When is the lactose repressor bound to the lac operon?

When is the lactose repressor bound to the lac operon?

The lac repressor and catabolite activator protein are two regulators that switch the operon "on" and "off" in response to lactose and glucose levels (CAP). Lactose is sensed by the lac repressor. It generally inhibits operon transcription, but stops functioning as a repressor when lactose is present. Glucose can bind to the CAP protein and prevent it from activating transcription. The presence of both lactose and glucose results in both proteins returning to their inactive states and allowing transcription to resume.

Lactose represses transcription of the operon by binding to the lac repressor. This prevents RNA polymerase from recognizing the promoter region of the operon and causing transcription to begin. Glucose binds to the catabolite activator protein (CAP) and prevents it from activating transcription. With both sugars present, the lac repressor and catabolite activator protein return to their inactive states and allow transcription to resume.

Glucose promotes its own synthesis by binding to the catabolite activator protein (CAP). This prevents it from activating transcription. With both sugars present, the catabolite activator protein returns to its inactive state and allows transcription to resume.

Thus, the presence of glucose prevents its own synthesis. This forms part of the complex regulation involved in maintaining the appropriate levels of nutrients in cells. When nutrient levels are low, genes associated with using up these nutrients are turned on by proteins such as catabolite activator protein.

What can be concluded regarding the Lac I gene?

It is only expressed when lactose is present and glucose is not. Lactose permease allows glucose into cells while at the same time exporting lactose out of cells.

LacI is responsible for binding to specific locations (lac operators) on the DNA. This binding prevents RNA polymerases from accessing the DNA and therefore prevents transcription of the genes inside the operon. Removal of LacI allows transcription to begin again once it has dropped off the DNA.

The presence of CAP increases the rate at which lactose enters bacteria through lactose permease and out through glucose permease. Bacteria cannot metabolize lactose so it is excreted via urine or feces where it is broken down into glucose and galactose. Glucose then becomes available for other organisms to use as energy. Galactose is recycled back into lactose by galactosidases found inside bacteria or fungi.

Bacteria do not have enzymes to break down glucose so it is used as an energy source instead. However, most bacteria don't need this extra energy so they leave it unused.

How do the E. coli cells in our intestines regulate the metabolism of lactose?

Lactose metabolism genes are found in E. coli. When no lactose is present, the repressor binds to the promoter region of the operon and prevents expression of the genes inside. When lactose is present, the repressor leaves the operon without binding to any DNA sequence so the genes can be expressed.

The catabolite activator protein acts next. It searches for unbound repressors in the cell and removes them so the genes can be expressed. Without this protein, most E. coli genes would be on all the time because there would be no way for the cell to turn them off.

Lactose is used as a source of energy by many bacteria including E. coli. However, most humans cannot digest lactose which allows E. coli to use it as a source of fuel instead of sugar. Humans also don't have any enzymes to break down lactose so it passes through us undigested. Our bodies can use the nutrients inside dairy products for other purposes rather than absorbing them. For example, we can produce antibodies against proteins contained in milk so they can be used as vaccines later on.

About Article Author

Walter Hall

Walter Hall is an avid reader and seeker of knowledge. He enjoys learning about new things, such as planets, minerals, and metals. Walter also likes reading about other topics such as education reform and the Common Core State Standards.

Disclaimer

BartlesVilleSchools.org is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

Related posts