Question

Bacterial cells regulate gene expression at both transcription and translation levels. Transcription is controlled by transcription factors or DNA binding proteins that bind promoters (regulatory sequences of genes) and prevent or promote RNA Polymerase binding. Positive control of transcription involves both disabling a repressor and allowing an activator to bind the promoter. Similarly, negative control results in detachment of the activator and binding of the repressor to turn off transcription. Inducible genes encode enzymes involved in catabolic pathways. These genes are turned off by binding of repressors to the operator site (downstream to or overlapping the promoter sequence). To turn them on, an inducer inactivates the repressor causing it to fall off. The promoter is then free to bind an activator at the activator binding site, which further promotes RNA polymerase binding. Repressible genes generally encode enzymes that are part of the anabolic pathways. These genes are generally on until turned off. The aporepressor must be activated by product of the anabolic pathway by a negative feedback mechanism. Thus, the product acts as a corepressor to turn off transcription. The genes are turned back on when co-repressor diffuses away causing the repressor to fall off.

Questions: Bacterial cells must monitor their environment to make appropriate regulatory decisions. Catabolic enzymes are involved in breaking down a nutrient whereas anabolic enzymes are involved in synthesizing an essential nutrient. Let’s assume that bacteria are inoculated into a medium containing both maltose sugar and proline amino acid. Determine whether the MAL and PRO operons will be ON or OFF?

Answer 1

Answer:

• Maltose sugar is made up of two molecules of glucose and bacterial cells metabolize maltose sugar for energy production and hence MAL operon is a catabolic operon because as a result of this operon the maltose is breaking down and used up by the bacterial cells for energy production.
• So if the media contains the maltose sugar than the MAL operon will be turned on as the maltose sugar will bind to the repressor protein and the repressor protein inactivates by means of conformation change.
• Now this repressor protein is not able to bind to the operator sequence and that's why transcription and translation of MAL operon genes takes place and cell uses maltose for energy production.
• Now in case of PRO operon, the baceterial cells make proline amino acid from glutamate and this pathway utilizes three enzymes coded by this PRO operon.
• So this means that the PRO operon is anabolic operon because in this operon synthesis of proline takes place.
• So if the media is already providing proline amino acid than there is no need for the translation of these three enzymes and that's why the proline amino acid binds with the aporepressor and activates it.
• The activated repressor binds to the operator region in the operon and becasue of this binding the RNA polymerase will be halted so that no transcription takes place and in this way bacterial cell will avoid synthesizing proline amino acid when there is an abundance of this amino acid in the growth media.

So when bacterial cells are inoculated into a medium containing both maltose sugar and proline amino acid then MAL operon will be turned On as it is a catabolic operon and PRO operon will be turned Off as it is an anabolic operon.

Please Rate My Answer.......................Thank..............u....