CYTOSKELETONIntermediate FilamentsMicrotubulesActin FilamentsMuscle ContractionHow We Know: Pursuing Motor ProteinsCHAPTER 17CYTOSKELETON 2009 Garland Science Publishing17-1 Identify the cytoskeletal structures depicted in the epithelial cells shown in Figure Q17-1.Figure Q17-117-2 Which of the following statements about the cytoskeleton is false?(a) The cytoskeleton is made up of three types of protein filament.(b) The bacterial cytoskeleton is important for cell division and DNA segregation.(c) Protein monomers that are held together with covalent bonds form cytoskeletal filaments.(d) The cytoskeleton of a cell can change in response to the environment.17-3 Indicate which of the three major classes of cytoskeletal elements each statement below refers to.A. monomer that binds ATPB. includes keratin and neurofilamentsC. important for formation of the contractile ring during cytokinesisD. supports and strengthens the nuclear envelopeE. their stability involves a GTP capF. used in the eucaryotic flagellumG. a component of the mitotic spindleH. can be connected through desmosomesI. directly involved in muscle contractionJ. abundant in filopodia17-4 Which of the following statements about the cytoskeleton is true?(a) All eucaryotic cells have actin, microtubules, and intermediate filaments intheir cytoplasm.(b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell.(c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another.(d) Actin filaments and microtubules have an inherent polarity, with a plus endthat grows more quickly than the minus end.17-5 Rank the following cytoskeletal filaments from smallest to largest in diameter (1 =smallest in diameter, 4 = largest)______ intermediate filaments______ microtubules______ actin filament______ myofibrilIntermediate Filaments17-6 Which of the statements below about intermediate filaments is false?(a) They can stay intact in cells treated with concentrated salt solutions.(b) They can be found in the cytoplasm and the nucleus.(c) They can be anchored to the plasma membrane at cell-cell junction.(d) Each filament is about 10 μm in diameter.17-7 Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-7 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating thenormal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assembleintermediate filaments using IF2αd as the subunit, which of the following predictions below describes the most likely outcome?Figure Q17-7(a) Filaments assembled using IFαd will interact with different cytoskeletal components.(b) Filaments assembled using IFαd will form dimers that are twice as long asdimers assembled from normal intermediate filaments.(c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form.(d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.17-8 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Intermediate filaments are found mainly in cells that are subject to mechanical stress. Mutations in genes that disrupt intermediate filaments cause some rare human diseases. For example, the skin ofpeople with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their__________________ genes, the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called __________________s. The main filaments found in muscle cells belong to the __________________ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervoussystem, __________________s help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for __________________, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex,muscular dystrophy, and neurodegeneration.desmosome lamin synapsekeratin neurofilament vimentinkinase plectin17-9 Match the type of intermediate filament with its appropriate location.lamins _________ A. nerve cellsneurofilaments _________ B. epitheliavimentins _________ C. nucleuskeratins _________ D. connective tissue17-10 Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties below is not true of these types of intermediate filaments?(a) They strengthen cells against mechanical stress.(b) Dimers associate by noncovalent bonding to form a tetramer.(c) They are found in the cytoplasm.(d) Phosphorylation causes disassembly during every mitotic cycle.17-11 Phosphorylation of nuclear lamins regulates their assembly and disassembly during mitosis. You add a drug to cells undergoing mitosis that inhibits the activity of an enzyme that dephosphorylates nuclear lamins. What do you predict will happen to these cells? Why?17-12 You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhancethe assembly of the nuclear lamina?(a) addition of phosphatase inhibitors(b) addition of ATP(c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm(d) addition of protein kinase inhibitorsMicrotubules17-13 Place the following in order of size, from the smallest to the