genetics ch. 16

According to the crystal structure, to how many lac operator sites does the lac repressor bind at a time? 1 (The lac repressor is a multi-subunit protein capable of binding to more than one site.) 3 (While there are three sites, each of the two dimers within the tetrameric repressor binds to one operator site.) 4 2

2

Why is a merozygote better at complementing a mutation in a trans-acting factor than in a cis-acting element? A trans-acting factor must be adjacent to the gene it is regulating. A cis-acting element must be adjacent to the gene it is regulating. A cis-acting element makes a diffusible product.

A cis-acting element must be adjacent to the gene it is regulating.

How do a corepressor and an inhibitor differ? A corepressor binds directly to the DNA, while an inhibitor binds to the activator protein and prevents it from binding to DNA. (A corepressor binds to a repressor, causing the activated repressor to bind to DNA.) An inhibitor binds to a repressor protein, while a corepressor binds to an activator protein. A corepressor binds to a repressor protein, while an inhibitor binds to an activator protein. A corepressor binds to a repressor protein, thereby causing the protein to bind to the DNA, and an inhibitor binds directly to DNA. (An inhibitor is a protein that binds to another protein, preventing its binding to DNA.)

A corepressor binds to a repressor protein, while an inhibitor binds to an activator protein.

Would using a merozygote better indicate regulation of a gene by a trans-acting factor or a cis-acting element?. Both (A mutation in a cis-acting element is not affected by the introduction of another cis-acting element with normal function into the cell.) A cis-acting element (A mutation in a cis-acting element is not affected by the introduction of another cis-acting element with normal function into the cell.) A trans-acting factor Neither

A trans-acting factor

What effect would either a loss-of-function mutation in the lacI gene or a mutation in operator that prevents repressor binding have? Both result in constitutive expression of the lac operon. Both result in no expression of the lac operon under any circumstance. (The operon cannot be switched off if the repressor is nonfunctional or the operator cannot bind to a functional repressor.) The two mutations would result in completely different phenotypes.

Both result in constitutive expression of the lac operon.

Monod and Jacob studied lactose metabolism in ___ ____

E.coli

How does an effector molecule influence gene expression? The effector molecule binds to a regulatory protein and affects its ability to bind DNA. The effector molecule causes the mRNA to form a stem/loop structure that blocks the ribosome. The effector molecule binds to the mRNA and affects the ability of the ribosome to initiate translation. The effector molecule binds to DNA and affects the ability of RNA polymerase to initiate transcription. (Effector molecules can bind to proteins called activators which then stimulate transcription.)

The effector molecule binds to a regulatory protein and affects its ability to bind DNA.

Why is transcription of the lac operon low when both lactose and glucose are present? Glucose interferes with the production of allolactose. (High levels of glucose lead to low levels of cAMP.) When both lactose and glucose are present, there is not enough ATP to support transcription. The low levels of cAMP result in CAP not binding to the CAP site. The high levels of cAMP result in CAP interfering with the binding of RNA polymerase. (High levels of glucose lead to low levels of cAMP.)

The low levels of cAMP result in CAP not binding to the CAP site.

What type of regulation does not need to be adjacent to the gene(s) it is regulating? Trans-acting factor Cis-acting factor

Trans-acting factor

True or false: The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes. True False (The lac repressor allows low levels of transcription of the lac operon.)

True

In the trp operon, tryptophan acts as. an activator. (tryptophan binding activates the repressor but blocks transcription.) a corepressor. an enzyme. a lone repressor.

a corepressor.

Enzyme adaptation refers to the observation that an enzyme must be present in a cell prior to the cell being exposed to the substrate for that enzyme. a particular substrate appears within a cell only after the cell has been exposed to the enzyme for that substrate. enzymes are always present in cells regardless of whether a substrate is present or absent. a particular enzyme appears within a cell only after the cell has been exposed to the substrate for that enzyme.

a particular enzyme appears within a cell only after the cell has been exposed to the substrate for that enzyme.

An operon is a group of two or more genes under the transcriptional control of a single promoter. different polymerases. two or more promoters.

a single promoter.

A regulatory protein that increases the rate of transcription is a(n)

activator

The observation that a particular enzyme appears within a cell only after a cell has been exposed to the enzyme's substrate is called enzyme ____.

adaption

Cyclic-AMP is a small effector molecule produced by the enzyme ____ ___

adenylyl cyclase

The transport of glucose into a bacterial cell causes the intracellular level of cyclic-AMP to fall because the enzyme ____ ____is inhibited.

adenylyl cyclase

The small effector molecule ___ prevents the lac repressor from binding to the operator site.

allolactose

A regulatory site on a protein where an effector molecule binds is called a(n) ___ site.

allosteric

In the absence of lactose, the lac repressor allows synthesis of β-galactosidase, but not of lac permease. allows very small amounts of the lac enzymes to be made. prevents all transcription of the genes encoding the lac enzymes. (Due to reversible binding of the repressor to the operator, transcription is not completely inhibited.) allows transcription of the lacZ gene but not of the lacA gene.

allows very small amounts of the lac enzymes to be made.

