Apex-ANS Exam 2026/2027 – Questions,
Correct Answers & Explanations
Put the signal transduction events in order:
G protein
1st messenger
Effector
2nd messenger - correct answer-1. 1st messenger
2. G protein
3. Effector
4. 2nd messenger
Signal transduction describes the process where an extracellular stimulus initiates
an intracellular response .
Epinephrine (first messenger) binds to the beta-1 receptor (G protein) in the
cardiac myocytes membrane. The beta-1 receptors (G-protein) activates an
effector enzyme (adenylate cyclase), & this effector enzyme activates the second
messenger (cAMP).
The second messenger (cAMP) initiates a series of phosphorylation reactions that
ultimately increase intracellular calcium, leading to a stronger force of
contraction. At the same time, these phosphorylation reactions also activate the
Ca+2ATPase on the sarcoplasmic reticulum, which improves lusitropy by
,enhancing calcium uptake back into the SR . This is how epinephrine
simultaneously improves, myocardial contractility and relaxation.
Which enzyme is represented in the Gq pathway?
A. Adenylate cyclase
B. Phospholipase C
C. Guanylate cyclase
D. Phosphodiesterase - correct answer-B. Phospholipase C
Alpha-1 receptor, vasopressin-1, histamine-1, muscarinic-1, & muscarinic-3 all are
GQ pathway.
Example alpha-1 receptor :
First messenger : phenylephrine norepinephrine
Receptor: alpha-1
Effector enzyme : phospholipase C
Second messenger : IP3, DHG, & Ca+2
Which enzyme deactivates cAMP?
A. Phosphodiesterase.
B. Phospholipase C
C. COMT
D. Protein kinase A - correct answer-A. Phosphodiesterase
, Beta-1 receptors are present in the heart and Beta-2 receptors are present in the
vasculature. Activation of these receptors converts ATP to cAMP inside the cell.
cAMP is responsible for turning on a variety of protein kinases that instruct the
cell to perform a specific function. Remember that a second messengers function
is cell specific; it does different things in different cell types.
Phosphodiesterase hydrolyzes cAMP to AMP. In essence, this turns off the protein
kinases and instructs the cell to stop that specific function. By inhibiting the turn
off mechanism, phosphodiesterase inhibitor's increase cAMP.
In the case of a beta-1 receptor, PDEIs increase intracellular calcium, an increase
inotropy.
In the case of the beta-2 receptor, PDEIs decrease intracellular calcium and cause
vasodilation
Stimulation of which muscarinic receptors are inhibits adenylate cyclase?
A. M1
B. M2
C. M3
D. M5 - correct answer-B. M2
Even numbered muscarinic receptors, M2 & M4, inhibit adenylate cyclase. (Gi)
Odd numbered muscarinic, receptors M1, M3, and M5 stimulate phospholipase.
(Gq)
Match each enzyme with its primary function in catecholamines synthesis:
Tyrosine hydroxylase
Dopamine beta-hydroxylase
Correct Answers & Explanations
Put the signal transduction events in order:
G protein
1st messenger
Effector
2nd messenger - correct answer-1. 1st messenger
2. G protein
3. Effector
4. 2nd messenger
Signal transduction describes the process where an extracellular stimulus initiates
an intracellular response .
Epinephrine (first messenger) binds to the beta-1 receptor (G protein) in the
cardiac myocytes membrane. The beta-1 receptors (G-protein) activates an
effector enzyme (adenylate cyclase), & this effector enzyme activates the second
messenger (cAMP).
The second messenger (cAMP) initiates a series of phosphorylation reactions that
ultimately increase intracellular calcium, leading to a stronger force of
contraction. At the same time, these phosphorylation reactions also activate the
Ca+2ATPase on the sarcoplasmic reticulum, which improves lusitropy by
,enhancing calcium uptake back into the SR . This is how epinephrine
simultaneously improves, myocardial contractility and relaxation.
Which enzyme is represented in the Gq pathway?
A. Adenylate cyclase
B. Phospholipase C
C. Guanylate cyclase
D. Phosphodiesterase - correct answer-B. Phospholipase C
Alpha-1 receptor, vasopressin-1, histamine-1, muscarinic-1, & muscarinic-3 all are
GQ pathway.
Example alpha-1 receptor :
First messenger : phenylephrine norepinephrine
Receptor: alpha-1
Effector enzyme : phospholipase C
Second messenger : IP3, DHG, & Ca+2
Which enzyme deactivates cAMP?
A. Phosphodiesterase.
B. Phospholipase C
C. COMT
D. Protein kinase A - correct answer-A. Phosphodiesterase
, Beta-1 receptors are present in the heart and Beta-2 receptors are present in the
vasculature. Activation of these receptors converts ATP to cAMP inside the cell.
cAMP is responsible for turning on a variety of protein kinases that instruct the
cell to perform a specific function. Remember that a second messengers function
is cell specific; it does different things in different cell types.
Phosphodiesterase hydrolyzes cAMP to AMP. In essence, this turns off the protein
kinases and instructs the cell to stop that specific function. By inhibiting the turn
off mechanism, phosphodiesterase inhibitor's increase cAMP.
In the case of a beta-1 receptor, PDEIs increase intracellular calcium, an increase
inotropy.
In the case of the beta-2 receptor, PDEIs decrease intracellular calcium and cause
vasodilation
Stimulation of which muscarinic receptors are inhibits adenylate cyclase?
A. M1
B. M2
C. M3
D. M5 - correct answer-B. M2
Even numbered muscarinic receptors, M2 & M4, inhibit adenylate cyclase. (Gi)
Odd numbered muscarinic, receptors M1, M3, and M5 stimulate phospholipase.
(Gq)
Match each enzyme with its primary function in catecholamines synthesis:
Tyrosine hydroxylase
Dopamine beta-hydroxylase
