Question

1.    Under which conditions would the lac operon produce the greatest amount of ?-galactosidase? The least? Explain your reasoning.

                                    Lactose present     Glucose Present

            Condition 1               Yes                             No

            Condition 2               No                               Yes

            Condition 3               Yes                             Yes

            Condition 4               No                               No

Answer 1

Please find the answers below:

Lac operon is an inducible operon which encodes for gene beta galactosidase for degradation of lactose as a preferred substrate rather than glucose. Thus, presence of glucose prevents expression whereas presence of lactose up-regulates expression. Thus, the answers can be found as below:

Answer 1: Strong expression (since the inducer or lactose is present and repressor or glucose is absent, strong expression will take place)

Answer 2: No expression (lac operon does not operate in presence of glucose and absence of lactose as glucose will not induce transcription in genes)

Answer 3: Mild expression (although lactose is present, the presence of glucose will partially mask the operator and thus presvent complete expression of the cistron)

Answer 4: No expression (Since lactose is altogether absent, no expression of beta galactosidase will be required by the cells)