Lac operon

What is the function of a polyribosome in both bacteria and eukaryotes?

• Facilitate the transport of mRNA out of the nucleus

• Regulate the expression of constitutive genes

• Prevent transcription and translation from occurring simultaneously

• Enable a cell to make many copies of a polypeptide very quickly

Answer explanation

Polyribosomes enable a cell to make many copies of a polypeptide very quickly, functioning in both bacteria and eukaryotes.

What is a key difference between bacterial and eukaryotic protein synthesis?

• Bacterial protein synthesis undergoes RNA splicing

• Eukaryotic protein synthesis is not modified before translation

• Eukaryotic protein synthesis is translated as soon as it is transcribed

• Bacterial protein synthesis must be transported out of the nucleus first for translation

Answer explanation

Eukaryotic protein synthesis is translated as soon as it is transcribed, unlike bacterial protein synthesis which requires transport out of the nucleus first.

What is the function of the operator in an operon?

• Controls transcription of structural genes by allowing or preventing RNA polymerase binding to the promoter

• Codes for the production of repressor protein

• Facilitates the transport of mRNA out of the nucleus

• Initiates the translation process in bacteria

Answer explanation

The operator controls transcription of structural genes by allowing or preventing RNA polymerase binding to the promoter, regulating gene expression in an operon.

What happens when lactose is absent in the lac operon?

• Allolactose binds to the lac repressor, activating the lac operon

• The lac repressor is inactivated, allowing transcription of lac genes

• The lac repressor binds to the lac operator, blocking transcription of lac genes

• RNA polymerase binds to the lac promoter, initiating transcription of lac genes

Answer explanation

When lactose is absent, the lac repressor binds to the lac operator, preventing transcription of lac genes. This is how the lac operon is regulated in the absence of lactose.

What is the role of allolactose in the lac operon?

• Facilitates the translation of structural genes in bacteria

• Binds to the lac repressor, inactivating it and derepressing the lac operon

• Codes for the production of permease enzyme

• Blocks the lac promoter, preventing transcription of lac genes

Answer explanation

Allolactose binds to the lac repressor, inactivating it and derepressing the lac operon, allowing for the transcription of lac genes.

What is the primary function of the lac Z gene in the lac operon?

• Codes for transacetylase, an enzyme that detoxifies other molecules

• Codes for the production of repressor protein

• Codes for permease, the membrane protein that transports lactose into the cell

• Codes for β-galactosidase, which hydrolyzes lactose into glucose and galactose

Answer explanation

The lac Z gene in the lac operon codes for β-galactosidase, which hydrolyzes lactose into glucose and galactose, making it the primary function of the gene.

What is the mechanism of the lac operon when lactose is present?

• The lac repressor is inactivated, preventing transcription of lac genes

• The lac repressor binds to the lac operator, blocking transcription of lac genes

• Allolactose binds to the lac repressor, altering its shape and allowing RNA polymerase to bind to the promoter

• RNA polymerase is inhibited from binding to the lac promoter

Answer explanation

The correct mechanism of the lac operon when lactose is present involves allolactose binding to the lac repressor, altering its shape and allowing RNA polymerase to bind to the promoter.

What is the conclusion about the lac operon based on its mechanism?

• The lac operon is a repressible system that stops producing proteins in the presence of lactose

• The lac operon is a constitutive system that constantly expresses proteins

• The lac operon is a regulatory system that controls the translation of structural genes

• The lac operon is an inducible system that switches on in the presence of a specific small molecule

Answer explanation

The correct conclusion about the lac operon based on its mechanism is that it is an inducible system that switches on in the presence of a specific small molecule.

What is the definition of an operon?

• A small molecule that binds to a bacterial repressor protein and changes its shape

• A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a cluster of genes

• A specific nucleotide sequence of DNA where RNA polymerase binds to initiate translation

• A regulatory region that controls the expression of structural genes in eukaryotes

Answer explanation

An operon is a unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a cluster of genes. This choice accurately describes the definition of an operon.

What is the primary function of structural genes in an operon?

• Facilitate the transport of mRNA out of the nucleus

• Initiate the translation process in bacteria

• Code for the production of repressor protein

• Code for a group of enzymes with related function

Answer explanation

Structural genes in an operon code for a group of enzymes with related function, playing a key role in the production of specific proteins within the operon.