Chapter 16

A Constitutively expressed gene is _____.

• Repressible

• Always on

•  

  Always off

•  

  Inducible

A mutation prevents repression of the trp operon, maps near the structural genes of the trp operon, and cannot be rescued by adding a wild-type copy of the sequence on a plasmid. Where is this mutation most likely located?

•  

  The operator of the trp operon

•  

  TrpA gene

•  

  The trp operon repressor gene

•  

  TrpE gene

The CAP-cAMP complex is necessary for optimal binding of RNA polymerase in the promoter region of the lac operon. How does the presence of glucose in the cell prevent the CAP-cAMP/promoter interaction when the lac operon is repressed?

•  

  Glucose binds to cAMP, preventing its interaction with CAP.

• Glucose inhibits adenylate cyclase, decreasing the amount of cAMP in the cell.

•  

  Glucose binds to the promoter, preventing its interaction with CAP.

•  

  Glucose binds to CAP, preventing its interaction with cAMP.

What effect does isopropylthiogalactoside (IPTG) have on the lac operon?

•  

  It acts as an inducer of the lac operon and is metabolized by gene products of the lac operon.

•  

  It binds to lactose so that lactose cannot bind to the repressor protein, thus preventing induction of the operon.

•  

  It acts as an inducer of the lac operon, but is not metabolized by the gene products of the lac operon.

•  

  It binds to the promoter region of the lac operon preventing RNA polymerase from binding and preventing transcription of the operon genes.

__________ control is a type of gene regulation in which gene expression occurs unless it is turned off by a regulatory molecule (a repressor).

•  

  Cis-acting

• Positive

•  

  Trans-acting

• Negative

Which of the following molecules helps to "turn off" genes in an operon?

• corepressor

• enhancer

• inducer

• promoter

When taken up by a cell, which of the following molecules binds to a repressor so that the repressor no longer binds to the operator?

• intron

• inducer

• promoter

• corepressor

Which of the following operon types are normally turned on and active?

• Repressible

• Inducible

•  

  Positive control

•  

  Negative control

What happens to the lac operon in the absence of lactose?

•  

  The structural genes within the lac operon will be constitutively transcribed.

•  

  The catabolite activator protein becomes inactivated and no transcription occurs.

•  

  The repressor protein binds to the operator and prevents the transcription of the structural gene.

•  

  The activator protein will be bound to the operator, which will turn on the structural genes behind it.

What is the function of cAMP in regulation of the lac operon?

•  

  It inactivates a repressor protein.

•  

  It activates an activator protein.

• It inactivates a activator protein.

•  

  It activates a repressor protein.