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CYTOSKELETON  2009 Garland Science Publishing 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! "he cytoskeleton is made up of three types of protein filament. (b) "he bacterial cytoskeleton is important for cell division and D&' segregation. (c! (rotein monomers that are held together with co$alent bonds form cytoskeletal filaments. (d) "he cytoskeleton of a cell can change in response to the environment. 17-3 Indicate which of the three ma)or classes of cytoskeletal elements each statement below refers to. '. monomer that binds A"( B. includes keratin and neurofilaments C. important for formation of the contractile ring during cytokinesis %. supports and strengthens the nuclear en$elope ,. their stability in$ol$es a G"( cap F. used in the eucaryotic flagellum -. a component of the mitotic spindle /. can be connected through desmosomes I. directly in$ol$ed in muscle contraction 0. abundant in filopodia 17-4 Which of the following statements about the cytoskeleton is true? (a! 'll eucaryotic cells ha$e actin, microtubules1 and intermediate filaments in their cytoplasm. (b) "he cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. (c! "he three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. (d) 'ctin filaments and microtubules ha$e an inherent polarity1 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 diameter1 4 = largest! ______ intermediate filaments ______ microtubules ______ actin filament ______ myofibril Intermediate Filaments 17-6 Which of the statements below about intermediate filaments is false? (a! "hey can stay intact in cells treated with concentrated salt solutions. (b) "hey can be found in the cytoplasm and the nucleus. (c! "hey can be anchored to the plasma membrane at cell-cell junction. (d) ,ach 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 the normal α-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 IF<:d as the subunit, which of the following predictions below describes the most likely outcome? Figure Q17-7 (a! Filaments assembled using IF:d will interact with different cytoskeletal components. (b) Filaments assembled using IF:d will form dimers that are twice as long as dimers assembled from normal intermediate filaments. (c! >ixteen tetramers assembled from IF:d will be needed for a ropelike structure to form. (d) %imers of IF:d 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 #laments cause some rare human diseases. For e?ample1 the skin of people with epidermolysis bullosa simple? is very susceptible to mechanical injury; people with this disorder ha$e mutations in their __________________ genes, the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called __________________s. The main #laments found in muscle cells belong to the __________________ family; people with disruptions in these intermediate filaments can ha$e muscular dystrophy. In the ner$ous system1 __________________s help strengthen the extremely long extensions often present in ner$e cell a?ons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for __________________, an important protein for cross-linking intermediate filaments1 ha$e a disease that combines symptoms of epidermolysis bullosa simple?1 muscular dystrophy1 and neurodegeneration. desmosome lamin synapse keratin neurofilament vimentin kinase plectin 17-9 @atch the type of intermediate filament with its appropriate location. lamins _________ '. ner$e cells neurofilaments _________ B. epithelia vimentins _________ C. nucleus keratins _________ %. connecti$e tissue 17-10 Aeratins1 neurofilaments1 and vimentins are all categories of intermediate #laments. Which of the following properties below is not true of these types of intermediate filaments? (a! "hey strengthen cells against mechanical stress. (b) %imers associate by nonco$alent bonding to form a tetramer. (c! "hey are found in the cytoplasm. (d) (hosphorylation causes disassembly during e$ery mitotic cycle. 17-11 (hosphorylation of nuclear lamins regulates their assembly and disassembly during mitosis. You add a drug to cells undergoing mitosis that inhibits the activity of an enzyme that dephosphorylates nuclear lamins. What do you predict will happen to these cells? Why? 17-12 9ou are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly puri#ed nuclear lamina subunits to which you will add back puri#ed cellular components to dri$e nuclear lamina assembly. Before you start doing experiments1 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 A"( (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 (lace the following in order of siBe, from the smallest to the largest. '. protofilament B. microtubule C. :-tubulin %. tubulin dimer ,. mitotic spindle 17-14 In the three cell outlines in Figure Q17-14, indicate the arrangement of the microtubules1 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 microtubules is true? (a! @otor proteins mo$e in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) "he centromere nucleates the microtubules of the mitotic spindle. (c! Because microtubules are subject to dynamic instability1 they are used only for transient structures in a cell. (d) '"( hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule. 17-16 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once. @icrotubules are formed from the tubulin heterodimer1 which is composed of the nucleotide-binding __________________ protein and the __________________ protein. Tubulin dimers are stacked together into protofilaments; __________________ parallel protofilaments form the tubelike structure of a microtubule. __________________ rings are important for microtubule nucleation and are found in the __________________ , which is usually found near the cellDs nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will ha$e a __________________ cap that helps pre$ent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a __________________ and in$ol$e a “__________________ plus two” array of microtubules. The motor protein __________________ generates the bending motion in cilia; the lack of this protein can cause KartagenerDs syndrome in humans. basal body G-tubulin '"( myosin H"( nine dynein thirteen I-tubulin -"( centrosome four twenty-one J-tubulin vimentin :-tubulin kinesin two 17-17 "he hydrolysis of G"( to G%( carried out by tubulin molecules ________________. (a! provides the energy needed for tubulin to polymeriBe (b) occurs because the pool of free G%( has run out (c! tips the balance in fa$or of microtubule assembly (d) allows the behavior of microtubules called dynamic instability 17-18 "he microtubules in a cell form a structural framework that can ha$e all the following functions except which of the following? (a! holding internal organelles such as the Golgi apparatus in particular positions in the cell (b) creating long thin cytoplasmic extensions that protrude from one side of the cell (c! strengthening the plasma membrane (d) moving materials from one place to another inside a cell 17-19 9ou are curious about the dynamic instability of microtubules and decide to join a lab that works on microtubule polymeriBation. The people in the lab help you .
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