Cellular signaling follows a cascade of events and has multi

Cellular signaling follows a cascade of events and has multiple points of regulation. Which of the following could be a reason(s) why a signal does not reach its target destination?

A. the ligand was not transported to the correct binding site

B. a chemical modification occurred on serine, threonine, or tyrosine side chains to turn on/off proteins

C. a protein gets tagged with an acetyl group and gets degraded

D. A & B

E. A & C

F. B & C

G. all of the above

Solution

Answer : The correct answer is D (A &B)

Explanation : During signal transduction phenamenan the ligand molecule particularly hormones does not cross the plasmamembrane but binds to receptors and excerts their effects through signaling molecules such as cAMP or cGMP. Down the cascade, phosphorylation of key proteins occurs through the enzymes called protein kinases.

Usually proteins are tagged with ubiquitin for degradation through a proteosomal system.