of trp genes? Yes or no?
1	low
2	high

3. What would happen if there is a mutation in the gene for the trp repressor protein such that it will bind to the operator sequence even without the corepressor?

4. What would happen if there is a mutation in operator sequence, such that the trp repressor cannot bind there?

5. What would happen if the leader sequence was mutated in region 3, such that the it was missing?