This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cytoskeleton – Microfilaments”.
1. Microfilaments are mostly involved in _______________ processes.
Explanation: Microfilaments are skeletal filaments involved in processes involving cellular motility; such as movement of vesicles, phagocytosis and cytokinesis.
2. For cellular transport, plant cells rely on microfilaments.
Explanation: Unlike animal cells, plant cells rely primarily on microfilaments for long-distance transport of cytoplasmic organelles and vesicles.
3. Microfilaments are composed of globular subunits of _____________
Explanation: Microfilaments are composed of globular subunits of the protein actin. The actin monomers polymerize to form flexible helical filaments, in the presence of ATP.
4. The identification of actin filaments in a cell can be done by using the protein ____________
Explanation: Irrespective of the cell type and the role played in it by the microfilaments, all the actin filaments interact in a highly specific manner with the protein myosin. It is therefore used for the identification of microfilaments.
5. After incorporation into growing actin filaments, the associated ATP is _____________
Explanation: Actin units are added to the growing microfilament chain by the use of ATP. Each Actin subunit binds an ATP molecule. This ATP molecule is hydrolysed to ADP while the Actin unit is attached to the chain.
6. The faster growing end of the microfilament is the plus-end.
Explanation: Plus-end is the faster growing end of the actin filaments and incorporates actin monomers at a rate 10 times that of the other (minus) end.
7. The phenomenon of “treadmilling” is observed in microfilaments under the __________ state.
d) thermodynamically favorable
Explanation: Under the steady when the concentration of ATP and actin monomers is apt, the relative position of actin monomers in the filament keeps on changing because of the addition of the former on the positive-end and their removal on the minus-end. This phenomenon is called “treadmilling”.
8. The drug cytochalasin blocks the _____________
c) Plus-end of microfilaments
d) Minus-end of microfilaments
Explanation: The drug cytochalasin is obtained from a mold. It blocks the plus-ends of microfilaments (actin filaments) and causes depolymerization at the minus-end.
9. Latrunculin blocks the ____________
a) plus-end of microfilaments
b) minus-end of microfilaments
c) actin monomers
d) actin filaments
Explanation: Latrunculin is a toxin produced by certain sponges that blocks free actin monomers and prevents their incorporation into the polymer.
10. Which type of myosins move toward the minus-end of a microfilament?
a) myosin I
b) myosin II
c) myosin IV
d) myosin VI
Explanation: The proteins myosins work as motors in conjunction with the actin filaments. All myosins move towards the positive end of the actin filaments, except myosin VI which moves toward the minus end.
11. The head of the myosin binds the ___________
c) Actin filament
Explanation: The head of the myosin binds to the actin filament and its tail binds and hydrolyzes the ATP, to drive the myosin motor. The head domains of various myosins are similar whereas the tails are highly divergent.
12. Type II myosins are found primarily in __________
a) plant cells
b) muscle cells
c) nerve cells
d) liver hepatocytes
Explanation: The conventional myosins, type II are found in the muscle cells. This group of myosins are the best understood.
12. Myosins VIII and _____ are present only in plant cells.
Explanation: The myosin superfamilies are divided into two types, conventional and unconventional. Type VIII and XI belong to the latter type and are found only in the plant cells.
13. Myosin II filaments display a transient construction in ______________
a) nonmuscle cells
b) muscle cells
c) actin filaments
d) tubulin filaments
Explanation: Myosin II filaments are highly stable in the contractile apparatus of skeletal muscle cells. However in nonmuscle cells they often exhibit transient construction, assembling when required and disassembling after action.
14. Myosin I was discovered in the year _________
Explanation: Myosin I was discovered in 1973 by Thomas Pollard and Edward Korn of the National Institutes of Health. The protein was extracted from the protist Acanthamoeba.
15. Melanosomes are transferred into the developing hair by myosin ____
Explanation: Pigment granules, called melanosomes are transferred to the hair follicles after which they incorporate into the developing hair, by myosin V isoforms called Va.
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