Question

Which of these is a second messenger?
A. ATP
B. cAMP
C. GTP
D. ATP and AMP

Answer 1

The signals are transferred from receptors to target molecules inside the cell. The receptors are present on the cell surface. The molecules which help in transferring the signals are called second messengers.

Complete answer:
Second messengers are the intracellular signalling molecules and they are short-lived. There are three types of second messengers.
1.Hydrophobic
2.Hydrophilic
3.Gases
Diacylglycerol and Phosphatidylinositols are Hydrophobic.(Inositol triphosphate)
cAMP, cGMP are Hydrophilic. (cyclic nucleotides)
NO and CO are gases.

Option A: ATP: Adenosine triphosphate is the energy currency of the cell. As the name suggests, it is made of three groups of phosphate and molecule adenosine. It is the end process of phosphorylation, fermentation and respiration. When ATP is hydrolyzed, ADP is formed. It also helps in transferring signals but it is not a second messenger. Therefore, this is the incorrect option.

Option B: cAMP: Cyclic AMP is formed from ATP by the action of enzyme. Changing the molecular activities in the cytosol, uses PKC (protein kinase A). It is a second messenger. Several hormones affect the cyclic AMP. Therefore, this is the correct option.

Option C: GTP: Guanosine triphosphate, it is similar to DNA and helps in protein synthesis. It is not a second messenger. Therefore, this is the incorrect option.

Option D: ATP and AMP: Adenosine monophosphate, it is a nucleotide and helps in synthesis of RNA. Sometimes it also exists in cyclic forms called cAMP. Therefore, this is the incorrect option.

Hence, the correct answer is option (B)

Note: Second messengers activate signalling pathways. These then amplify the signal. It helps in development of the nervous system. They are highly interactive. Various hormones, growth factors and neurotransmitters.