Quiz 1: Regulation Of Transcription In Prokaryote

Repression refers to the control of gene expression by preventing a gene from being expressed. It involves the binding of repressor proteins to the DNA, which inhibits the transcription of the gene. This prevents the production of mRNA and subsequently the translation of the mRNA into a protein. Repression is an important mechanism in regulating gene expression and allows cells to respond to different environmental conditions or developmental stages by selectively repressing certain genes.

A promoter is a DNA sequence that is located upstream from a gene and serves as the binding site for RNA polymerase. RNA polymerase is an enzyme responsible for initiating the transcription process, where a complementary RNA molecule is synthesized from the DNA template. The promoter region plays a crucial role in gene regulation by determining when and how often a gene is transcribed. By binding to the promoter, RNA polymerase helps to initiate the transcription process and allows for the expression of the gene.

Polycistronic refers to an mRNA molecule that contains multiple coding regions, or open reading frames (ORFs), which can be translated into two or more proteins. In polycistronic mRNA, the coding regions are typically separated by short non-coding regions called intercistronic regions. This arrangement allows for the coordinated expression of multiple genes in prokaryotes, where several genes involved in a common function are transcribed together as a single mRNA molecule. This enables efficient regulation and simultaneous production of multiple proteins that work together in a specific pathway or process.

The correct answer is lacZ because it is the gene that encodes for beta-galactosidase. Beta-galactosidase is an enzyme that is involved in the breakdown of lactose into glucose and galactose. The lacZ gene is part of the lac operon in E. coli and is responsible for the production of beta-galactosidase, which allows the bacteria to utilize lactose as a carbon source. The other options (lacY, lacA, lacZY, lacZYA) are not the specific gene for beta-galactosidase.

An operon is a group of linked genes whose expression is coordinately regulated. In an operon, multiple genes are transcribed together as a single mRNA molecule, allowing for efficient regulation of gene expression. The operon is controlled by a promoter, which initiates transcription, and an operator, which acts as a switch to turn gene expression on or off. The regulator and repressor proteins bind to the operator and regulate the expression of the operon by blocking or allowing transcription. Therefore, the correct answer is operon.

The operator is the region of an operon that is located close to the promoter and is responsible for binding to a repressor protein. This binding prevents the RNA polymerase from transcribing the genes in the operon, effectively turning off gene expression. The operator acts as a regulatory element that controls the expression of the operon by determining whether the genes are transcribed or not.

The trpE gene contains a 5’ untranslated region that plays an important role in the regulatory mechanism called attenuation. Attenuation is a process in gene regulation where the transcription of the gene is prematurely terminated. In the case of the trpE gene, the 5’ untranslated region can form specific secondary structures that can either allow or prevent the formation of a transcription termination hairpin. This mechanism controls the expression of the trpE gene based on the availability of tryptophan in the cell. When tryptophan levels are low, the ribosome stalls at the trp codons, allowing the formation of the transcription termination hairpin and resulting in attenuation of gene expression.

The correct answer is 3 and 4. The attenuator hairpin is formed by the base pairing of sequences 3 and 4.

Tryptophan, as the end-product of the enzymes encoded by the trp operon, acts as a co-repressor. This means that when tryptophan levels are high, it binds to the repressor protein and together they bind to the operator region of the operon. This binding prevents RNA polymerase from transcribing the genes in the operon, effectively shutting down the production of tryptophan. Therefore, tryptophan acts as a co-repressor, working in conjunction with the repressor to regulate the expression of the trp operon.

Allolactose is the correct answer because it is a sugar molecule that acts as an inducer for the lac operon. The lac operon is a group of genes involved in lactose metabolism in bacteria. When lactose is present in the environment, it is converted into allolactose, which binds to the lac repressor protein and prevents it from binding to the lac operator. This allows RNA polymerase to bind to the promoter and transcribe the genes involved in lactose metabolism. Therefore, allolactose is the true inducer of the lac operon.