This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Non-muscle Motility – 1”.
1. Cortex (of a cell) is located beneath the _____________
a) nucleus
b) mitochondria
c) ribosomes
d) plasma membrane
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Explanation: Cortex of a cell is located just beneath the plasma membrane. It is an active region of the cell that participates in ingestion of extracellular materials, cell division and motility.
2. Which type of cytoskeletal elements are involved in nonmuscle motility?
a) microfilaments
b) flagella
c) intermediate filaments
d) microtubules
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Explanation: Microfilaments primarily constitute the cortex of a cell and aid in the process of cell motility. All the associated process depends on the assembly of microfilaments in the cortex.
3. Nucleation is the slowest step in actin filament formation.
a) True
b) False
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Explanation: The slowest step in the formation of actin filaments is nucleation. At least two or three actin monomers come together in proper orientation in this step.
4. Which of the following nucleating protein generates unbranched actin filaments?
a) formin
b) kinesin
c) globulin
d) vimentin
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Explanation: Formin is a nucleating protein that helps in the nucleation of actin filaments. It helps in the generation of unbranched filaments such as those found in focal adhesions.
5. Which of the following binds to G-actin?
a) thymosin
b) lysin
c) kinesin
d) chymosin
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Explanation: Thymosins are the proteins that bind to G-actin and prevent their polymerization. Actin-ATP monomers are referred to as G-actin.
6. Monomer-sequestering proteins are responsible for high concentration of G-actin in nonmuscle cells.
a) True
b) False
View Answer
Explanation: Monomer-sequestering proteins such as thymosin β4 are responsible for high concentration of G-actin in nonmuscle cells.
7. Tropomodulin is a ___________
a) monomer-sequestering protein
b) capping protein
c) monomer unit
d) motor protein
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Explanation: Tropomodulin is a capping protein that caps the pointed ends of the actin filaments. The capping proteins regulate the length of actin filaments.
8. Which of the following has an opposing role as that of thymosin?
a) chymosin
b) vimentin
c) profilin
d) niacin
View Answer
Explanation: Profilin has the role of binding to G-actin and promoting the growth of actin filaments rather than inhibiting (like thymosin).
9. Which of the following can fragment actin filaments?
a) profilin
b) thymosin
c) cofilin
d) vimentin
View Answer
Explanation: Cofilin is a family of proteins that include ADF, depactin. These proteins can fragment actin filaments and can promote depolymerization at the pointed end.
10. Filamin is an example of ___________ proteins.
a) capping
b) depolymerization
c) motor
d) cross-linking
View Answer
Explanation: Filamin is a cross-linking protein; such proteins have the ability to alter three-dimensional organization of a population of actin filaments.
11. Cross-linking proteins villin and fimbrin are found in ___________
a) neurons
b) myoblasts
c) microvilli
d) flagella
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Explanation: Villin and fimbrin are globular cross-linking proteins that promote the bundling of actin filaments into parallel and tightly-knit arrays. Such arrays are found in microvilli of epithelial cells.
12. The protein responsible for muscular dystrophy, dystrophin, is a __________ protein.
a) cross-linking
b) membrane-binding
c) tethering
d) severing
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Explanation: Dystrophin is a cylindrical shaped protein made up of about 3700 amino acid residues and is present in the muscles. It attaches the muscle fibres to the surrounding extracellular matrix thereby acting as a membrane binding protein.
13. An organism in which cell motility takes place solely as a result of actin polymerization is ____________________
a) E. coli
b) Corynebacterium
c) Listeria monocytogenes
d) Clostridium botulinum
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Explanation: In the bacterium Listeria monocytogenes which infects the macrophages and causes food poisoning, cell motility is facilitated solely by the polymerization of actin.
14. ActA, a surface protein activates the ______________
a) Arp2/3 complex
b) Sar1
c) Arf1
d) EcoR1
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Explanation: ActA is a surface protein found on one side of the bacterium Listeria monocytogenes, when inside the host cell it activates the Arp 2/3 complex and other proteins that work together to direct the process of actin polymerization.
15. Lamellipodium is a protrusion of ________________
a) actin filaments
b) fibroblasts
c) myoblasts
d) neurons
View Answer
Explanation: Lamellipodium is a cellular extension that occurs in motile cells such as fibroblasts and keratinocytes. These projections are caused by actin filaments and are seen on the edges of the cells.
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