Mastering - Chapter 13 cell biology
EB1
binds to microtubule plus ends
MAPs
stabilizes and organizes microtubules
plectin
crosslinks microtubules to intermediate filaments
phosphoinositides
binds to profilin and CapZ
filamin
connects crisscrossing actin filaments into 3D networks
Provide a brief justification for the following false answer:An algal cell contains neither tubulin nor actin.
Algae are eukaryotes and therefore possess the same kinds of cytoskeletal components as other eukaryotic cells.
It is now possible, using nanoengineering techniques, to attach magnetic beads to the surface of large cells to measure how mechanically stiff they are. It is also known that acrylamide, which is polymerized to make gels for protein electrophoresis, is very toxic. One effect of acrylamide is to depolymerize intermediate filaments, such as keratin: What effect would you predict acrylamide treatment would have on the mechanical rigidity of a keratinocyte (skin cell)? Explain your answer
Disrupting intermediate filaments will result in cells that are more susceptible to mechanical forces. In the case of the keratinocytes, disrupting keratin, a key IFIF in these cells, would result in very fragile cells. Less force would need to be applied using the magnetic beads to damage them or change their shape.
All microtubules within animal cells have their minus ends anchored at the centrosome.
False
An algal cell contains neither tubulin nor actin.
False
The energy required for tubulin and actin polymerization is provided by hydrolysis of a nucleoside triphosphate.
False
The minus end of microtubules and microfilaments is so named because subunits are lost and never added there.
False
What hypothesis was being tested with the Δformin strain?
Formin is required for the signal transduction pathway leading to shmoo formation.
A model helps scientists form testable hypotheses. What hypothesis was being tested with the ΔFus3 strain?
Fus3 is required for the signal transduction pathway leading to shmoo formation.
What causes catastrophe of the microtubule in vitro?
GTP hydrolysis
What is the role of GTP in microtubule polymerization?
GTP stabilizes the tip of the microtubule, allowing more monomers to be added.
Provide a brief justification for the following false answer:The energy required for tubulin and actin polymerization is provided by hydrolysis of a nucleoside triphosphate.
Hydrolysis of the ATP bound to actin and the GTP bound to tubulin usually occurs during monomer polymerization, but the polymerization process still occurs even if the ATP or GTP is replaced by a nonhydrolyzable analogue.
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements.: Most likely to remain when cells are treated with solutions of nonionic detergents or solutions of high ionic strength
IF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements.: More important for cytokinesis than for chromosome movements in animal cells.
MF
Indicate whether each of the following descriptions is true of microtubules(MT), microfilaments(MF), intermediate filaments(IF), or none of these(N). More than one response may be appropriate for some statements.: Involved in muscle contraction
MF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements.: Involved in the movement of cilia and flagella
MT
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements.: More important for chromosome movements than for cytokinesis
MT
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements: The fundamental repeating subunit is a dimer.
MT and IF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements: Play well-documented roles in cell movement.
MT and MF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements: Their subunits can bind and catalyze hydrolysis of phosphonucleotides.
MT and MF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements: Can be detected by immunofluorescence microscopy.
MT, MF, and IF
Indicate whether each of the following descriptions is true of microtubules (MT)(MT), microfilaments (MF)(MF), intermediate filaments (IF)(IF), or none of these (N)(N). More than one response may be appropriate for some statements: Structurally similar proteins are found in bacterial cells.
MT, MF, and IF
As long as actin monomers continue to be added to the plus end of a microfilament, the \(\rm MF\) will continue to elongate.
Maybe
Provide a brief justification for the following false answer:All microtubules within animal cells have their minus ends anchored at the centrosome.
Most do, but not all. In addition, in ciliated or flagellated cells, the minus ends of microtubules can be anchored at the basal body, which also serves as a microtubule-organizing center.
What do you predict would happen if the yeast had a mutation that prevented the G protein from binding GTP?
