Regulation of lac and ara Operons Quiz

<p>It represses the operon by binding the operator region</p> Signup and view all the answers

<p>It cannot bind the operator, allowing transcription from the trp operon to be initiated</p> Signup and view all the answers

<p>It binds to tryptophan, serving as an effector and blocking transcription from the trp operon</p> Signup and view all the answers

<p>They can base-pair to form a stem-and-loop structure, acting as a transcriptional terminator</p> Signup and view all the answers

<p>Sequences 3 &amp; 4 form a hairpin, RNA Pol stalls, and transcription is terminated</p> Signup and view all the answers

<p>The amount of free tryptophan available for protein synthesis</p> Signup and view all the answers

<p>Up to ~70 fold by the repressor system alone</p> Signup and view all the answers

<p>It can repress the expression of the trp genes up to ~700 fold</p> Signup and view all the answers

<p>It has 14 amino acids, two of which are Trp</p> Signup and view all the answers

<p>Mediates lactose entry into the cell</p> Signup and view all the answers

<p>Acts like allolactose, inducing transcription</p> Signup and view all the answers

<p>Recognizes X-Gal as a substrate, aiding in blue-white selection</p> Signup and view all the answers

<p>Blocks expression of lac genes when glucose is available</p> Signup and view all the answers

<p>Through cAMP and CRP-mediated regulation</p> Signup and view all the answers

<p>By AraC protein, arabinose, and cAMP/CRP</p> Signup and view all the answers

<p>AraC binding arabinose</p> Signup and view all the answers

<p>Modifies toxic galactosides imported with lactose</p> Signup and view all the answers

<p>lacY protein</p> Signup and view all the answers

<p>Acts as a positive regulator, influencing gene expression</p> Signup and view all the answers

<p>AraC protein</p> Signup and view all the answers

<p>LacZ recognizing X-Gal as a substrate</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Trp repressor = Forms a complex with tryptophan to bind the operator and block transcription Attenuation sequence 3 and 4 = Can base-pair to form a stem-and-loop structure which acts as a transcriptional terminator Leader peptide = Translated from sequence 1 and contains two Trp codons tRNATrp and ribosomes = Affect the formation of a hairpin structure in the attenuation process</p> Signup and view all the answers

<p>High [tryptophan] = Results in the formation of a Trp-repressor complex that binds the operator and terminates transcription Low Trp [tRNA] and ribosome stalling = Allows sequences 2 and 3 to associate and form a hairpin, preventing transcriptional termination High [tRNATrp] = Leads to rapid translation through Trp codons and formation of a transcriptional terminator Low [tryptophan] = Causes ribosome stalling on Trp codons of sequence 1 and allows the formation of a hairpin structure</p> Signup and view all the answers

<p>Repressor system alone = Can repress the trp operon expression by up to ~70 fold in the absence of tryptophan Repressor-attenuation system combined = Can achieve up to ~700 fold repression of the trp operon expression in the absence of tryptophan Free tryptophan availability = Determines the level at which the trp operon is transcribed Attenuation process = Involves the formation of a stem-and-loop structure by sequences 3 and 4, acting as a transcriptional terminator</p> Signup and view all the answers

<p>The trp operon is regulated by a repressor system and attenuation. In the absence of tryptophan, the Trp repressor cannot bind the operator, leading to initiation of transcription and tryptophan production. However, when tryptophan is abundant, it serves as an effector for the Trp repressor, leading to the formation of a Trp-repressor complex that blocks transcription. Additionally, attenuation occurs through the regulation of transcription that is in progress, where the level of free tryptophan determines the transcription level of the trp operon.</p> Signup and view all the answers

<p>Attenuation of the trp operon occurs through the regulation of transcription that is in progress. The trp mRNA includes a 5’ leader sequence containing four regulatory regions. When tryptophan levels are high, tRNATrp is also high, and ribosomes translate quickly through Trp codons, leading to the formation of a hairpin and termination of transcription. On the other hand, in the absence of tryptophan, tRNA levels are low, and ribosomes stall on Trp codons, allowing the formation of a different hairpin that does not terminate transcription. Therefore, the level of free tryptophan determines the expression level of the trp operon.</p> Signup and view all the answers

<p>In the absence of tryptophan, the expression of the trp genes can be repressed by the repressor system alone up to ~70 fold, and up to ~700 fold by the repressor-attenuation system combined. The Trp repressor system prevents the binding of the Trp repressor to the operator, allowing transcription initiation and tryptophan production. However, the combined repressor-attenuation system further enhances the repression of trp gene expression by regulating transcription in progress, based on the level of free tryptophan available for protein synthesis.</p> Signup and view all the answers