Engineering Questions with Answers - Multiple Choice Questions

MCQs on Cell Signaling and Signal Transduction – Role of NO

1 - Question

Nitric oxide is an intracellular messenger.
a) True
b) False

View Answer

Answer: a
Explanation: In 1980s, it was discovered that nitric oxide, a gas, acts as an intracellular messenger. NO is unusual because it acts both as an extracellular messenger driving the intracellular responses and also as a secondary messenger in the cell where it is generated.




2 - Question

Nitric oxide is formed from which of the amino acid?
a) L-lysine
b) R-lysine
c) R-arginine
d) L-arginine

View Answer

Answer: d
Explanation: Nitric oxide is formed from the amino acid L-arginine in a reaction catalyzed by nitric oxide synthase (NOS) that requires oxygen and NADPH. Nitric oxide is involved in many biological processes.




3 - Question

. Acetylcholine has the function of ________________________
a) muscle relaxation
b) fertilizing agent
c) promoting cell adhesion
d) promoting cell division

View Answer

Answer: a
Explanation: Acetylcholine has the function of promoting muscle relaxation. It binds to surface receptors present on the endothelial cells leading to the production and release of an agent that diffuses through the plasma membrane and causes the muscles to relax.




4 - Question

The diffusible agent produced by binding of acetylcholine to endothelial cells is __________________
a) vimentin
b) nitric oxide
c) hydrogen peroxide
d) hydrogen sulfide

View Answer

Answer: b
Explanation: In 1986, it was discovered Louis Ignarro at UCLA and Salvador Moncada at the Wellcome Research Labs in England that the diffusible compound produced by the binding of acetylcholine to endothelial cells is nitric oxide.




5 - Question

. Binding of acetylcholine to outer surface of endothelial cells, signals _____________________
a) increase in cytosolic Ca2+ concentration
b) decrease cytosolic Ca2+ concentration
c) increase in acidity
d) increase in basicity

View Answer

Answer: a
Explanation: Binding of acetylcholine to the outer surface of endothelial cells signals an elevation of cytoplasmic concentration of calcium ions, that activates the enzyme nitric oxide synthase.




6 - Question

The nitric oxide binds to and stimulates guanylyl cyclase.
a) True
b) False

View Answer

Answer: a
Explanation: The nitric oxide produced in the endothelial cells diffuses through the plasma membrane and into the adjoining smooth muscle cells. There it binds to and stimulates the guanylyl cyclase.




7 - Question

Which of the following compounds is metabolized into nitric oxide?
a) Phosphoglycerine
b) Nitroglycerine
c) Sulforaphane
d) Serotonin

View Answer

Answer: b
Explanation: Nitroglycerine is metabolized into nitric oxide which stimulates the relaxation of smooth muscle cells. Nitroglycerine is used to treat the pain of angina – chest pain caused to reduced blood flow to the heart.




8 - Question

The development of Viagra is related to the discovery of nitric oxide as a ____________________
a) secondary messenger
b) gaseous compound
c) primary messenger
d) cyclin inhibitor

View Answer

Answer: a
Explanation: The development of Viagra (sildenafil) is based on the discovery of nitric oxide as a secondary messenger. During sexual arousal, the nerve endings of penis release NO which causes relaxation of smooth muscle cells in lining of penile blood vessels and engorgement of penis with blood.




9 - Question

Viagra is specific for which isoform of cGMP phosphodiesterase?
a) PDE2
b) PDE4
c) PDE5
d) PDE8

View Answer

Answer: c
Explanation: Cyclic guanosine monophosphate (cGMP) phosphodiesterase is the enzyme that destroys cyclic guanosine monophosphate. Viagra inhibits the particular isoform PDE5 of the enzyme.




10 - Question

The posttranslational modification involving nitric oxide is called __________________
a) N-nitrosylation
b) P-nitrosylation
c) N-glycosylation
d) S-nitrosylation

View Answer

Answer: d
Explanation: The posttranslational modification wherein nitric oxide (NO) is covalently added to the thiol group of a protein cysteine residue (S-NO) is called S-nitrosylation. This modification alters the activity and interactions of the protein.

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