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: Understand the concept of second messengers.
Second messengers are intracellular signaling molecules that transmit signals from receptors on the cell surface to target molecules inside the cell. They help amplify and regulate cellular responses.

Step 2: Analyze cyclic AMP (cAMP).
Cyclic AMP is one of the most important second messengers in mammalian cells. It is produced from ATP by adenylate cyclase and participates in many signaling pathways. Therefore, option (A) is a second messenger.

Step 3: Analyze diacyl glycerol (DAG).
Diacyl glycerol is generated from membrane phospholipids and acts as a second messenger by activating protein kinase C (PKC). Hence, option (B) is also a second messenger.

Step 4: Analyze calcium ion.
Calcium ion (\(\mathrm{Ca^{2+}}\)) functions as a universal intracellular second messenger and regulates many processes such as muscle contraction, neurotransmitter release, and enzyme activation. Thus, option (C) is a second messenger.

Step 5: Analyze potassium ion.
Potassium ion mainly helps maintain membrane potential and osmotic balance. It is not commonly involved as a second messenger in intracellular signaling pathways. Therefore, option (D) is not a second messenger.

Step 6: Compare all options.
Among the given options, cyclic AMP, diacyl glycerol, and calcium ion are established second messengers, whereas potassium ion is not classified as one.

Step 7: Final conclusion.
Hence, the correct answer is potassium ion.
\[ \boxed{\text{Potassium ion}} \]
Therefore, the correct option is (D).