Chapter 17 - Cytoskeleton Flashcards
Which is the toughest and most durable of the different types of cytoskeletal filaments?
- dynein
- actin filaments
- intermediate filaments
- myosin
- microtubules
Intermediate filaments
(Intermediate filaments are the toughest and most durable of the three types of cytoskeletal filaments and can even survive treatment with concentrated salt solutions and detergents.)
Intermediate filaments are found in what structure?
- nuclear lamina
- centrosomes
- mitotic spindle
- cell cortex
- cilia
Nuclear lamina
(Intermediate filaments, specifically lamin proteins, are found in the nuclear lamina. This cytoskeletal meshwork underlies and strengthens the nuclear envelope.)
Which term best describes the structure of intermediate filament monomers?
- tubelike
- springlike
- ropelike
- meshlike
Ropelike
(Intermediate filament monomers are best described as ropelike structures. Fibrous, intermediate filament proteins twist together to form these ropelike structures.)
Which of the following types of intermediate filaments are found in all animal cells?
- nuclear lamins
- keratin filaments
- vimentin and vimentin-related filaments
- neurofilaments
Nuclear lamins
Nuclear lamins are intermediate filaments that are found in the nuclei of all animal cells as well as plant cells.
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?
- growing and shrinking microtubules, because EB1 binds to the GDP-tubulin cap on microtubules
- 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 GTP-tubulin cap on microtubules
growing microtubules, because EB1 binds to the GTP-tubulin cap on microtubules
(GFP-EB1 binds the GTP-bound tubulin subunits in the microtubule, thereby labeling the growing microtubules.)
How would the animation of microtubule dynamics change after adding a non-hydrolyzable analog of GTP to the cells expressing GFP tubulin?
- Microtubule dynamics would not change.
- Dynamic instability would increase as microtubules rapidly switch between growing and shrinking.
- Microtubules would shrink.
- Microtubules would grow longer.
Microtubules would grow longer.
The microtubules would have permanent GTP caps and would continue to grow and not shrink.
Within this image, the _______ cargo is being transported by kinesin and the ______ cargo is being transported by dynein.
Red; Blue
(Within this image, the red cargo is being transported by kinesin. Kinesin uses the hydrolysis of ATP to migrate toward the plus end of a microtubule.
Correct. Within this image, the blue cargo is being transported by dynein. Dynein uses the hydrolysis of ATP to migrate toward the minus end of a microtubule.)
What does the cellular motility of sperm depend on?
- actin and myosin
- actin and kinesin
- microtubules and dynein
- microtubules and kinesin
Microtubules and dynein
(Flagella propel a sperm cell through fluid using a repetitive wavelike motion that is dependent on flagellar microtubules and the motor protein dynein.)
Which of the following cytoskeletal structures are the most common for providing tracks for guiding intracellular transport?
- kinesins
- dyneins
- intermediate filaments
- actin filaments
- microtubules
Microtubules
(Microtubules are cytoskeletal structures that provide tracks for guiding intracellular transport of vesicles, organelles, and other cell components in the cytosol.)
What do microtubules resemble?
- meshlike networks
- ropelike strands
- hollow tubes
- interlocking chains
Hollow tubes
Microtubules are composed of 13 parallel protofilaments that, bundled together, resemble a hollow tube.
Dynamic instability in microtubules stems from the intrinsic capacity of tubulin molecules to hydrolyze what?
- peptide bonds
- GTP
- ATP
- water
- tubulin dimers
GTP
(Dynamic instability in microtubules stems from the intrinsic capacity of tubulin molecules to hydrolyze GTP. β-tubulin hydrolyzes its bound GTP shortly after a dimer is added to a growing microtubule.)
Which of the following describes the structure of an actin filament?
- It is a structure with a long tail and two globular heads.
- It is a twisted chain of actin molecules.
- It is a hollow cylinder made of actin molecules.
It is a twisted chain of actin molecules.
(Each filament is a twisted chain of identical globular actin monomers, all of which “point” in the same direction along the axis of the chain.)
What is the name of the thin, sheetlike structures that a fibroblast regularly extends during cell crawling?
- phagosomes
- filopodia
- lamellipodia
- pseudopods
Lamellipodia
(The lamellipodia are the thin, sheetlike structures that a fibroblast regularly extends during cell crawling. These structures contain a dense meshwork of actin filaments.)
In what kind(s) of cells is myosin-I present?
- nerve cells only
- muscle cells only
- epithelial cells only
- all types of cells
All types of cells
(Myosin-I is present in all types of cells. A specialized form of myosin-II is present only in muscle cells, but myosin-I is needed in all cells.)
Which actin-binding proteins would be most involved in the assembly of the contractile ring?
- formins
- actin-related proteins
- γ-tubulin
- thymosins
Formins
(Formins aid in the assembly of unbranched actin filaments, including those in the contractile ring that pinches a dividing animal cell in two.)
An actin filament undergoing treadmilling at the leading edge of a lamellipodium can do what?
