Question

1. Suppose you become proficient with a technique that allows you to move DNA sequences within a prokaryotic genome.

1. You are given a wild-type cell that is placed on media with high levels of lactose and no glucose. If you move the promoter for the lac operon to the region between the lacZ gene and the lacY gene, what protein(s) associated with the lac operon will and will NOT ultimately be produced? Explain your logic. You may assume that there are no other mutations in the cell other than the change you introduced.
2. You start with a new wild-type cell, this time placed in media with no lactose and high levels of glucose. This time you move the operator to the far end of the operon, past the lacA gene. What would most likely occur in this scenario, again assuming that there are no other mutations other than this one change you have introduced? Explain your logic.
3. You really like using this technique and start with another wild-type cell. You again grow the cell in media with no lactose and high levels of glucose. You move the lacI gene, along with its promoter, to a position at some several thousand base pairs downstream from the lacA gene. What would most likely occur, again assuming that the cell is otherwise wild-type, and the previous changes made do not carry over? Explain your logic.

Answer 1

a)There will be formation of only Permease and transacetylase. No formation of beta galactosidase because promoter is present b/w z and a lac gene.

Lactose will make repressor protein inactive and operator will remain free and allow RNA polymerase to bind with promoter. So there will only transcription and translation of lac y and lac a gene.

b)There will no formation of any enzyme because for action of lac operon presence of lactose is important. If lactose is not present in medium then Repressor protein produced by i gene will bind with operator.If this happen then RNA polymerase will not be able to bind with promoter. So no transcription and no translation.

c).Same thing will happen in this case too as in above case because again there is no lactose in medium.