Exam 17: Cytoskeleton

Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure 17-37.The three panels are images taken at 1-second intervals.In this figure, three microtubules have been numbered to make it easy to identify them.Which of the following statements about this assay is FALSE? Figure 17-37

Rank the following cytoskeletal filaments from smallest to largest in diameter (1 = smallest in diameter, 4 = largest) _____ intermediate filaments _____ microtubules _____ actin filament _____ myofibril

For both actin and microtubule polymerization, nucleotide hydrolysis is important for

Place the following in order of size, from the smallest to the largest. A)protofilament B)microtubule C)α-tubulin D)tubulin dimer E)mitotic spindle

Which of the following statements about organellar movement in the cell is FALSE?

In the three cell outlines in Figure 17-62, indicate the arrangement of the microtubules, showing clearly their free and attached ends.On each figure, indicate the plus end for one of the microtubules. (A) INTERPHASE CELL (C) CILLATED CFLL. (B) DNVDING CELL Figure 17-19

Consider the mechanism by which actin and tubulin polymerize.Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules?

Figure 17-38 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled. Figure 17-38 Which of the following statements is TRUE about muscle contraction?

Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure.Figure 17-6 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 IFαd.If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome? Figure 17-6

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. desmosome lamin synapse keratin neurofilament vimentin kinase plectin Intermediate filaments are found mainly in cells that are subject to mechanical stress.Gene mutations that disrupt intermediate filaments cause some rare human genetic 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, which code for 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.Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear __________.

Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure 17-20.Notice that the two types of cargo are traveling in opposite directions.Which of the following statements is likely to be FALSE? Figure 17-20

Which of the following statements about microtubules is TRUE?

Cytochalasin is a drug that caps actin filament plus ends, thus preventing actin polymerization.Phalloidin is a drug that binds to and stabilizes actin filaments, preventing actin depolymerization.Even though these drugs have opposite effects on actin polymerization, the addition of either of these drugs instantaneously freezes the cell movements that depends on actin filaments.Explain why drugs that have opposite effects on actin filaments can have a similar effect on cell movements.

All intermediate filaments are of similar diameter because

Which of the following statements about actin is FALSE?

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 the nuclear lamina from its individual subunits in vitro.Which of the following additions do you predict would be most likely to enhance the assembly of the nuclear lamina?

Which of the following structures shorten during muscle contraction?

Which of the following statements is FALSE?

Do you agree or disagree with the following statement? Explain your answer. When skeletal muscle receives a signal from the nervous system to contract, the signal from the motor neuron triggers the opening of a voltage-sensitive Ca²⁺ channel in the muscle cells' plasma membrane, allowing Ca²⁺ to flow into the cell.