Chapter 14

Transcriptional control

inhibition by small RNA molecules, riboswitch blocks initiation, binding of antisense RNA

Select all the conditions that apply in the cell when tryptophan levels are low.

1:2 pause and 3:4 terminator loops do not form, Charged tRNAs are not able to fill both the P site and the A site with the required tryptophan amino acids so translation of the leader peptide stalls, The 2:3 antiterminator loop forms

In attenuation regulation of the trp operon, which stem loop forms when tryptophan is readily available to the cell?

3:4

Select the statements that are true of inducible operons to test your understanding of the differences between inducible and repressible operons.

Inducible operons often contain genes for enzymes that function in catabolic processes., Inducible operons will beturned on in the presence of the substrate and are by default off in its absence., The lac operon is an example of an inducible operon.

CAP binds, repressor is inactive

Lactose present but no glucose

CAP binds, repressor binds

Neither lactose nor glucose present

What is the key factor determining whether or not attenuation will occur when transcription of the E. coli trp operon has been initiated?

The level of trp-tRNA that is charged with tryptophan

Select all of the characteristics that apply to a helix-turn-helix DNA-binding domain.

This DNA-binding domain is found in the lac repressor., The regulatory protein forms a dimer, with each component interacting with a major groove of the DNA., This DNA-binding domain is found in the trp repressor. This DNA-binding domain recognizes and binds to palindromic sequences.

Arabinose is a monosaccharide that E. coli can use as an energy source. When both glucose and arabinose are present in the media, _________.

arabinose binds the repressor, inactivating it, but cAMP levels are low so CAP will not bind to the DNA and transcription does not begin

translational control

attentuation, regulatory protein binds DNA, riboswitch causes termination

The products of the trp operon are expressed _______________ when tryptophan is absent in the media, i.e., the trp repressor is ___________.

continually, inactive

posttraslational control

covalent modification of protein product, feedback inhibition by end product

Constitutive genes

genes expressed continuously by the cell

Housekeeping genes

genes that encode for proteins that are frequently needed by the cell

Inducible genes

genes that encode proteins serving a catabolic function

Repressible genes

genes that encode proteins serving an anabolic function

With the E. coli trp operon where both repression and attenuation occur, the extent of regulation achieved by repression is _________ the extent of regulation achieved by attenuation.

greater than

If lactose is present in the media, the lac repressor is inactivated by binding the ______________, allolactose.

inducer

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

operator

When bound to the DNA, the repressor protein usually prevents attachment of the RNA polymerase to the __________.

promoter

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 tryptophan (trp) operon is an example of negative regulation of a ____________ operon.

repressible

However, if the trp _____________ binds its ________________, tryptophan, transcription stops

repressor, corepressor

In the absence of lactose, the active lac ________________ binds to the lac ___________________.

repressor, operator

Transcriptional riboswitch

riboflavin operon, interrupted mRNA production, FMN as effector, gram-negative bacteria

The E. coli lac operon has ________ operator sequences.

three

In the attenuation mechanism, the 2:3 antiterminator loop can only form because transcription and translation are coupled. This method of transcriptional control could not occur in eukaryotes.

true

If Escherichia coli is cultured in broth containing both glucose and lactose, it _________.

uses glucose preferentially until the supply is exhausted, then uses lactose

Select all of the characteristics that apply to transcriptional riboswitches.

An effector molecule binds directly to the mRNA to terminate transcription., Transcription depends upon the folding pattern of the mRNA mediated by the bound effector., This type of regulation is used by Gram-positive bacteria to regulate amino acid-related genes.

Repressor and CAP are inactive

Both lactose and glucose present

Check the answers that apply to catabolite repression and the lac operon.

CAP is active when bound to cAMP, Adenyl cyclase synthesizes cAMP when glucose levels are low, The lac operon contains a CAP recognition site

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

Catabolite repression

play a critical and indispensable role in central metabolic pathways

Constitutive

CAP is inactive, repressor binds

Glucose present but no lactose

often used in the transport and breakdown of specific energy sources

Inducible

This occurs due to the fact that the formed complex blocks the action of ________________________.

RNA Polymerase

This in turn bends the DNA and inhibits ___________________ action, preventing _________________.

RNA polymerase, transcription

generally used in anabolic (biosynthetic) pathways

Repressible

Select all of the attributes that apply to regulation of translation by small RNA molecules.

Small RNAs can inhibit translation., Small RNAs can promote translation., Small RNAs regulate target RNAs with the Hfq protein., Small RNAs base pair to the leader sequence of a target mRNA.

Which is a false statement regarding riboswitches?

The effector molecules that bind to riboswitches are proteins.

Translational riboswitch

occulusion of Shine-Delgarno site, thiamine biosynthesis operon, ribosome binding inhibition, gram-positive bacteria

If transcription and translation were not coupled in bacteria, what type of regulation would be affected?

Attenuation

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

Attenuation

__________ is used to control transcription of some anabolic pathways involved in amino acid biosynthesis.

Attenuation

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.

How do translational riboswitches and transcriptional riboswitches differ?

Translational riboswitches are mainly observed in Gram-negative bacteria while transcriptional riboswitches are associated with Gram-positive bacteria.

Regulation of transcription by attenuation vs. riboswitches differs in that _________.

attenuation contributes to transcriptional regulation by directing alternative folding of the leader mRNA depending on levels of tryptophan in the cell, whereas riboswitches are nontranslated areas in the leader mRNA that are bound by nonprotein molecules

The __________ is a factor-independent termination site found in the leader region of certain operons, which, under the influence of ribosome behavior, controls the continued transcription of that operon.

attenuator

The lactose (lac) operon is an example of negative regulation of an ________________ operon.

inducible

When a repressor binds to the operator site on the DNA it normally _________.

inhibits the initiation of transcription