The hormone, also called the ligand is considered as_________.

(a) First messenger

(b) The Second messenger

(c) Both (a) and (b)

(d) None of the above

 

The correct answer is (a) First messenger.

In cell signaling, the hormone or ligand is the initial, extracellular signal that binds to a receptor on the cell's surface. This molecule is always considered the first messenger.

First vs. Second Messengers

The entire process is designed to transmit a signal from the outside of the cell to the inside.

• First Messenger: This is the external signaling molecule (e.g., a hormone like adrenaline) that cannot pass through the cell membrane. It brings the message to the "door" of the cell (the receptor).
• Second Messenger: After the first messenger binds to its receptor, a different molecule is generated inside the cell to continue the signal. This intracellular molecule is the second messenger (e.g., cyclic AMP). Its job is to amplify the signal and spread it throughout the cell, leading to a specific response.

Think of it like a mail delivery: the first messenger is the letter carrier who brings the mail to your house, and the second messenger is the person who opens the letter and tells the rest of the family the news.