No shmoo would form in response to mating factor. Explanation: If the G protein could not bind GTP, it would not become activated, and so it would not start the phosphorylation cascade.
Small vesicles containing pigment inside of pigmented fish epidermal cells aggregate or disperse in response to treatment with certain chemicals. When nocodazole is added to cells in which the pigment granules have been induced to aggregate, the granules cannot disperse again.
Pigment granule dispersal is a microtubule-dependent process.
Wild Type: What color is the cell wall? What type of growth is the cell undergoing? Has a shmoo formed? Are the results consistent with the hypothesis? Are the results consistent with the working model of shmoo formation?
Red and green Asymmetrical Yes Yes Yes
Suppose you have determined the overall critical concentration for a sample of purified tubulin. Then you add a preparation of centrosomes (microtubule-organizing centers), which nucleate microtubules so that the minus end is bound to the centrosome and stabilized against disassembly. When you again determine the overall critical concentration, you find it is different. Explain why the overall critical concentration would change: The overall critical concentration should be _______ when tubulin polymerizes in the presence of the centrosome preparation.
Reduced
How would the drug taxol affect the in vitro dynamic instability and treadmilling experiments?
Taxol would stabilize the microtubules in both experiments, leading to polymerization without catastrophe.
When an animal cell is treated with colchicine, its microtubules depolymerize and virtually disappear. If the colchicine is then washed away, the MTs appear again, beginning at the centrosome and elongating outward at about the rate (1μm/min)(1μm/min) at which tubulin polymerizes in vitro.
The centrosome serves as a microtubule-organizing center in vivo, and all of the microtubules radiating from the centrosome apparently have the same polarity.
Extracts from nondividing frog eggs in the G2 phase of the cell cycle were found to contain structures that could induce the polymerization of tubulin into microtubules in vitro. When examined by immunostaining, these structures were shown to contain γγ-tubulin.
The extracts appear to contain structures that are functionally equivalent to centrosomes (as evidenced by the presence of γγ-tubulin), which nucleate micro-tubule growth.
What would happen in the treadmilling experiment if a non-hydrolyzable analogue of GTP were used?
The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end.
Latrunculin A treatment would block intracellular movements of Listeria.
True
Microtubules, microfilaments, and intermediate filaments all exist in a typical eukaryotic cell in dynamic equilibrium with a pool of subunit proteins.
True
Fus3 kinase and formin proteins are generally distributed evenly throughout a yeast cell. Based on the model in the diagram, why does the shmoo projection emerge on the same side of the cell that bound the mating factor?
The only formin molecules that get phosphorylated and thus activated are those near the G protein-coupled receptor that binds mating factor. Explanation: Because the mating factor is diffusing from the direction of the other mating-type yeast, it is the G protein-coupled receptors on that side of the cell that bind mating factor, become activated, and start the phosphorylation cascade that activates Fus3, which activates formin, which leads to localized shmoo formation.
The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end.
The plus end has a lower critical concentration for tubulin heterodimers.
Provide a brief justification for the following false answer:The minus end of microtubules and microfilaments is so named because subunits are lost and never added there.
The rate of loss is greater than the rate of addition at the minus end over time. There is no absolute absence of addition at the minus end.
Provide a brief justification why the following answer can be either true or false:As long as actin monomers continue to be added to the plus end of a microfilament, the MF will continue to elongate.
The statement is true if the monomer concentration is above the overall critical concentration but false otherwise.
First, the existing cell walls of each strain were stained with a green fluorescent dye. These green-stained cells were then exposed to mating factor and then stained with a red fluorescent dye that only labels new cell wall growth. Growth of the cell on all sides (symmetric growth) is indicated by a uniform yellow color, resulting from merged green and red stains. This occurs normally in wild-type cells that have not been exposed to mating factor. The image below shows the fluorescence pattern in wild-type yeast cells that have been exposed to mating factor. Note the asymmetric growth. One of their hypotheses was that Fus3 kinase is required for the signal transduction pathway leading to shmoo formation. If this hypothesis is correct, what result should be observed in the ΔFus3 strain?