Mutations in the gene for the lac repressor that result in a lac repressor that cannot bind allolactose would mean that transcription from the lac operon is not repressible. (A repressor that cannot bind allolactose will remain bound to the operator, blocking transcription.) induced or repressed normally. always repressed.

always repressed.

The trp operon is regulated by a repressor protein and by ___ in which transcription is stopped prematurely. Listen to the complete question

attenuation

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is _____ _____

catabolite repression

A DNA segment that must be adjacent to the gene(s) it regulates is a___ -____ element.

cis-acting

The probability that allolactose will bind to the lac repressor depends on the allolactose ____ in the bacterial cell.

concentration

If a strain of E. coli has a mutation in the lacI gene such that the lac operon is expressed even in the absence of lactose, the expression is called repressed. constitutive. repressible. (Repressible expression can be switched off.) inducible.

constitutive.

A polycistronic mRNA contains the sequences for several genes and control regions. (Polycistronic mRNA has a single promoter that regulates expression of two or more genes.) contains the sequences for genes from different operons. contains the sequence for only one gene. contains the sequences of two or more genes.

contains the sequences of two or more genes.

The binding of the lac repressor to the operator shuts down transcription from the lac operon when lactose is plentiful in the environment. (When lactose is plentiful, the operon is induced and transcription of the lacZ, lacY and lacA genes occurs.) present in or absent from the environment. depleted from the environment.

depleted from the environment.

The sequential use of sugars by a bacterial cell is called ___ ____

diauxic growth

Many bacterial species use sugars sequentially. This is called catabolite repression. cis-regulation. bacterial conjugation. diauxic growth.

diauxic growth.

The normal lacI gene on the F' factor could rescue the lacI-mutants because the product of the lacI gene encodes a membrane protein. diffusible protein. phospholipid. cis-acting protein. (Cis-acting elements refer to DNA sequences that have effects on adjacent sequences.)

diffusible protein.

The normal lacI gene on the F' factor could rescue the lacI-mutants because the product of the lacI gene encodes a phospholipid. membrane protein. cis-acting protein. (is-acting elements refer to DNA sequences that have effects on adjacent sequences.) diffusible protein.

diffusible protein.

The research of Monod and Jacob that led to the initial understanding of gene regulation stemmed from an interest in the sugar lactose. (The researchers studied the lac operon because it illustrated a specific phenomenon, rather than out of an interest in the sugar lactose.) enzyme adaptation. the amino acid tryptophan.

enzyme adaptation.

Monod, Jacob, and Pardee studied an E. coli strain with a lacI- mutation in which the lac operon was expressed even in the absence of lactose. only when there were very high levels of lactose. (Expression in the presence of high levels of lactose is associated with the I+ genotype.) only in the presence of glucose.

even in the absence of lactose.

The lacA gene encodes the enzyme __ ____

galactoside transacetylase

The enzyme beta-galactosidase cleaves the sugar lactose into ___ and ___

glucose and galactose

In catabolite repression, transcription is influenced by the presence of galactose. fructose. glucose. lactose. ( Catabolite repression is an additional mechanism for regulating the lac operon that does not involve lactose.)

glucose.

The transport of ______ into a cell causes a _______ in the concentration of cyclic-AMP by inhibiting adenylate cyclase. glucose; decrease allolactose; increase tryptophan; increase lactose; decrease

glucose; decrease

Monod, Jacob, and Pardee identified rare E. coli mutants that only grew on sucrose. had abnormal lactose adaptations. only grew on glucose. had rare tryptophan adaptations.

had abnormal lactose adaptations.

When both lactose and glucose are absent from bacterial cells, concentrations of cAMP are high. low. ( Low levels of glucose are associated with high levels of cAMP.) either high or low depending on other factors.

high.

An inducer is a small effector molecule that causes transcription to increase. remain constant decrease.

increase.

