This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cell Signaling and Signal Transduction – Role of NO”.
1. Nitric oxide is an intracellular messenger.
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. Nitric oxide is formed from which of the amino acid?
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. Acetylcholine has the function of ________________________
a) muscle relaxation
b) fertilizing agent
c) promoting cell adhesion
d) promoting cell division
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. The diffusible agent produced by binding of acetylcholine to endothelial cells is __________________
b) nitric oxide
c) hydrogen peroxide
d) hydrogen sulfide
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. 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
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. The nitric oxide binds to and stimulates guanylyl cyclase.
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. Which of the following compounds is metabolized into nitric oxide?
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. 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
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. Viagra is specific for which isoform of cGMP phosphodiesterase?
Explanation: Cyclic guanosine monophosphate (cGMP) phosphodiesterase is the enzyme that destroys cyclic guanosine monophosphate. Viagra inhibits the particular isoform PDE5 of the enzyme.
10. The posttranslational modification involving nitric oxide is called __________________
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.
Sanfoundry Global Education & Learning Series – Cell Biology.
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