CHAPTER 17 CYTOSKELETON 2009 Garland Science Publishing 17 1 Identify the cytoskeletal structures depicted in the epithelial cells shown in Figure Q17 1 Figure Q17 1 17 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 ATP B includes keratin and neurofilaments C important for formation of the contractile ring during cytokinesis D supports and strengthens the nuclear envelope E their stability involves a GTP cap F used in the eucaryotic flagellum G a component of the mitotic spindle H can be connected through desmosomes I directly involved in muscle contraction J abundant in filopodia 17 4 Which of the following statements about the cytoskeleton is true a All eucaryotic cells have actin microtubules and intermediate filaments in their 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 end that 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 myofibril Intermediate Filaments 17 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 m 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 helical region is twice as long as that of a normal intermediate filament by duplicating the normal helical region while keeping a globular head at the N terminus and a globular tail at the C terminus you call this subunit IF d If you were to assemble intermediate filaments using IF2 d as the subunit which of the following predictions below describes the most likely outcome Figure Q17 7 a b c d 17 8 Filaments assembled using IF d will interact with different cytoskeletal components Filaments assembled using IF d will form dimers that are twice as long as dimers assembled from normal intermediate filaments Sixteen tetramers assembled from IF d will be needed for a ropelike structure to form Dimers of IF d will form by interactions with the N terminal globular head and the C terminal globular tail 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 of people 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 nervous system 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 keratin kinase 17 9 lamin neurofilament plectin synapse vimentin Match the type of intermediate filament with its appropriate location lamins neurofilaments vimentins keratins A nerve cells B epithelia C nucleus D connective tissue 17 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 enhance the 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 inhibitors Microtubules 17 13 Place the following in order of size from the smallest to the largest A protofilament B microtubule C tubulin D tubulin dimer E mitotic spindle 17 14 In the three cell outlines in Figure Q17 14 indicate the arrangement of the microtubules showing clearly their free and attached ends On each figure indicate the plus end and the minus end for one of the microtubules Figure Q17 14 17 15 Which of the following statements about