Examine the following figure.Imagine that cell signaling using a signal transduction pathway is like a person answering the door after hearing the doorbell ring.Which structure in this figure is like the button for the doorbell?
A) epinephrine
B) the receptor protein
C) proteins of the signal transduction pathway
D) the plasma membrane

Question

Examine the following figure.Imagine that cell signaling using a signal transduction pathway is like a person answering the door after hearing the doorbell ring.Which structure in this figure is like the button for the doorbell? 
A) epinephrine 
B) the receptor protein 
C) proteins of the signal transduction pathway 
D) the plasma membrane

Quizplus · Accepted Answer

The receptor protein is like the button for the doorbell in the signal transduction pathway. Just like how someone has to press the doorbell button for the person inside to hear it and answer the door, a signaling molecule (like epinephrine in this case) binds to the receptor protein, "pressing" the button and initiating the signal transduction pathway inside the cell.

Examine the Following Figure