Question

From the following
$1$ . Catecholamine
$2$ . Inositol $1,4,5$ -triphosphate
$3$ . cAMP
$4$ . Adenylyl cyclase
Which of the above is/are second messengers?

• A. $1,3$ and $4$
• B. $2$ and $3$ only
• C. $1$ and $3$ only
• D. $1,2,3$ and $4$

Answer 1

Answer: (B)

Amino-acid derivatives (epinephrine and nor-epinephrine) and peptide hormones (insulin, glucagon, gonadotropins, etc.) have receptors attached to the cell membrane. Hormones which interact with membrane-bound receptors normally do not enter the target cell, but generate second messengers (e.g., cyclic AMP, IP₃, Ca⁺² etc.) which in turn regulate cellular metabolism.
Adenylyl cyclase: This enzyme is coupled with G-protein receptor. On binding with the amino-derived hormones (e.g. adrenaline, nor-adrenaline etc.) it catalyzes the conversion of ATP to cAMP (secondary messenger).
Adrenaline and nor-adrenaline are commonly called catecholamines.