Genetics And Gene Mutation Trivia Quiz

A repressor is a type of regulator protein that binds to a region of DNA in the promoter of a gene called the operator and prevents transcription from taking place. The operator is a specific DNA sequence that acts as a binding site for the repressor protein. When the repressor binds to the operator, it blocks the RNA polymerase from binding to the promoter and initiating transcription. This mechanism allows the repressor to regulate gene expression by controlling whether or not the gene is transcribed.

A promoter that affects only genes that are on the same piece of DNA is referred to as "cis-acting." The term "cis" in this context indicates that the regulatory element is located on the same DNA molecule as the genes it influences. This is in contrast to "trans-acting" elements, which can regulate genes located on different DNA molecules. The concept of cis-acting elements is important in understanding gene regulation and the coordination of gene expression within a specific genomic region.

An inducible gene is a gene that is transcribed, or activated, when a specific substance is present. This means that the presence of this substance triggers the transcription of the gene, leading to the production of the corresponding protein. Therefore, the statement "An inducible gene is transcribed when a specific substance is present" is true.

When a structural gene is under negative inducible control, it means that the gene is normally repressed by a repressor protein. In this case, if a mutation occurs that eliminates the repressor protein, there will be no inhibition of the gene expression. As a result, the structural gene will be expressed continuously or constitutively, regardless of the presence or absence of an inducer. Therefore, the statement "a mutation that eliminates the repressor protein will cause the structural gene to be constitutively expressed" is true.

A repressible gene is controlled by a regulatory protein that inhibits transcription. This means that the gene is normally active and producing its corresponding protein, but can be turned off or repressed by the presence of a regulatory protein. This regulatory protein binds to the gene's promoter region and prevents the RNA polymerase enzyme from binding and initiating transcription. Therefore, the statement "A repressible gene is controlled by a regulatory protein that inhibits transcription" is true.

In positive repressible control, the normal state is indeed transcription of a gene, which is stimulated by a transcriptional activator. This means that the gene is normally being transcribed unless it is repressed by a specific factor. Therefore, the statement "the normal state is transcription of a gene, stimulated by a transcriptional activator" is true.

Regulatory genes are responsible for controlling the expression of other genes. They produce products that can be either RNA or proteins. This means that the statement "Regulatory genes are genes whose products are either RNA or proteins" is true.

Attenuation is a type of transcriptional control that regulates the continuation of transcription. It occurs in certain bacterial operons where the rate of transcription can be affected by the presence or absence of specific molecules. Attenuation involves the formation of alternative RNA secondary structures during transcription, which can either allow or prevent the continuation of transcription. This mechanism allows the cell to quickly respond to changes in the availability of certain molecules and adjust gene expression accordingly.

The inducer molecule binds to the repressor protein and causes a change in its structure, which prevents the repressor from binding to DNA. This type of regulation, where the binding of a molecule at one site affects the activity at another site, is known as allosteric regulation. Therefore, the correct answer is allosteric.

In the absence of allolactose, the lac operon is not constitutively transcribed. The lac operon is a group of genes involved in the metabolism of lactose in bacteria. It is regulated by a repressor protein that binds to the operator region and prevents transcription of the genes. In the absence of allolactose, the repressor protein remains bound to the operator, blocking transcription. When allolactose is present, it binds to the repressor, causing a conformational change that releases the repressor from the operator, allowing transcription to occur. Therefore, the absence of allolactose does not lead to constitutive transcription of the lac operon.

The correct answer is that the repressor binding site overlaps the promoter site of the operon, allowing it to physically block the binding of RNA polymerase. This means that when the repressor binds to the DNA, it prevents RNA polymerase from binding to the promoter region and initiating transcription. As a result, the expression of the operon is negatively regulated, as transcription cannot occur.

cAMP, or cyclic adenosine monophosphate, plays a crucial role in the regulation of the lac operon. In the presence of glucose, cAMP levels are low, and the lac operon remains inactive. However, when glucose levels are low, cAMP levels increase, and cAMP binds to the activator protein called CAP (catabolite activator protein). The cAMP-CAP complex then binds to the promoter region of the lac operon, enhancing the binding of RNA polymerase and promoting transcription of the lac genes. Therefore, cAMP activates the activator protein CAP, which is required for the expression of the lac operon.

The correct answer is I, Z, Y, A. This is because the lac I gene and lac operon structural genes Z, Y, and A are responsible for encoding proteins. The lac I gene encodes the lac repressor protein, which regulates the expression of the lac operon. The lac operon structural genes Z, Y, and A encode the proteins necessary for the metabolism of lactose. The lac promoter (P) and operator (O) are regulatory regions of the DNA and do not directly encode proteins.

Allolactose acts as an inducer in the regulation of the lac operon. It binds to the repressor protein, causing a conformational change that prevents it from binding to the operator region of the operon. This allows RNA polymerase to bind to the promoter region and transcribe the genes involved in lactose metabolism. Therefore, allolactose helps to activate the lac operon by relieving the repression imposed by the repressor protein.

When a structural gene is under positive inducible control, it means that the expression of the gene is normally turned off and requires the presence of an activator protein to be turned on. If a mutation occurs that eliminates the activator protein, the gene will not be able to be turned on and therefore will not be constitutively expressed. Therefore, the correct answer is false.

In the absence of tryptophan, the genes of the trp operon are actually expressed. The trp operon is a set of genes responsible for the synthesis of tryptophan in bacteria. When tryptophan is present in the environment, it binds to a repressor protein, which then binds to the operator region of the operon, preventing the expression of the genes. However, in the absence of tryptophan, the repressor protein is unable to bind to the operator region, allowing the genes to be expressed and leading to the synthesis of tryptophan. Therefore, the statement that the genes of the trp operon are not expressed in the absence of tryptophan is false.

