Ch. 14 Microbiology smartbook

At which of the following operator sites must the lac repressor bind to ensure transcription inhibition?

01

True or false: The trp operon is an example of a positive control system.

False

Transcription initiation of the trp operon is regulated by both ____. alternation trp repressor trp activator ara repressor attenuation

trp repressor attenuation

The nucleotide sequence that encodes the leader sequence of the trp operon is ____.

trpL

The nucleotide sequence that includes the attenuator sequences of the trp operon is ____.

trpL

In the presence of both glucose and lactose, the lactose repressor is not bound to the operator and the genes of the lactose operon are expressed

true

True or false: All catabolite operons are regulated by CAP and a regulatory protein that is specific to each operon.

true Regulation by CAP and a regulatory protein unique to each operon is a common theme for all catabolite operons.

The trp operon is only active when (BLANK) is not present in the cell.

tryptophan/trp

The Lac repressor binds to the lac operon at the position(s) indicated by the letter _____.

B only

Which of the following is NOT a component of bacterial operons? Enhancer Structural genes Operator Promoter

Enhancer

DNA in cells can encode thousands of different proteins. Why do cells require mechanisms to regulate expression of the genes that code for these proteins?

Not all proteins are needed at all times, or in equal amounts. Regulating their expression saves energy and time

Which two of the following describe the catabolite activator protein?

Represses specific operons when glucose is available Activates specific operons when glucose is not available

Which condition is most likely to NOT result in attenuation of transcription of the trp operon?

Slow ribosome activity due to low tryptophan levels

inducers

Small effector molecules whose presence increases the level of specific enzymes are called ____.

In this image of the lac operon, the structural genes are _____.

The lac operon consists of three structural genes—lacZ, lacY, and lacA

In the image (5) of a diauxic growth curve, at time 3 hours, which of the following is true?

The lac operon is repressed.

The trpL operon encodes the leader peptide and (Blank) sequences.

attenuator

Which two proteins are regulators of the lac operon?

lac repressor Catabolite activator protein

The binding of inducer to the lac repressor protein does NOT result in which of the following?

lac repressor binds to operator

When (BLANK) is present in the environment, it is transported into E. coli cells by lactose permease.

lactose

Lactose is transported into the E. coli cell by ____.

lactose permease

When (BLANK) proteins bind to the operator they block the binding of RNA polymerase or inhibit its movement.

repressor

Proteins that inhibit transcription initiation by binding to DNA are called _____.

repressor proteins

Match each bacterial group with their most common use of riboswitches.

- Gram-positive bacteria: Control of transcription -Gram-negative bacteria: Control of translation

The signaling molecule used in quorum sensing by Vibrio fischeri and many other Gram-negative bacteria is ____.

AHL

The adenyl cyclase enzyme converts _____ to cAMP and PPi.

ATP

Regulated genes

Genes that are only expressed when needed

Which two of the following statements about the interaction between the lac repressor and inducer are true? Multiple select question. Inducer binds covalently to the lac repressor. Inducer binding causes repressor to lose ability to bind to the operator sites. Inducer binding recruits the repressor to the operator. Inducer binding changes the repressor shape.

Inducer binding causes repressor to lose ability to bind to the operator sites. Inducer binding changes the repressor shape.

Which two of the following conditions must exist to fully induce the lac operon? Multiple select question. Lack of preferred carbon and energy source Excess of tryptophan Shortage of tryptophan Lactose present in the medium Glucose present in the medium Excess of preferred carbon and energy source

Lack of preferred carbon and energy source Lactose present in the medium

Which statement about the trp operon is true?

Operon is functional when tryptophan is absent.

Which of the following best describes the regulation of the luxI gene in Vibrio fischeri?

Positive autoregulation

Select all that apply Transcription of the trp operon is controlled by which two of the following mechanisms? Multiple select question. Repression of termination by the ribosome Premature termination through attenuation Activator protein enables initiation Repressor protein inhibits initiation

Premature termination through attenuation Repressor protein inhibits initiation

In the regulation of the trp operon of E. coli, when translation does not occur, which of the following happens?

The pause and terminator loops form and transcription stops before RNA polymerase reaches the structural genes of the operon.

True or false: The intracellular level of cAMP depends on the state of a protein that functions in the phosphoenolpyruvate:sugar phosphotransferase system (PTS).

True cAMP levels are linked to the transport and phosphorylation of glucose.

