1. Through genetic engineering, you replace a specific second messenger in a cell’s signaling system with a new second messenger whose molecule has a greatly increased lifetime. How will this change most likely affect the ability of the cell to respond to signaling events that depend on this pathway?

a. Signaling efficiency will be unchanged

b. Signaling will be more efficient unless a negative feedback system is present in the signaling pathway

c.  Signaling through this pathway will be more efficient

d.  Signaling through this pathway will be less efficient

e.  Signaling might be more efficient or less efficient; it depends on whether the steady-state level of the second messenger increases or decreases                                                                                                                                     

2.     While comparing the amino acid sequences of many different GPCRs, you notice the presence of conserved serine and threonine amino acids on the same cytosolic region of each receptor. You change the DNA sequence so that all of the conserved serine and threonine amino acids in the cytosolic region are converted to alanine. Which of the following effects would you most likely see when cells expressing this modified GPCR are exposed to ligand compared to your control cells that do not express the modified GPCR?

a. Cells expressing the modified GPCR will display a reduced response more quickly than control cells.

b. The modified GPCR will be recycled to the cell surface more rapidly than the modified GPCR.

c. The modified GPCR will undergo endocytosis sooner than the unmodified GPCR.

d. The modified GPCR will undergo endocytosis sooner and cells expressing the modified GPCR will display a reduced response more quickly than control cells.

e. Cells expressing the modified GPCR will display a sustained response compared to the control cells.