Deck 31: The Control of Gene Expression in Prokaryotes

Question 1

Bacterial cells produce a truncated trp mRNA when cellular levels of tryptophan are __________.

Answer 1

high

Question 2

The pur repressor behaves __________________ to that of the lac repressor.

Answer 2

in an opposite manner

Question 3

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

A) lactose
B) galactose
C) allolactose
D) glucose
E) isopropylthiogalactopyranoside

Answer 3

C

Question 4

Attenuation of the trp mRNA occurs because translation stalls while awaiting the formation of more _______________.

Question 5

What pathway involving phage λ releases approximately 100 viral particles?

A) lysogeny
B) lytic pathway
C) exocytotic pathway
D) attenuation cycle
E) eruption event

Question 6

What type of chemical language allows prokaryotic cells to deduce population densities?

A) quorum sensing
B) colony collapse
C) satellite communication
D) biofilm sensing
E) None of the answers is correct.

Question 7

What name describes the inhibitory effect of glucose, caused by its effect on cAMP levels?

A) glucose repression
B) lactose repression
C) cAMP repression
D) anabolite repression
E) catabolite repression

Question 8

A unit of gene expression that allows controlled and coordinated expression of a set of proteins is called a(n) __________________.

Question 9

In the helix-turn-helix motif of DNA binding proteins, the amino acid side chains of one helix bind to the __________________ and the other to the _________________.

Question 10

What is the name of a peptide containing an abundance of the amino acid residues of the type synthesized by the operon?

A) inhibitory peptide
B) operon peptide
C) leader peptide
D) catabolite peptide
E) regulator peptide

Question 11

What prokaryotic mechanism for regulating transcription is employed by the trp operon?

A) autoinduction
B) constitutive expression
C) catabolite repression
D) attenuation
E) quorum sensing

Question 12

The λ repressor protein blocks transcription of ____________________encoded by the virus.

Question 13

The twofold axis of symmetry of the lac repressor matches the symmetry of the ____________.

Question 14

What substrate forms a colored product in the presence of $\beta$ -galactosidase?

A) p-nitrophenyl galactose
B) Coomassie-galactose
C) ethidium-galactose
D) X-gal
E) None of the answers is correct.

Question 15

What kind of expression governs genes that are expressed at all times?

A) constitutive
B) conservative
C) conscripted
D) consecutive
E) constituent

Question 16

The λ repressor protein promotes transcription of ________________ encoded by the virus when λ repressor levels are relatively low.

Question 17

What compounds are released by one prokaryote to communicate with others in the community?

A) quorum sensors
B) autoinducers
C) biofilms
D) attenuators
E) None of the answers is correct.

Question 18

What is a complex community of prokaryotes?

A) quorum
B) colony
C) satellite
D) leader colony
E) biofilm

Question 19

E. coli is the organism in which many _______________ mechanisms were first discovered.

Question 20

CAP (catabolite activating protein) is an example of a protein that _______________ transcription.

Question 21

What is the binding unit for the methionine repressor?

A) a pair of β strands
B) helix-turn-helix motif
C) zinc finger motif
D) a region with no discernable secondary structure
E) a pair of β strands and zinc finger motif

Question 22

Which of the following is produced when tryptophan levels are low?

A) 162-nucleotide trp mRNA leader sequence
B) 7000-nucleotide trp mRNA
C) 130-nucleotide trp mRNA
D) 162-nucleotide trp mRNA leader sequence and 7000-nucleotide trp mRNA
E) 7000-nucleotide trp mRNA and 130-nucleotide trp mRNA

Question 23

How does the lac repressor find its binding site on DNA?

Question 24

Which of the following conditions leads to the lysogenic state?

A) repressor high, Cro high
B) repressor low, Cro low
C) repressor high, Cro low
D) repressor low, Cro high
E) None of the answers is correct.

Question 25

Which of the following occur in the lytic pathway of bacteriophage infection?

A) Viral particles are released.
B) Viral DNA is not expressed.
C) Viral genome is carried with bacterial replication.
D) Very few viral proteins are produced.
E) None of the answers is correct.

Question 26

Which of the following contributes to the attenuation of the trp mRNA transcript?

A) high levels of tryptophan
B) plentiful amounts of trp tRNA
C) formation of a stem-loop structure at the 5' end of the attenuator region
D) uninterrupted synthesis of the leader peptide
E) All of the answers are correct.

Question 27

In which pathway is the viral genome incorporated into the bacterial DNA?

A) attenuation
B) lysogenic
C) lytic
D) trp operon
E) None of the answers is correct.

Question 28

A chemical commonly used to induce the lac operon in laboratory experiments is

A) lactose.
B) X-Gal.
C) IPTG.
D) galactose.
E) None of the answers is correct.

Question 29

Chemicals released from cells in response to population density and that inhibit gene expression are called

A) autoattenuators.
B) autorepressors.
C) autoinducers.
D) catabolite repressors.
E) None of the answers is correct.

Question 30

Symmetry matching (an inverted repeat) is a common theme in

A) DNA-protein interactions.
B) mRNA modification signals.
C) ribosome binding to DNA.
D) tRNA recognition.
E) None of the answers is correct.

Question 31

Explain the difference between constitutive and regulated expression.

Question 32

How does the inducer affect lac operon regulation?

Question 33

How does the lac repressor inhibit transcription?

A) It binds to the RNA polymerase and prevents its association to the DNA.
B) It binds to the DNA and prevents the RNA polymerase from unwinding and transcribing the DNA.
C) It binds to RNA polymerase and causes a frame shift, thus producing an mRNA with a nonsense mutation.
D) It binds to the mRNA molecule, preventing ribosomes from binding.
E) None of the answers is correct.

Question 34

What is the first step in gene expression control?

A) control of translation
D) control of replication
B) control of mRNA processing
E) None of the answers is correct.
C) control of transcription

Question 35

What reaction is carried out by β-galactosidase?

A) Lactose is hydrolyzed to galactose and sucrose.
B) Lactose is hydrolyzed to galactose and glucose.
C) Lactose is hydrolyzed to two molecules of glucose.
D) Lactose is hydrolyzed to two molecules of galactose.
E) None of the answers is correct.

Question 36

Draw the structure of the lac operon. Identify regions but do not include specific base sequences.

Question 37

What are the elements included in the operon model proposed by Jacob and Monod?

Question 38

The λ repressor has the highest affinity for which of the DNA binding sites?

A) O_R1
B) O_R2
C) O_R3
D) O_R4
E) It has equal affinity for all sites.

Question 39

Many DNA binding proteins, including the CAP and lac repressor, contain a(n) ________ in their structure.

A) pair of β strands
B) helix-turn-helix motif
C) zinc finger motif
D) extensive β-barrel
E) None of the answers is correct.

Question 40

The lac operon contains the gene(s) for the protein(s)

A) β-galactosidase.
B) permease.
C) transacetylase.
D) β-galactosidase and permease
E) All the answers are correct.

Question 41

What are biofilms, and why are they medically important?

Question 42

How does the Cro protein promote the lytic state?

Question 43

Why do many DNA-binding proteins bind as a dimer?

Question 44

What is the relationship between gene regulation and sequences in the genome?

Question 45

How does the λ repressor promote the lysogenic state?

Question 46

How do helix-turn-helix motifs interact with DNA?

Question 47

Describe the proteins that determine whether the lytic or the lysogenic pathway is followed in the infectious cycle of the λ-phage.

Question 48

Briefly explain how attenuation regulates transcription.

Question 49

How was the interaction known as quorum sensing discovered?

Question 50

Is it likely that the DNA binding sites for a repressor evolved from a common ancestor?