Final answer:
Yeast gal genes are regulated by b) repressor that is inactivated by galactose, while E. coli lactose metabolism genes are part of an inducible operon system regulated by both an inducer and a repressor affected by lactose and glucose levels respectively. The lac operon requires both low glucose and presence of lactose for transcription, reflecting a coordinated response to environmental nutrient conditions.
Step-by-step explanation:
To compare and contrast the transcriptional regulation of gal genes in yeast with that of the lac genes in bacteria, we can look at the use of inducers, repressors, promoters, and operators.
In yeast, the transcriptional regulation involves the use of a repressor that can be inactivated by the presence of galactose, whereas in E. coli bacteria, the lac operon system utilizes both a repressor and an inducer. The gal genes are not organized into an operon as they are in bacterial cells.
The lac operon in E. coli includes the lacZ, lacY, and lacA genes, encoding ß-galactosidase, lactose permease, and a transacetylase, respectively. It is regulated by a repressor protein encoded by the regulatory I gene, which binds to the operator sequence to prevent transcription. In the presence of lactose, an inducer molecule binds to the repressor, causing a conformational change that prevents the repressor from binding to the operator, allowing transcription to proceed.
Additionally, when glucose levels are low, cAMP levels increase, leading to the activation of CAP which binds to the promoter to facilitate RNA polymerase binding and initiate transcription. Both the low glucose and presence of lactose conditions must be met for transcription of the lac operon to be induced.
Therefore, the key difference in the regulation of gal genes and lac genes lies in the coordination and regulation mechanisms, with the lac operon being influenced by both glucose and lactose levels for transcription to occur, whereas yeast gal genes are directly regulated by a single sugar, galactose.