- remain the same size
- collapse and instantly disappear
- experience exponential growth
- add actin monomers to its minus end while losing them from its plus end
Remain the same size
(Treadmilling involves a simultaneous gain of monomers at the plus end of an actin filament and loss of monomers from the minus end; hence, actin filaments tend not to undergo drastic changes in length.)
Actin filaments can undergo ______ where actin monomers in the cytosol that carry ATP can join the filament.
treadmilling
Which does not contain both actin and myosin?
- the contractile ring that carries out cytokinesis
- the lamellipodium at the leading edge of a crawling cell
- a muscle cell sarcomere
- a contractile bundle in a nonmuscle cell
the lamellipodium at the leading edge of a crawling cell
The lamellipodia at the leading edge of a crawling cell contain actin but not myosin.
Inside a muscle fiber, what triggers sarcomeres to contract?
- a sudden rise in cytosolic Ca2+
- an increased availability of ATP
- a sudden rise in Ca2+ inside an organelle lumen
- a sudden rise in cytosolic Na+
- polarization of the muscle fiber plasma membrane
A sudden rise in cytosolic Ca2+
Inside a muscle fiber, a sudden rise in cytosolic Ca2+ activates proteins that initiate contraction of the sarcomeres.
Which organelle sequesters Ca2+ inside muscle fibers?
- lysosomes
- mitochondria
- Golgi apparatus
- sarcoplasmic reticulum
Sarcoplasmic reticulum
(The sarcoplasmic reticulum sequesters Ca2+ inside muscle fibers. This specialized region of the endoplasmic reticulum in muscle cells contains ATP-driven Ca2+ pumps that remove Ca2+ from the cytoplasm.)
When a muscle is stimulated to contract, what does Ca2+ bind to, and what effect does that have?
- tropomyosin, which moves the troponin that otherwise blocks the interaction of actin and myosin
- troponin, which moves the tropomyosin that otherwise blocks the interaction of actin and myosin
- myosin, allowing it to associate with actin
- actin, allowing it to associate with myosin
Troponin, which moves the tropomyosin that otherwise blocks the interaction of actin and myosin
(When a muscle is stimulated to contract, Ca2+ binds to troponin, which moves the tropomyosin that otherwise blocks the interaction of actin and myosin. In the absence of Ca2+, tropomyosin binds to actin monomers, preventing their interaction with myosin.)
Which of the following statements are consistent with the structure and function of intermediate filaments?
Choose one or more:
- Intermediate filaments are constructed of identical subunits found in all eukaryotic cells.
- Intermediate filaments can connect cells at cell–cell junctions called desmosomes.
- Intermediate filaments protect cells from mechanical stress because they have high tensile strength and resist stretching.
- Each filament is made of eight strands, and each strand is made from staggered tetramers linked end to end.
- Intermediate filaments can connect cells at cell–cell junctions called desmosomes.
- Intermediate filaments protect cells from mechanical stress because they have high tensile strength and resist stretching.
- Each filament is made of eight strands, and each strand is made from staggered tetramers linked end to end.
(Each filament with eight strands connects cells at desmosomes to protect from mechanical stress.)
Mutation of the muscle-specific intermediate filament desmin leads to the rare disease desmin-related myopathy. This disorder starts with weakness of the lower limbs when patients are in their 20s or 30s. As symptoms worsen, weakness in respiratory and cardiac muscles occurs, which can lead to serious problems including sudden cardiac arrest.
Which of the following mutations would disrupt desmin intermediate filament structure or function and could explain the symptoms of desmin-related myopathy? Choose all of the possible mutations.
Choose one or more:
- Alteration in the twist or coiling of the dimers, blocking formation of staggered tetramers.
- Disruption of the polarity of the final desmin strands.
- Alteration in head groups, so tetramers are unable to link end to end.
- Mutation such that formation of dimers is blocked.
- Alteration in the twist or coiling of the dimers, blocking formation of staggered tetramers.
- Alteration in head groups, so tetramers are unable to link end to end.
- Mutation such that formation of dimers is blocked.
(Intermediate filament function depends on their proper assembly. Assembly begins with monomers forming coiled-coil dimers. The dimers then associate to form a staggered tetramer. The tetramers form such that both ends of the tetramer are identical, so intermediate filaments do not have polarity. The staggered tetramers join end to end to make a long strand. Eight strands associate to make the final ropelike intermediate filament. Disruption of any of these stages of assembly would block proper filament assembly and function and could lead to desmin-related myopathy.)
Which statement about intermediate filaments is not true?
- They rupture under stress.
- They have the highest tensile strength of all the cytoskeletal filaments.
- Their disruption can lead to premature aging.
- They are wider than actin filaments.
- They lack polarity.
They rupture under stress.
(Intermediate filaments deform under stress, but they do not rupture. The tensile strength that maintains cell integrity, especially that of epithelial cells, is due to keratin—a strong intermediate filament polymer.)