CHAP 16 RQ - Genetics

What effect would a loss-of-function mutation in the lacI gene and a mutation in operator that prevents repressor binding have?

Both result in constitutive expression of the lac operon.

T or F: Effector molecules influence gene expression by binding to DNA

False

T or F: the rate of transcription initiation rarely influences overall gene expression

False

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

NEGATIVE control

An operon encodes a(n) ____ mRNA, an RNA that contains the sequence of two or more genes

POLYCISTRONIC mRNA

transcription regulation by an activator is considered to be ____ control

POSITIVE control

How does an effector molecule influence gene expression?

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?

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

What type of regulator does not need to be adjacent to the gene(s) it is regulating?

Trans-acting factor

True or false: The lac repressor does not completely inhibit transcription of the lacZ, lacY, and lacA genes.

True

How do a corepressor and an inhibitor differ?

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

Enzyme adaptation refers to the observation that

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

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 ____

adaptation

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 binding of ______ to the lac repressor promotes a conformational change that prevents the repressor from binding to the lac operator.

allolactose

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

allolactose

The small effector molecule that prevents the lac repressor from binding to the operator site is _________

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 very small amounts of lac operon enzymes to be made

Consider a mutation in the gene for the lac repressor that prevents the protein from binding allolactose. Due to this mutation, transcription from the lac operon would ______

always be repressed

What do you call an RNA strand that is complementary to an mRNA molecule?

antisense RNA

The trp operon is regulated by a repressor protein and by _________, in which transcription is stopped prematurely.

attenuation

The lac repressor protein binds to the operator and ______

blocks transcription

During attenuation, transcription begins ______

but is terminated before the entire mRNA is made

The small effector molecule produced by the enzyme adenylyl cyclase is ______

cAMP

When the lac repressor is bound to the operator, RNA polymerase ______ the lacZ, lacY, or lacA genes.

cannot transcribe

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

Antisense RNA is an RNA strand that is ________ to an mRNA molecule

complementary

The binding of a small effector molecule to a regulatory protein changes the ________ of the regulatory protein, which alters its DNA-binding ability.

conformation

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 ______.

constitutive

Posttranslational regulation refers to ______

control of proteins already in the cell

The binding of the lac repressor to the operator shuts down transcription from the lac operon when lactose is ______ the environment.

depleted from

The genes in the trp operon encode ______

enzymes used in tryptophan biosynthesis

True or false: On a regulatory protein, an allosteric site is the same as the active site

false

Consider a case where the end product of a metabolic pathway inhibits an enzyme that acts early on in the pathway. This mechanism of regulation is called ________ ________

feedback inhibition

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

galactose; glucose

In catabolite repression, transcription is influenced by the presence of ______

glucose

The transport of ______ into a cell causes a(n) _______ in the concentration of cyclic-AMP by inhibiting adenylate cyclase

glucose; decrease

When both lactose and glucose are absent from bacterial cells, concentrations of cAMP are ______

high

When tryptophan levels in the cell are _____, translation of the trpL mRNA continues to its stop codon, which terminates further transcription of the operon.

high

An inducer is a small effector molecule that causes the rate of transcription to ____

increase

The binding of four molecules of allolactose to the lac repressor prevents the repressor from binding to the operator site. RNA polymerase is therefore free to transcribe the structural genes of the lac operon, and so the operon is said to be ___________

induced

Genes that are regulated by inducers are called ___________ genes.

inducible

In attenuation, transcription ______

is stopped prematurely

The enzyme β-galactosidase is encoded by which gene?

lac Z

Which of the following are protein-encoding genes in the lac operon?

lacA, lacZ, lacY

The ______ gene encodes a repressor protein.

lacl

When only ______ is present in bacterial cells, cAMP levels are high

lactose

When both lactose and glucose are present, transcription of the lac operon is ______

low

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, tryptophan (trp)

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

When the lac repressor binds to the lac ________ site, RNA polymerase cannot transcribe the lacZ, lacY, and lacA genes

operator

A loss-of-function mutation in a gene encoding a repressor protein has the same effect as a mutation in the ______

operator site

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

operon

The lacY gene encodes lactose ________ a membrane protein

permease

Control of proteins already present in the cell is called ________ regulation

posttranslational

Allolactose is a small effector molecule that binds to the lac repressor and ______

prevents the repressor from binding to DNA

In an operon, the ____ signals the beginning of transcription

promoter

The operon is flanked by a sequence called a(n) ____ that signals the beginning a transcription and one termed a(n) ____ that signals the end of transcription

promoter; terminator

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

proteins

In bacteria, the most common way to regulate gene expression is by influencing the ____

rate of transcription initiation

in bacteria, the most common way to regulate gene expression is by influencing the ____

rate of transcription initiation

Genes that are regulated by corepressors or inhibitors are called ________ genes

repressible

A regulatory protein that binds to DNA & inhibits transcription is called a(n) ____

repressor

a regulatory protein that binds to DNA and inhibits transcription is called a(n) ____

repressor

A corepressor is a small molecule that binds to a(n) ____ protein, thereby causing the protein to bind to the DNA. On the other hand, an inhibitor binds to a(n) ____ protein and prevents it from binding to the DNA.

repressor; 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.

repressor; activator

A translational repressor protein may bind to the mRNA and ______

stabilize a secondary structure that prevents translation

The mRNA from the trpL gene has four regions that are complementary to each other and cause the mRNA to form ______ _____

stem loops

When attenuation occurs in the trp operon, the mRNA is ______

terminated before transcription of the genes required for tryptophan biosynthesis

When lactose is depleted from the environment, the _______

the intracellular concentration of allolactose falls

The product of the lacY gene is required for ______.

the transport of lactose into the bacterial cell

When four molecules of allolactose are bound to the lac repressor, the lac operon is induced, and RNA polymerase ______

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

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

transcription

What genes are in the trp operon?

trpD, trpE, trpB, trpA, trpC

The mRNA made from the ______ gene contains codons for 14 amino acids that form the trp leader peptide

trpL

A polycistronic mRNA contains the sequence(s) for ______.

two or more genes