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