Proteins that promote transcription initiation by binding to DNA are called ____.

activator proteins

DNA-bound activator proteins promote transcription initiation by ____

facilitating RNA polymerase binding

(blank) genes encode enzymes whose level is increased by the presence of small effector molecules.

inducible

Enzymes whose level increases in the presence of small effector molecules are encoded by ____.

inducible genes

This image (5) shows the molecules involved in transcriptional regulation of the lac operon. With the lac repressor and CAP proteins illustrated here, which carbon sources are available?

lactose but no glucose

The lac operon is expressed at high levels when the sugar (BLANK) is available and a preferred source of carbon and energy is lacking.

lactose or allolactose

Vibrio fischeri uses quorum sensing to control the production of

light, bioluminescence, or luciferase

The gene that encodes AHL synthase is called ___

luxl

The mechanism to synthesize cAMP when glucose is absent involves the system for _____.

phosphorylating glucose as it enters the cell

A(n) (blank) protein is a DNA-binding protein that inhibits transcription initiation.

repressor

Which two of the following statements about the inhibition of transcription by the lac repressor protein are true? Multiple select question. Bends the DNA in the promoter region Binds and inhibits RNA polymerase Binds to O1 and one additional lac operator site Degrades the polycistronic message Binds to the O2 and O3 lac operator sites

Bends the DNA in the promoter region Binds to O1 and one additional lac operator site

Which two of the following conditions are required for full activation of the lac operon? High levels of glucose Low levels or absence of glucose Presence of lactose Low levels or absence of lactose

Low levels or absence of glucose Presence of lactose

The transcription of all catabolite operons are regulated by which two of the following?

Regulatory protein specific to the operon Catabolite activator protein

ATP is converted to cAMP by the enzyme

adenyl, adenylyl, or adenylate Cyclase

Binding of an effector to one domain of a transcriptional regulatory protein changes the conformation of its DNA-binding domain. This is an example of _____.

allosteric control

The global control of operons encoding enzymes for the catabolism of carbohydrates that must be modified prior to entering glycolysis is referred to as ____.

catabolite repression

The positive regulatory system called (BLANK) prevents the expression of genes encoding proteins necessary for the utilization of sugars other than glucose when adequate supplies of glucose are present.

catabolite repression

In this image of the trp operon, the repressor protein, indicated by the letter R, binds to the DNA at the _____ site. (image 3)

operator

Proteins that are responsible for the induction or repression of enzyme encoding genes are referred to as (blank) proteins.

regulatory/transcriptional regulatory

Which two of the following statements about the inhibition of transcription by the lac repressor protein are true?

Binds to O1 and one additional lac operator site Bends the DNA in the promoter region

Full transcriptional activation of the lac operon requires high levels of the sugar(BLANK) and low levels or the absence of the sugar (BLANK).

Blank 1: lactose Blank 2: glucose

The inducer for the E. coli lac operon is allolactose produced by the action of permease on lactose.

FALSE - The real inducer for the E. coli lac operon is allolactose produce by the action of beta-galactosidase (B-gal) on lactose.Allolactose binds and inactivates the lac repressor so transcription is no longer inhibited and the lacZ, lac Y, and lac A genes can be transcribed to make enzymes that metabolize lactose.

Which two of the following are mechanisms that can control transcription of the trp operon by way of the attenuator region? Multiple select question. Ribosome stalls in region 1 due to low tryptophan levels - terminator loop forms Ribosome translates at normal speed due to adequate tryptophan levels - antiterminator loop forms Ribosome stalls in region 1 due to low tryptophan levels - antiterminator loop forms Ribosome translates at normal rate due to adequate tryptophan levels - pause and terminator loops are formed

Ribosome stalls in region 1 due to low tryptophan levels - antiterminator loop forms Ribosome translates at normal rate due to adequate tryptophan levels - pause and terminator loops are formed

A regulatory process that results in transcription termination within a leader sequence that precedes the structural genes is termed

attenuation

Termination of transcription elongation before RNA polymerase enters the first structural gene of an operon is called ____.

attenuation

Transcription of the trp operon is regulated at the level of initiation by the trp repressor, and at the level of elongation by a process called

attenuation

Which of the following is not a regulatory mechanism used to control the lactose operon in Escherichia coli?

attenuation

The lac repressor protein inhibits transcription by ____.

bending DNA in the promoter region

When the catabolite activator protein binds to its binding site in DNA, it

bends the DNA

Quorum sensing is used by Vibrio fischeri to control _______.

bioluminescence

DNA-bound repressor proteins inhibit the initiation of transcription by either ____. facilitating the binding of RNA polymerase blocking the binding of RNA polymerase removing RNA polymerase from promoter preventing the movement of RNA polymerase

blocking the binding of RNA polymerase preventing the movement of RNA polymerase

Which cyclic nucleotide activates CAP?

