Engineering Questions with Answers - Multiple Choice Questions
MCQs on Cytoskeleton – Microtubules
1 - Question
Where in a eukaryotic cell, can a microtubule NOT be found?
a) flagella
b) mitotic spindle
c) nucleus
d) cilia
View Answer
Answer: c
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 - Question
Which type of macromolecules make up the wall of microtubules?
a) globular proteins
b) glycoproteins
c) deoxyribonucleic acids
d) carbohydrates
View Answer
Answer: a
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 - Question
How many protofilaments are present in a single mammalian microtubule?
a) 5
b) 13
c) 20
d) 26
View Answer
Answer: b
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 - Question
All the protofilaments of a microtubule have the same _____________
a) polarity
b) pH
c) fluorescence
d) torque
View Answer
Answer: a
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 - Question
Alpha-tubulin subunits terminate the plus end of the microtubule.
a) True
b) False
View Answer
Answer: b
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 - Question
The microtubule-binding activity of MAPs is controlled by ______________
a) phosphorylation
b) oxidation
c) reduction
d) hydrolysis
View Answer
Answer: a
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 - Question
Neurofibrillary tangles, found in the brain cells of persons with neurodegenerative disorders consists of _______________
a) intermediate filaments
b) microtubule-associated proteins
c) microtubules
d) phospholipids
View Answer
Answer: b
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 - Question
. The drug colchicine promotes microtubule _____________
a) disassembly
b) assembly
c) acidification
d) condensation
View Answer
Answer: a
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 - Question
Movement of materials in an axon are mediated through ________________ that serve as cytoskeletal tracks.
a) microtubules
b) actin filaments
c) microfilaments
d) intermediate filaments
View Answer
Answer: a
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 - Question
. Which motor protein superfamily does not move along the microtubules?
a) Dynein
b) Kinesin
c) Myosin
d) Calmodulin
View Answer
Answer: c
Explanation: Motor proteins are divided into three superfamilies: dyneins, myosins and kinesins. Dyneins and kinesins move along microtubules, and myosins move along microfilaments.
11 - Question
Smallest microtubular motor proteins are __________________
a) dyeneins
b) niacin
c) thiamine
d) kinesin
View Answer
Answer: d
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 - Question
Kinesins are plus end-directed microtubular proteins.
a) True
b) False
View Answer
Answer: a
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 - Question
In an axon, microtubules are oriented with their __________________ facing the cell body.
a) plus end
b) minus end
c) vertical axis
d) periphery
View Answer
Answer: b
Explanation: In an axon, all microtubules are oriented with their plus ends facing the synaptic terminals and minus ends facing the cell body.
14 - Question
Which protein moves towards the minus end of the microtubule track?
a) Nac
b) ARF
c) Sar1
d) Ncd
View Answer
Answer: d
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 - Question
Which of the following family of kinesins is incapable of movement along the microtubules?
a) kinesin-1
b) kinesin-3
c) kinesin-13
d) kinesin-14
View Answer
Answer: c
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.