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.

TLS Online TPP Program

#Question id: 1723

#Unit 4. Cell Communication and Cell Signaling

Which of the following statements is the single best description of the location where adaptive immune responses arise?

TLS Online TPP Program

#Question id: 1724

#Unit 4. Cell Communication and Cell Signaling

Which of the following statements is the single best defining characteristic of a follicular dendritic cell (FDC)?

TLS Online TPP Program

#Question id: 1725

#Unit 4. Cell Communication and Cell Signaling

What is the single cell type most characteristically associated with the mucosa-associated lymphoid tissue (MALT)?

TLS Online TPP Program

#Question id: 1726

#Unit 4. Cell Communication and Cell Signaling

What is CD8 a marker of?

TLS Online TPP Program

#Question id: 1727

#Unit 4. Cell Communication and Cell Signaling

Which of the following statements is TRUE of CD4?

TLS Online TPP Program

#Question id: 1728

#Unit 4. Cell Communication and Cell Signaling

Which of the following is characteristic of B- but not T-cells?