cAMP

Genes that are expressed continuously are called ____.

constitutive genes

Aporepressors are activated by the binding of a(n) ____.

corepressor

For most transcriptional riboswitches, there are two configurations of the leader of an mRNA. What determines the configuration of the leader region?

effector binding to the mRNA

Because the N-acylhomoserine lactone (AHL) moves in and out of the cell by diffusion, cells can sense the local cell density. As the density increases, the external AHL concentration _____ until the concentration gradient is reversed.

increases

The level of some enzymes, such as β-galactosidase, increase significantly in the presence of a small effector molecule called a(n

inducer

For most transcriptional riboswitches, there are two configurations of the mRNA leader region. The configuration is determined by effector binding to the _____.

mRNA leader

The trp operon is best described as an example of the ______.

negative transcriptional control of repressible genes

Bacterial repressor proteins bind to a DNA sequence called the

operator

The site on the DNA to which a repressor protein binds is the __________.

operator

For many years microbial geneticists focused almost exclusively on the regulation of transcription initiation. A likely reason for this is _________.

the process of transcription in microbes was better understood than that of translation

In the trp operon of E. coli, when charged tRNA-Trp is abundant in the cell, the terminator loop forms in the transcript because _____.

the ribosome follows RNA polymerase and efficiently synthesizes the TrpL peptide

Order the following events in the regulation of the trp operon of E. coli when charged tRNA-Trp is abundant in the cell.

1. RNA polymerase initiates transcription at the promoter 2. a ribosome initiates translation of the trpL gene 3. the TrpL peptides synthesized efficiently 4. the terminator loop forms in the transcript 5. RNA polymerase falls off the template 6. translation terminates at a UGA stop codon.

In E.coli regulatory pathways, which molecule functions to ensure that glucose is used as the preferred carbon and energy source?

CAP

Which statement best describes the result of CAP binding to the CAP recognition site?

CAP bends the DNA within two helical turns

This image (6) shows the molecules involved in transcriptional regulation of the lac operon. Considering the lac repressor and CAP proteins illustrated here, which carbon sources are available?

both lactose and glucose

The binding of (BLANK) to the catabolite activator protein causes it to change to the active form.

cAMP, cyclic adenosine monophosphate, cyclic AMP, or cyclic-AMP

In E. coli, the proteins necessary to utilize lactose as an energy and carbon source will not be expressed, even when lactose is present, unless the (2 BLANK) protein is activated by the absence of glucose in the cell. Listen to the complete question

catabolite activator

The lac operon is under the regulatory control of the lac repressor protein, and the (BLANK) protein or CAP.

catabolite activator

Regulation of transcription initiation for the trp operon is accomplished at two levels, 1: transcription initiation by the trp repressor and 2: transcription (BLANK) by the process called attenuation.

elongation

The catabolite activator protein functions in a regulatory network that allows E. coli to preferentially use (BLANK) over all other carbon and energy sources.

glucose

When CAP protein binds to the CAP (blank) site of a catabolite operon, it causes a bend in the DNA which stimulates transcription.

recognition or binding

The trp operon of E. coli is regulated by attenuation. If tryptophan levels are high in the cell, _________.

regions 3 & 4 of the mRNA will base pair and transcription terminates

The genes that encode enzymes that have their expression levels decrease in the presence of pathway end-products are best described as ____.

repressible genes

In the trp operon of E. coli, when there is little charged tRNA-Trp present in the cell, the antiterminator loop forms in the transcript because _____.

the ribosome stalls but the RNA polymerase keeps moving along the transcript

When lactose catabolism is not required, the lac repressor binds to one of (BLANK) different lac operators.

three

Which of the following is the inducer of the lac operon?

Allolactose

In this image (4) of the trp operon, the repressor protein is indicated by the letter R. What is the co-repressor molecule (circled) needed for the repressor protein to be able to bind to DNA?

tryptophan

Lactose is converted to allolactose in the E. coli cell by ____.

β-galactosidase

Order the following events in the regulation of the trp operon of E. coli when there is little charged tRNA-Trp present in the cell.

1. RNA polymerase initiates transcription at the promoter2. A ribosome initiates translation of the trpL gene3. The ribosome stalls, in need of charged tRNA-Trp4. The anti terminator loop forms in the transcript5. RNA polymerase transcribes the structural genes of the trp operon

As a general rule, Gram-negative bacteria use riboswitches to regulate the (BLANK) of mRNA, and Gram-positive bacteria use riboswitches to regulate (BLANK) termination.

Blank 1: translation Blank 2: transcriptional or transcription