Final answer:
A mutation in the consensus sequence of the lac promoter can lead to blocked transcription if it inhibits RNA polymerase binding or constitutive transcription if it prevents repressor binding. The mutation's impact depends on its nature and which regulatory mechanism it affects.
Step-by-step explanation:
The lac operon is an essential system in bacteria like E. coli for metabolizing lactose when glucose is not available. A mutation in the consensus sequence of the lac promoter could lead to two possible outcomes. If the mutation prevents RNA polymerase from binding, it will block transcription. On the other hand, if the mutation prevents the repressor from binding the operator, transcription could become constitutive, where the operon is always active.
Mutations in the lac operon's structural genes (lacZ, lacY, and lacA) will typically result in loss of function for the corresponding enzyme that the gene codes for. This could result in the inability of the cell to metabolize lactose because the necessary enzymes are either not produced or are nonfunctional. Mutations in the operator sequence that prevent repressor protein binding will lead to constant transcription of the operon, even in the absence of lactose, since there is no repression. Therefore, depending on the nature of the mutation in the promoter, the effect on gene transcription will vary significantly.