Imagine that you have created a fusion between the Trp operon, which encodes the enzymes for tryptophan biosynthesis, and the Lac operon, which encodes the enzymes necessary for lactose utilization. Under which set of conditions (A–F below) will β-galactosidase be expressed in the strain that carries the fused operon?

A. Only when lactose and glucose are both absent.

B. Only when lactose and glucose are both present.

C. Only when lactose is absent and glucose is present.

D. Only when lactose is present and glucose is absent.

E. Only when tryptophan is absent.

F. Only when tryptophan is present.

#Question id: 3978

#Unit 3. Fundamental Processes

The 5'-terminal cap structure of eukaryotic mRNAs is a(n):

#Question id: 3979

#Unit 3. Fundamental Processes

“Housekeeping genes” in bacteria are commonly expressed constitutively, but not all of these genes are expressed at the same level (the same number of molecules per cell).  The primary mechanism responsible for variations in the level of constitutive enzymes from different genes is that:

#Question id: 3980

#Unit 3. Fundamental Processes

Which of the following statements correctly describes promoters in E. coli?

#Question id: 3981

#Unit 3. Fundamental Processes

The diagram below represents a hypothetical operon in the bacterium E. coli.  The operon consists of two structural genes (A and B), which code for the enzymes A-ase and B-ase, respectively, and also includes P (promoter) and O (operator) regions as shown.

 When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes A-ase and B-ase are both synthesized at a 50-fold higher rate than in the absence of X.  (X has a molecular weight of about 200.)  Which of the following statements is true of the operon decribed above?

#Question id: 3982

#Unit 3. Fundamental Processes

The diagram below represents a hypothetical operon in the bacterium E. coli.  The operon consists of two structural genes (A and B) that code for the enzymes A-ase and B-ase, respectively, and also includes P (promoter) and O (operator) regions as shown.

 When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes A-ase and B-ase are both synthesized at a 50-fold higher rate than in the absence of X (which has a molecular weight of about 200).  Which one of the following statements is true of such an operon?

#Question id: 3983

#Unit 3. Fundamental Processes

Transcription of the lactose operon in E. coli is stimulated by: