Question

Record what you expect the expression pattern of the structural gene (s) to be, given the absence/presence of the environmental signal, and the genotype of the regulatory gene (r) or the operator (o). write "on" when you expect the structural gene to be expressed, and "off" when you expect it to be repressed. r o s

Answer 1

The expression of structural genes is 'on' or 'off' based on the binding of repressors or activators to the operator in the regulatory region, which is influenced by surrounding environmental signals and the genotype of regulatory elements. For example, the lac operon in E. coli is 'off' when glucose is high and 'on' when lactose is present as the sole carbon source, due to the action of inducers on the regulatory proteins.

Step-by-step explanation:

The expression pattern of structural genes (s) depends on the presence of an environmental signal and the genotype of the regulatory gene (r) or the operator (o). When an environmental signal is present and it necessitates the expression of the structural genes, and if the regulatory region (including the promoter and operator) is free from a repressor, the genes will be 'on', leading to transcription. If a repressor is bound, or the necessary signal or activator is absent, the structural genes will be 'off' and not transcribed. In the case of regulatory genes, if they produce a functional repressor that binds to the operator in the absence of an inducer, they will prevent the transcription of the structural genes. In contrast, if an inducer is present that inactivates the repressor, or if the genotype of the regulatory gene produces a non-functional repressor, the structural genes will be expressed.

The lac operon in E. coli, for example, is typically 'off' when glucose is present because the repressor is active and the operon is not needed for lactose metabolism. Conversely, when lactose is available and glucose is low or absent, an inducer binds to the repressor making it inactive. This allows the operon to be 'on' and the proteins necessary for lactose metabolism to be produced. For the trp operon, which is responsible for the synthesis of tryptophan, it is 'on' by default because the cell typically needs to produce tryptophan, but it will be turned 'off' if tryptophan levels are sufficient and acts as a corepressor to activate the repressor protein, preventing unnecessary production.