Chapter 12 Sapling Activities

What best defines an operon? a group of bacterial genes that metabolize lactose. a group of bacterial genes that are transcribed together on the same mRNA. a group of bacterial genes that performs a related function. all of the choices. a group of bacterial genes that metabolize any substrate.

a group of bacterial genes that are transcribed together on the same mRNA.

What is a constitutive operon? an operon that can be partially transcribed. an operon with regulated transcription. an operon that is transcribed only some of the time. an operon that is not regulated and is always transcribed.

an operon that is not regulated and is always transcribed.

What is an inducible operon? an operon that is transcribed only during times of extreme stress. an operon that is transcribed when a regulator is bound to it. an operon that is transcribed all the time. an operon that is transcribed when a specific molecule is present.

an operon that is transcribed when a specific molecule is present.

What are characteristics of an enhancer? can regulator transcription of many genes. affects a single gene upstream and downstream of the enhancer. increase transcription of genes. regulates transcription of a single gene. can affect genes great distances away.

can regulate transcription of many genes. increases transcription of genes. can affect genes great distances away.

What are the characteristics of an insulator? limits the effect of an enhancer. part of a gene that helps limit transcription. helps regulate transcription. binds to operator to limit transcription. binds to DNA in order to decrease mutation.

limits the effect of an enhancer. helps regulate transcription.

Determine which of these components may have been altered by mutation to result in a constitutive operon. the operator coding region of the repressor gene the operon promoter the operon coding regions the inducer promoter of the repressor gene

the operator coding region of the repressor gene promoter of the repressor gene

P+lacI^S......P+lacO+lacZ+lacY+lacA+/ P+lacI+...P-lacO^C lacZ+ lacY+lacA+ What would be the result of a partial diploid with a bacterial chromosome containing a super repressor (lacIS) mutation but otherwise wild type, and a plasmid containing a wild- type lacI gene and lacI promoter but also containing both a nonfunctional lac operon promoter mutation and a lacOC mutation? B-galactosidase would only be produced in absence of lactose. B-galactosidase would only be produced in presence of lactose. It is imposible to predict whether or not B-galactosidase will be produced in any condition. B-galactosidase would not be produced whether or not lactose was present. B-galactosidase would always be produced whether or not lactose was present.

B-galactosidase would not be produced whether or not lactose was present.

Which is the role of protein encoded by the lacZ gene? The lacZ gene encodes an enzyme that converts lactose to allolactose, and the lacZ gene encodes an enzyme that converts lactose to glucose and galactose. The lacZ gene encodes an enzyme that permits lactose to enter the bacterial cell. The lacZ gene encodes an enzyme that converts lactose to glucose and galactose. All of the choices are true. The lacZ gene encodes an enzyme that converts lactose to allolactose.

The lacZ gene encodes an enzyme that converts lactose and allolactose, and the lacZ gene encodes an enzyme that converts lactose to glucose and galactose.

What is the operator? The operator is a DNA sequence that binds to the lacI repressor protein. The operator is a protein that sits on the lac operon promoter. The operator is a domain of the lacI repressor that binds to DNA. The operator is an enzyme that converts lactose to allolactose. The operator is the promoter of the lacI gene.

The operator is a DNA sequence that binds to the lacI repressor protein.

The lac operon is inducible. What does this mean? The operon encodes more than one protein. The operon is controlled by a repressor protein. None of the choices are true. The operon is transcriptionally active only in the presence of lactose. The operon is not always transcriptionally active.

The operon is transcriptionally active only in the presence of lactose.

How would mutations cause the operon to be constitutive? The repressor is unable to bind to the operator because a mutation in the repressor gene results in a conformation change. A mutation in the operator region of the operon has altered the binding site of the repressors so that the repressor cannot bind to the operator. A mutation in the repressor results in a conformational change that alters the binding site of the inducer such that the inducer cannot bind to the repressor. A mutation in the promoter region of the repressor gene prevents transcription of the repressor. A mutation in the promoter region of the operon results in a sequence change in the promoter such that transcription always occurs.

The repressor is unable to bind to the operator because a mutation in the repressor gene results in a conformation change. A mutation in the operator region of the operon has altered the binding site of the repressors so that the repressor cannot bind to the operator. A mutation in the promoter region of the repressor gene prevents transcription of the repressor.

Is it possible to get any transcription of the lac operon in the absence of lactose? Why or why not? Yes, cause although the repressor protein keeps transcription at a very low basal level, some transcripts will be produced and translated. Yes, some transcription must take place in order to produce the permeate to allow lactose to enter the cell. Yes, some transcription must take place in order to produce B-galactosidase to make allolactose. Yes, some transcriptase must take place in order to produce the permeate to allow lactose to enter the cell, in order to produce B-galactosidase to make allolactose, and because although the repressor protein keeps transcription at a very low basal level, some transcripts will be produced and translated. No, without lactose the repressor protein will always prevent transcription.

Yes, some transcriptase must take place in order to produce the permeate to allow lactose to enter the cell, in order to produce B-galactosidase to make allolactose, and because although the repressor protein keeps transcription at a very low basal level, some transcripts will be produced and translated.

What is a partial diploid? an operon in combination with its regulatory protein. a bacterium that has one chromosome from its mother and one from its father. a bacterium that has two complete circular chromosomes. a mammalian cell that contains a bacterial artificial chromosome that shares some genes with mammalian chromosomal DNA. a bacterium that has at least some common genes on both the chromosome and a plasmid.

a bacterium that has at least some common genes on both the chromosome and a plasmid.

Select the definition of a repressor. a protein that results in the supercoiling of bacterial DNA so that transcription cannot occur. a regulatory protein that greatly decreases operon transcription by binding to the operator. a section of bacterial DNA that stops operon transcription. a regulatory protein that, when not bound to the operator of an operon, greatly reduces transcription.

a regulatory protein that greatly decreases operon transcription by binding to the operator.

Select the definition of operon. a protein that binds to DNA and controls transcription of related genes. a unit of bacterial DNA that is controlled by a single promoter and encodes related genes. binding site of RNA polymerase in bacteria. a selection of bacterial DNA that controls transcription of related groups of genes.

a unit of bacterial DNA that is controlled by a single promoter and encodes related genes.

What is the inducer of the lac operon? the operator the lacI protein B-galactosidase allolactose lactose

allolactose

Where is the repressor encoded? in a regulatory gene, which is separate from the operon. in the coding region of the operon. in the operator of the operon. the repressor is not encoded by a gene.

in a regulatory gene, which is separate from the operon.

Where might mutations that cause the operon to be constitutively expressed occur? in the repressor gene in the coding region of the operon in the operator region of the operon in the promoter region of the operon in the inducer gene

in the repressor gene in the operator region of the operon

Which of the choices in the most dominant? lacI+ lacO+ lacO^c lacI- lacI^s

lacO^c

Which are the structural genes of the lac operon? lacZ. lacI. lacZ, lacY, and lacA. lacY. lacZ, lacY, lacA, and lacI.

lacZ, lacY, and lacA.

When speaking of gene regulation, regulatory elements are often described as cis- or trans-regulatory elements. A cis-regulatory element is a nucleic acid sequence that regulates the expression of genes located on the same molecule of DNA. In contrast, a trans-regulatory element is a diffusible factor, usually a protein, that may modify gene expression at distant sites on the same or different molecule of DNA. lactose. the lac operator. the lac operon promoter. the lacI repressor. the lacI promoter.

the lacI repressor.