The ΔFus3 strain should not form shmoos, and the cells should not have a red zone in their walls.
One of their hypotheses was that formin is required for the signal transduction pathway leading to shmoo formation. If this hypothesis is correct, what result should be observed in the Δformin strain?
The Δformin strain should not form shmoos, and the cells should not have a red zone in their walls.
All of the protein subunits of intermediate filaments are encoded by genes in the same gene family
True
_______________ family proteins polymerization is very fast.
With Arp2/3 and WASP family proteins polymerization is very fast.
______________ polymerization increases, but not as much as ______________ family proteins.
With Arp2/3 polymerization increases, but not as much as with Arp2/3 and WASP family proteins.
________________ family proteins polymerization is very slow.
Without Arp2/3 or WASP family proteins polymerization is very slow.
ΔFus3: What color is the cell wall? What type of growth is the cell undergoing? Has a shmoo formed? Are the results consistent with the hypothesis? Are the results consistent with the working model of shmoo formation?
Yellow symmetrical No Yes Yes
ΔFormin: What color is the cell wall? What type of growth is the cell undergoing? Has a shmoo formed? Are the results consistent with the hypothesis? Are the results consistent with the working model of shmoo formation?
Yellow symmetrical No Yes Yes
treadmilling
assembly and disassembly on opposite ends of the same filament
Intermediate filaments: a) Intermediate filamentsare 7 nm in diameter. b) can be composed of the protein vimentin. c) are the only cytoskeletal filament responsible for animal cell shape. d) are abundant in plant cells. e) are 7 nm in diameter, are the only cytoskeletal filament responsible for animal cell shape, are abundant in plant cells, and can be composed of the protein vimentin.
b
Which of the following is not associated with the bundle of microfilaments supporting each microvillus in small intestine mucosal cells?: a) fimbrin b) fascin c) myosin I (one) d) villin e) All are associated with the microvillus microfilament bundle.
b
gelsolin
breaks and caps actin filaments
myosin subfragment 1 (S1)
decorates actin microfilaments
nucleation
formation of tubulin oligomers
lamin
forms scaffold underlying nuclear envelope
Which of the following proteins would be a good drug target for interfering with microfilament network breakdown?
gelsolin
Which phase of microtubule polymerization in vitro would be affected most by adding short microtubules to unpolymerized GTP-tubulin?
lag phase
axonemal microtubules
is in cilia and flagella
desmin
keeps muscle myofibrils in register
Arp2/3 complex
nucleates actin filament branches
Based on what you know about the molecular mechanism of action of cytochalasins, explain what happens to microfilaments within cells treated with the drug and why existing actin polymers eventually depolymerize: Cytochalasin D ______ of monomers at ______ of existing filaments. When the concentration of G-actin in the cytosol is ______ the critical concentration, the loss of monomers at ________ of existing filaments eventually results in their shortening. This occurs despite the pool of available G-actin in the cytosol.
prevents addition, plus ends, below, minus ends
CapZ
prevents assembly and disassembly at microfilament plus ends.
tropomodulin
prevents loss of subunits from filament minus end
In addition to testing shmoo formation in the two mutant strains of yeast, the scientists also tested shmoo formation in wild-type yeast.
to show normal shmoo formation under the experimental conditions
Suppose you have determined the overall critical concentration for a sample of purified tubulin. Then you add a preparation of centrosomes (microtubule-organizing centers), which nucleate microtubules so that the minus end is bound to the centrosome and stabilized against disassembly. When you again determine the overall critical concentration, you find it is different. Explain why the overall critical concentration would change: If the minus end cannot disassemble, the overall critical concentration should now be equivalent ______ critical concentration of the _______ end.
to the lower, plus
Which of the following is true about the structure of the microtubule wall?
α-β-tubulin heterodimers are arranged with the same orientation in each protofilament, and protofilaments are arranged with same polarity in the microtubule wall.
