Question

Which one of the following is NOT a second messenger in mammalian cells?

• A. Cyclic AMP
• B. Diacyl glycerol
• C. Calcium ion
• D. Potassium ion

Hint:

Common second messengers in mammalian cells include cAMP, cGMP, IP\(_3\), DAG, and \(\mathrm{Ca^{2+}}\).

Answer 1

The Correct Option is D

Step 1: What counts as a second messenger.
A second messenger is a small molecule made inside the cell that carries a signal onward after a receptor is switched on. Classic examples build up fast and then fade.

Step 2: Check cyclic AMP and DAG.
Cyclic AMP is made from ATP and triggers many pathways. Diacyl glycerol comes off the membrane and turns on protein kinase C. Both are textbook second messengers.

Step 3: Check calcium.
Calcium ions flood in or get released from stores to drive muscle contraction, secretion and enzyme switching. So calcium also fits the role.

Step 4: Look at potassium.
Potassium ions mainly set the resting voltage of the membrane and keep water balance steady. They do not act as a relay molecule in a signalling cascade.

Step 5: Answer.
The odd one out is potassium ion. \[ \boxed{\text{Potassium ion}} \]