Gene Regulation and Cellular Responses Quiz

Repressor proteins play a key role in gene regulation by binding to the operator of an operon, thereby preventing RNA polymerase from transcribing the genes. This effectively switches the operon off. Repressor proteins can be regulated by environmental factors, such as the presence of specific molecules (inducers or corepressors), which can bind to the repressor and alter its ability to bind to the operator, thus switching the operon on or off in response to changing conditions.

The trp operon is a repressible operon involved in the production of tryptophan. When tryptophan levels are low, the repressor is inactive, allowing gene expression to occur. However, when tryptophan is present, it binds to the repressor, activating it, and causing the repressor to bind to the operator, thereby turning the operon off and decreasing gene expression.

Inducible operons are usually turned off but can be turned on in the presence of an inducer molecule. The lac operon is an example of an inducible operon, and its gene expression is usually off, but can be turned on when lactose is present. Repressible operons are usually on but can be turned off in the presence of a corepressor molecule. The trp operon is an example of a repressible operon, and its gene expression occurs by default, but can be turned off when tryptophan is present.

<p>The CAP-cAMP complex, activated in response to low glucose levels, acts as a positive regulator in the lac operon. When glucose is scarce, the complex binds to the promoter of the lac operon, increasing the affinity of RNA polymerase for the promoter and stimulating gene expression.</p> Signup and view all the answers

<p>The trp and lac operons involve negative gene regulation through the activity of repressor proteins, which can switch the operons off in response to specific molecules (tryptophan for trp operon, lactose for lac operon). Additionally, the lac operon also involves positive gene regulation through the CAP-cAMP complex, which enhances gene expression when glucose is scarce.</p> Signup and view all the answers

<p>It prevents gene transcription by binding to the operator and blocking RNA polymerase.</p> Signup and view all the answers

<p>Tryptophan binding to the repressor protein</p> Signup and view all the answers

<p>It increases the affinity of RNA polymerase by binding to the promoter.</p> Signup and view all the answers

<p>It is usually off but can be turned on when an inducer binds to the repressor.</p> Signup and view all the answers

<p>The active form of the repressor switches off the operon.</p> Signup and view all the answers