When four molecules of allolactose are bound to the lac repressor, the repressor can no longer bind to the operator site, and RNA polymerase is free to transcribe the structural genes of the operon, the operon has been ____

induced

Genes that are regulated by inducers are called ____ genes.

inducible

The ______ gene encodes a repressor protein. lacO lacI lacP lacA lacZ

lacI

Monod and Jacob studied ____ metabolism in E. coli.

lactose

When only ______ is present in bacterial cells, cAMP levels are high. tryptophan lactose glucose (Low levels of glucose are associated with high levels of cAMP.) galactose

lactose

The lacA gene encodes galactoside transacetylase, an enzyme that covalently modifies lactose permease. (Lactose permease is the product of the lacY gene and is not modified by the transacetylase.) CAP. beta-galactosidase. (Beta-galactosidase is the product of the lacZ gene and is not modified by the transacetylase.) lactose.

lactose.

For the lac repressor tetramer to bind two operator sites, a ____ must form in the DNA.

loop

When tryptophan levels in the cell are ______, the trp repressor cannot bind to the _____ site. This allows RNA polymerase to transcribe the genes required for the synthesis of ____ .

low, operator and tryptophan

When both lactose and glucose are present, transcription of the lac operon is low. intermediate. high.

low.

A strain of bacteria containing F' factor genes is called a ____ , or a partial diploid.

merozygote

A protein such as a repressor that inhibits transcription is exerting _____ control of transcription.

negative

Mutations in the gene for the lac repressor that result in a lac repressor that cannot bind DNA would mean that transcription from the lac operon is not repressible. induced or repressed normally. always repressed. (If the lac repressor does not bind to the operator, transcription can occur even in the absence of lactose.)

not repressible.

It has been shown that the lac operon has three ___ sites to which the lac repressor can bind.

operator

When the lac repressor binds to the lac ___site, RNA polymerase cannot transcribe the lacZ, lacY or lacA genes. Listen to the complete question

operator

A loss-of-function mutation in a gene encoding a repressor protein has the same effect as a mutation in the lacY gene lacZ gene operator site. promoter sequence. (A mutation in the promoter sequence would prevent transcription.)

operator site.

A(n)___ is a group of two or more genes under the transcriptional control of a single promoter.

operon

The research of Jacob and Monod provided understanding of the process of translation. our initial understanding of gene regulation. our initial understanding of how transformation occurs. the details pertaining to the structure of DNA. understanding of the process of DNA replication.

our initial understanding of gene regulation.

The lacY gene encodes lactose ____, a membrane protein.

permase

An operon encodes a ____ mRNA, an RNA that contains the sequences of two or more genes.

polycistronic

Transcription regulation by an activator protein is considered to be ______ control. negative (Transcription regulation by a repressor protein is termed negative control.) positive

positive

Allolactose is a small effector molecule that binds to the lac repressor and facilitates the repressor binding to DNA. prevents the repressor from binding to RNA polymerase. (The lac repressor binds to DNA in the operator region.) prevents the repressor from binding to DNA. increases the affinity of the repressor for CAP.

prevents the repressor from binding to DNA.

In an operon, the ______ signals the beginning of transcription. ribosome binding site origin promoter terminator

promoter

The operon is flanked by a ____ that signals the beginning of transcription and a ____ that signals the end of transcription. Listen to the complete question

promoter and terminator

Genes that are regulated by corepressors or inhibitors are called _____ genes.

repressible

A regulatory protein that binds to DNA and inhibits transcription is a(n) ___

repressor

A corepressor is a small molecule that binds to a _____ protein, thereby causing the protein to bind to the DNA, while an inhibitor binds to an ____ protein and prevents it from binding to the DNA.

repressor and activator

An inducer could bind to a(n) ______ and prevent it from binding to the DNA, or it could bind to a(n) ______ and cause it to bind to the DNA. activator; repressor repressor; activator repressor; ribosome activator; polymerase

repressor; activator

The CAP site and the operator site are ______ that function in gene regulation. regulatory RNAs short DNA segments large proteins disaccharides

short DNA segments

When lactose is depleted from the environment, the affinity of allolactose for the repressor increases. (The affinity of allolactose for the repressor is not dependent upon concentration.) the intracellular concentration of allolactose rises. (Allolactose is produced from lactose.) the intracellular concentration of allolactose falls. the affinity of the repressor for DNA decreases.

the intracellular concentration of allolactose falls.

In bacteria, the most common way to regulate gene expression is by influencing the rate of transcription initiation. the rate of transcription elongation. the frequency of cell division. the rate of translation initiation.

the rate of transcription initiation.

The product of the lacY gene is required for covalently modifying lactose and lactose analogs. the transport of lactose into the bacterial cell. converting a small amount of lactose into allolactose. cleaving lactose into glucose and galactose. (Cleavage of lactose is catalyzed by the product of the lacZ gene.)

the transport of lactose into the bacterial cell.

