This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cytoskeleton – Microtubules”.
1. Where in a eukaryotic cell, can a microtubule NOT be found?
b) mitotic spindle
Explanation: Microtubules are hollow, rigid and tubular structures found in all eukaryotic cells. They are associated with the mitotic spindle and the core of cilia and flagella.
2. Which type of macromolecules make up the wall of microtubules?
a) globular proteins
c) deoxyribonucleic acids
Explanation: The walls of microtubules are composed of globular proteins arranged in longitudinal rows, called ‘protofilaments’, aligned parallel with the long axis of microtubule.
3. How many protofilaments are present in a single mammalian microtubule?
Explanation: There are about 10-15 protofilaments typically found in an animal cell. Exclusively in mammals there are 13 protofilaments which wound up together to form a 24 nm wide cylindrical tubule.
4. All the protofilaments of a microtubule have the same _____________
Explanation: All protofilaments of a microtubule have the same polarity, with alpha-tubulin at one end and beta-tubulin at the other. The entire polymer of microfilament is polar in nature.
5. Alpha-tubulin subunits terminate the plus end of the microtubule.
Explanation: The plus-end of the microtubule is terminated by a row of beta-tubulin subunits and the opposite, minus-end of the microtubule is terminated by a row of alpha-tubulin subunits.
6. The microtubule-binding activity of MAPs is controlled by ______________
Explanation: Microtubule-associated proteins (MAPs) increase the stability and promote the assembly of microtubules. Their binding activity is controlled by addition and removal of phosphate groups from particular amino acid residues.
7. Neurofibrillary tangles, found in the brain cells of persons with neurodegenerative disorders consists of _______________
a) intermediate filaments
b) microtubule-associated proteins
Explanation: Neurofibrillary tangles found in the brain cells of neurodegenerative diseases’ patients consists of tangled filaments of excessively phosphorylated ‘tau’ molecules. Tau molecules are a type of MAPs (microtubule-associated proteins).
8. The drug colchicine promotes microtubule _____________
Explanation: Drugs like nocodazole and colchicine promote the disassembly of microtubules. As a result of this disassembly, the Golgi complex originally located near the nucleus (center) is dispersed into peripheral region.
9. Movement of materials in an axon are mediated through ________________ that serve as cytoskeletal tracks.
b) actin filaments
d) intermediate filaments
Explanation: The movement of motor proteins towards or away from the cell body is mediated by the microtubules. The motor proteins generate forces within a cell that are essential for movement of materials across the cell.
10. Which motor protein superfamily does not move along the microtubules?
Explanation: Motor proteins are divided into three superfamilies: dyneins, myosins and kinesins. Dyneins and kinesins move along microtubules, and myosins move along microfilaments.
11. Smallest microtubular motor proteins are __________________
Explanation: Kinesins are the smallest motor proteins that use microtubules as their tracks. These were discovered in 1985 from the cytoplasm of squid giant axons. Kinesin is a tetramer consisting of two light and two heavy chains.
12. Kinesins are plus end-directed microtubular proteins.
Explanation: Kinesins are plus end-directed microtubular motor proteins. Plus end of a microtubule is where the tubulin molecules attach and detach, and growth or shrinkage takes place.
13. In an axon, microtubules are oriented with their __________________ facing the cell body.
a) plus end
b) minus end
c) vertical axis
Explanation: In an axon, all microtubules are oriented with their plus ends facing the synaptic terminals and minus ends facing the cell body.
14. Which protein moves towards the minus end of the microtubule track?
Explanation: Ncd is a protein of Drosophila that belongs to the family of kinesin-14 proteins. These proteins move in the opposite direction (compared to other kinesins), that is, towards the minus of the microtubules.
15. Which of the following family of kinesins is incapable of movement along the microtubules?
Explanation: Kinesin-13 represents a small family of kinesin-like proteins that are incapable of movement along the microtubules. These bind to either end of the microtubule and bring about its depolymerization.
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