Acetylation is the modification that neutralizes the charges on histones that promote ionic interaction with DNA. Acetylation involves the addition of an acetyl group to the histone proteins, which reduces the positive charge on the histones. This reduction in positive charge weakens the interaction between histones and DNA, allowing for a more relaxed and open chromatin structure. This modification is important for gene expression regulation, as it allows for easier access of transcription factors and other proteins to the DNA.

The lac operon in E. coli is controlled by CAP (catabolite activator protein). CAP acts as a positive regulator, meaning it enhances the transcription of the lac operon genes in the presence of an inducer molecule, such as lactose. This is known as positive inducible control because the presence of the inducer molecule induces the expression of the lac operon genes. Therefore, the correct answer is positive inducible.

This statement is false because not all DNA sequences are transcribed into mRNA molecules. Only certain sections of DNA, known as genes, are transcribed into mRNA. Genes contain the instructions for building proteins, and these instructions are transcribed into mRNA through a process called transcription. So, while genes are DNA sequences that are transcribed into mRNA, not all DNA sequences are genes.

An operon is controlled by a repressor that binds to DNA near the operon. In the case of negative repressible operons, the repressor is normally bound to the operator region, preventing transcription of the operon. However, when a small molecule binds to the repressor, it undergoes a conformational change and is released from the operator, allowing transcription to occur. Therefore, the operon is repressed in the absence of the small molecule, and its expression is negatively regulated.

The lac operon is a group of genes involved in the metabolism of lactose in E. coli. The lacI gene encodes the lac repressor protein, which binds to the operator region (lacO) and prevents the expression of the lac genes. In the given genotype, lacI+ indicates that the lac repressor is functional, lacP+ indicates that the promoter region is intact, lacOc indicates a constitutive mutation in the operator region, lacZ+ indicates the presence of the β-galactosidase gene, lacY+ indicates the presence of the lactose permease gene, and lacA+ indicates the presence of the transacetylase gene. Since lacOc is a constitutive mutation, it causes the lac operon to be expressed all the time, leading to the high production of β-galactosidase.

The lac operon in E. coli is controlled by the lac I gene, which produces a repressor protein. This repressor protein binds to the operator region of the operon, preventing the transcription of the lac genes. However, in the presence of lactose, the lactose molecules bind to the repressor protein, causing a conformational change that prevents it from binding to the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the lac genes. Therefore, the lac operon control by lac I is an example of negative inducible regulation, as the presence of an inducer (lactose) relieves the repression of the operon.

In negative repressible control, a small molecule is required to bind to the gene's repressor and enable it to bind to DNA, thereby preventing gene expression. This is the opposite of the statement given in the question, which states that the small molecule prevents the gene's repressor from binding to DNA. Therefore, the correct answer is False.

A regulatory gene encodes for a repressor protein, which is a molecule that binds to the operator region of DNA and prevents the transcription of certain genes. This repressor protein helps regulate gene expression by blocking the binding of RNA polymerase to the promoter region, thus inhibiting the initiation of transcription. In this case, the repressor protein is an example of a gene product encoded by a regulatory gene.

If a mutation prevents the formation of the antiterminator 2 + 3 loop in the trp operon, it would result in constitutive attenuation of transcription. The antiterminator 2 + 3 loop is responsible for preventing the termination of transcription in the presence of tryptophan. Without this loop, transcription would be attenuated, meaning it would be prematurely terminated regardless of the presence or absence of tryptophan. This would lead to a constant level of transcription, resulting in constitutive attenuation of transcription.

A possible genotype of the cells could be lacI+ lacP– lacO+ lacZ+ lacY+ lacA+. This genotype suggests that the mutant E. coli strain has a mutation in the lacP gene, which is responsible for the production of the lac repressor protein. Without the lac repressor protein, the lac operon is not properly regulated, leading to the absence of ß-galactosidase production. The other genes (lacI, lacO, lacZ, lacY, lacA) are still functional, allowing for the production of other proteins and enzymes in the lac operon.

An operon is controlled by a repressor, which means that the repressor protein binds to the DNA near the operon and prevents its expression. However, in the case of a negative inducible operon, the repressor is released from binding to the DNA when it binds to a small molecule, such as an inducer. This allows the operon to be expressed and the genes within it to be transcribed. Therefore, if a mutation prevents the repressor from binding to the small molecule, the operon will never be expressed, indicating that it is a negative inducible operon.

The correct answer is that the mutations in P and I are respectively cis and trans acting on lac operon expression. This means that the mutation in P affects the expression of genes on the same DNA molecule, while the mutation in I affects the expression of genes on a different DNA molecule. This suggests that the mutations have different effects on lac operon expression, with the cis mutation likely having a more direct and localized effect, while the trans mutation may have a more indirect and widespread effect.

In a nonmutant E. coli cell that is growing in low glucose and high lactose, the lac repressor would not be bound. The lac repressor is a protein that binds to the lac operator, which is a DNA sequence located upstream of the lac operon. In the presence of lactose, the lac repressor undergoes a conformational change and is unable to bind to the lac operator. This allows for the expression of the lac operon, which includes genes involved in lactose metabolism. In low glucose conditions, the cAMP-CAP complex is formed, which further enhances the expression of the lac operon. Therefore, in the given conditions, the lac repressor would not be bound to the lac operator.