Cell Bio Week 9
Quiz by Haniya Hopson
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- Q1
Why do you suppose it is much easier to add tubulin dimers to existing microtubules than to start a new microtubule from scratch?
Tubulins slide along a microtubule till reaching the end.
Individual tubulin dimers do not bind to one another.
It is easier for tubulin to find the end of a microtubule.
More contacts are available at the end of a microtubule.
120s - Q2
What is the term for the property of sudden conversion of a microtubule from growth to shrinkage, and vice versa? Choose one:
Rescue
Catastrophe
Treadmilling
Dynamic instability
120s - Q3
Anticancer drugs like paclitaxel and colchicine are used to kill certain kinds of tumor cells because these drugs are not toxic to rapidly dividing normal cells.
True
False
120s - Q4
In the presence of centrosomes, the critical concentration for microtubule growth is 4 μM. In a classic analysis of microtubule dynamics, microtubules were grown from centrosomes at a tubulin concentration of 25 μM. The centrosomes were then diluted into lower concentrations of tubulin, and the number and length of microtubules were plotted as a function of time (see the figure).This experiment revealed that when diluted to 7.5 μM tubulin, the number of microtubules attached to each centrosome decreased with time, and the average length of the remaining microtubules increased. At neither 15 μM nor 5 μM did both these changes occur.Which one of the following interpretations best accounts for the decrease in microtubule number and the increase in microtubule length upon dilution to 7.5 μM tubulin?
Dilution releases some microtubules from the centrosome, allowing them to rapidly depolymerize from their minus ends.
After dilution, the tubulin concentration is below the critical concentration for plus-end growth, so some microtubules shrink.
After dilution, some microtubules continue to hydrolyze GTP, which allows them to continue to grow from their plus ends.
At lower tubulin levels, microtubules with a GTP cap continue to grow, but those with a GDP cap rapidly depolymerize.
120s - Q5
GTP hydrolysis and whether GTP or GDP is bound to tubulin is an important mechanism to control the dynamic instability of microtubules. Certain aspects of dynamic instability can be viewed using GFP-EB1. Which process(es) is it useful for visualizing and why?
Shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules
Growing microtubules, because EB1 binds to the GTP-tubulin cap on microtubules
Growing and shrinking microtubules, because EB1 binds to the GDP-tubulin cap on microtubules
Growing and shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules
120s - Q6
How would the microtubule dynamics change after adding a non-hydrolyzable analog of GTP to the cells?
Microtubules would shrink.
Microtubules would grow longer.
Microtubule dynamics would not change.
Dynamic instability would increase as microtubules rapidly switch between growing and shrinking.
120s - Q7
When cells enter mitosis, their existing array of cytoplasmic microtubules must be rapidly broken down and replaced with the mitotic spindle, which pulls the chromosomes into the daughter cells. The enzyme katanin, named after Japanese samurai swords, is activated during the onset of mitosis. Katanin extracts tubulin subunits from the wall of cellular microtubules, weakening its structure and promoting breakage. What do you suppose is the usual fate of the microtubule fragments created by katanin?
The fragments serve as seeds for growth from their plus ends.
The fragments are rapidly stabilized by end-binding proteins.
The fragments depolymerize because they contain GDP-tubulin.
The fragments are joined to rapidly form mitotic microtubules.
120s - Q8
Mice that are homozygous for a knockout of the gene for the kinesin motor protein KIF1B die at birth. Heterozygous knockouts (one copy deleted) survive but suffer from a progressive muscle weakness similar to human neuropathies. Humans with Charcot–Marie–Tooth disease type 2A have a mutation in one copy of the gene for KIF1B that prevents the protein from binding to ATP. The heterozygous mice and the human patients have very similar progressive neuropathies.How do you suppose that the loss of one copy of a gene for a kinesin motor can have such profound effects on nerve function?
The mouse knockout is recessive; one normal gene makes enough kinesin.
The normal gene produces twice as much kinesin but can’t keep doing so.
Half the usual amount of kinesin cannot keep up with the needs of nerves.
The human gene with a point mutation makes slow moving kinesin motors.
120s - Q9
Fish melanocytes provide a dramatic example of the ability of a cell to regulate the activity of motor proteins to cause a change in the position on its membrane-enclosed organelles. These giant cells contain large membrane-enclosed organelles, termed pigment granules, that can aggregate in the center of the cell or disperse by moving along an extensive network of microtubules that are anchored at the centrosome (see the figure).Which one of the following statements correctly describes the role of motor proteins in the movements of the pigment granules?
Dyneins and kinesins both function during dispersal of granules.
Dynein motors are required to disperse the pigment granules.
Kinesin motors are required to aggregate the pigment granules.
Myosin motors are required to disperse the pigment granules.
120s - Q10
Which of the following defects have been found in individuals with one of a set of disorders known as ciliopathies?
I Defects in intraflagellar transport (IFT)
II Defects in the primary cilium
III Defects in the basal body
IV Defects in myosin motor proteins
I, II, and III
I and IV
II, III, and IV
I, II, and IV
120s - Q11
Communication among cytoskeletal elements coordinates whole-cell polarization and locomotion.
False
True
120s - Q12
What is the term for the collection of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell its shape and the capacity for directed movement?
Intermediate filaments
Cytoskeleton
Actin filaments
Microtubules
120s - Q13
Which of the paired electron micrographs and fluorescence micrographs in the figure correspond, respectively, to actin filaments, microtubules, and intermediate filaments?
Actin filaments (C); microtubules (B); intermediate filaments (A).
Actin filaments (B); microtubules (C); intermediate filaments (A).
Actin filaments (C); microtubules (A); intermediate filaments (B).
Actin filaments (B); microtubules (A); intermediate filaments (C).
Actin filaments (A); microtubules (C); intermediate filaments (B)
Actin filaments (A); microtubules (B); intermediate filaments (C).
120s - Q14
Actin filaments are responsible for large-scale cellular polarity, enabling cells to tell the difference between top and bottom, or front and back.
False
True
30s - Q15
What is the term for the linear chain of protein subunits joined end-to-end, which associates laterally with other such chains to form a microtubule?
Intermediate filament
Actin filament
Protofilament
Stress fiber
45s