Studies indicate that the lac operon has ______ operator site(s) for the lac repressor. three a single (While mutational analysis first identified a single site, two additional sites were later detected.) dozens of two (While mutational analysis first identified a single site, two additional sites were later detected.)

three

When four molecules of allolactose are bound to the lac repressor, the lac operon is induced, and RNA polymerase transcribes more slowly. is blocked from transcribing any genes. (Transcription occurs when the operon is induced.) transcribes the structural genes of the operon. binds to the operator. (The repressor is a molecule that binds to the operator.)

transcribes the structural genes of the operon.

Experiments by Jacob and Monod demonstrated that enzyme adaptation is due to the regulation of genes during ___

transcription

Select the genes in the trp operon. trpZ trpC trpA trpB trpD trpY trpE

trpC trpA trpB trpD trpE

β-ONPG can be used to detect levels of β-galactosidase, because β-galactosidase cleaves β-ONPG into a substance with a ______ color. yellow blue black green

yellow

Which protein binds to which site? Catabolite activator protein Repressor RNA polymerase Promoter CAP site Operator

Catabolite activator protein-> CAP site Repressor-> Operator RNA polymerase-> Promoter

Monod, Jacob, and Pardee learned about the lac operon using bacterial strains called merozygotes. Since lacI encodes a diffusible protein, in a merozygote, the gene on the ____ ____ could supply the mutant cell with functional repressor protein.

F' factor

True or false: Effector molecules influence gene expression by binding DNA. True (An effector molecule exerts its effects by binding to a repressor or activator.) False

False

The enzyme β-galactosidase is encoded by which gene? LacY LacZ LacA LacO

LacZ

True or false: On a regulatory protein, an allosteric site is the same as the active site. True (An allosteric site is a site other than the active site where effector molecules may bind.) False

False

True or false: The rate of transcription initiation rarely influences overall gene expression. True False

False

What is the name for a strain of bacteria containing an F' factor? Diploid Mutant Heterodimer Merozygote

Merozygote

In the 1950s, ______, ______, and ______ studied mutations in the lac operon of E. coli. Chargaff Watson Monod Pardee Jacob

Monod Pardee Jacob

β-galactosidase activity can be detected using the lactose analog β- ____ because β-glalactosidase cleaves it to a product with a yellow color.

ONPG

A conformational change that prevents the repressor from binding to the lac operator occurs when ___ binds to the lac repressor.

allolactose

The binding of ______ to the lac repressor promotes a conformational change that prevents the repressor from binding to the lac operator. Lac permease allolactose β-galactosidase lactose

allolactose

The intracellular concentration of the inducer ___ remains high as long as lactose is available in the environment.

allolactose

The Lac repressor protein binds to the operator and stops transport of lactose. prevents translation. (The operator is a region in the DNA of the lac operon.) aids RNA polymerase. blocks transcription.

blocks transcription.

The small effector molecule produced by the enzyme adenylyl cyclase is ______. allolactose ATP cAMP β-galactosidase

cAMP

When the Lac repressor is bound to the operator, RNA polymerase ______ the lacZ, lacY, or lacA genes. transcribes one of cannot transcribe increases transcription of

cannot transcribe

When tryptophan levels in the cell are low, the trp repressor ______ bind to the operator site. RNA polymerase ______ transcribe the trp operon. can; cannot (the trp repressor is inactive when tryptophan levels are low) cannot; can can; can cannot; cannot

cannot; can

The somewhat imprecise term that describes how transcriptional regulation is influenced by glucose is ____ ____

catabolite repression

The genes in the trp operon encode only the subunits of the trp repressor protein. regulatory proteins only. enzymes used to metabolize tryptophan in the environment. (The proteins encoded by the trp operon are used to produce the amino acid tryptophan.) enzymes used in tryptophan biosynthesis.

enzymes used in tryptophan biosynthesis.

In attenuation, transcription proceeds half-way through the operon. continues to the transcription stop site. never starts. is stopped prematurely.

is stopped prematurely.

When attenuation occurs, the mRNA is terminated before transcription of the genes required for tryptophan biosynthesis. is transcribed past the attenuator sequence. is transcribed to include the genes required for tryptophan biosynthesis.

is terminated before transcription of the genes required for tryptophan biosynthesis.

Select all of the following that are protein-encoding genes in the lac operon. lacZ lacA lacO (The lacO gene is the operator site. The three protein-encoding genes are lacZ, lacY, and lacA.) lacX lacY

lacZ lacA lacY

The three protein-encoding genes in the lac operon are ____ , ___, and ___.

lacZ, lacY, and lacA

Enzyme adaptation results from the synthesis of specific ______ in response to lactose in the environment. proteins genes sugars

proteins