Practice Questions ECM and Nucleus (T or F) Connexons are units of connection fo

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Practice Questions ECM and Nucleus (T or F) Connexons are units of connection for the adhesive junctions (T or F) Pathogens such as viruses and bacteria can use cell surface adhesion molecules to gain entry into the host cell:s (T or F) The cytoplasmic domain of an integrin is connected to cytoskeleton (T or F) The extracellular domain of an integrin can bind to components of the extracellular matrix (ECM) (T or F) The nucleolus is a site for rRNA synthesis 1. 2" 3. 4. 5. 6. Movement of animals is dependent on skeletal muscle. The ability of muscle to contract is dependent on the structural organization of muscle fibers What is the fundamental contractile unit of skeletal muscle, which is composed of bands, lines, and a zone? Sarcomere What are the letters that describe the bands, lines, and the zone? A and I Z and M During contraction the length of the muscle shortens due to changes within the contractile unit. What C. are the changes that take place with respect to the bands, lines, and the zone? See the Sarcomere slide with the table to right for the answers to these 7. A large protein of 120kD that shuttles between the nucleus and the cytoplasm contains a NLS at its N-terminus and a NES at its C-terminus. In normal cells, the steady state localization of the protein is cytoplasmic because the rate of its export is much faster than the rate of its import. Predict the localization of the protein under the following circumstances (answer with either "nuclear" or "cytoplasmic") a. The protein is mutated to have an intact NLS but a non-functional NES b. The protein is mutated to have an intact NES but a non-functional NLS The protein is mutated so that neither the NLS nor the NES is functional C (protein made in the C, not able to going into N, so it stays in C for such a large protein) c. d. The protein is put into cells without any importins in the cells e. The protein is put into cells without any exportins in the cells f. The protein is put into cells where there is no RanGTP in the cells N (RanGTP is required for nuclear export)

Explanation / Answer

NLS or nuclear localization signal helps the protein from nuclear import. This NLS is detected by importin protein, present in the cytoplasm, and thus importin helps the NLS comprising protein for nuclear import.

NES or nuclear Export signal helps the protein for export from nucleus This NES is detected by exportin protein, present in the nucleus, and thus exportin helps the NES comprising protein for exit from the nucleus.

Thus this protein shuttle between nucleus and cytoplasm. If NLS or NES is mutated then protein will not be able to move freely between nucleus and cytoplasm

A- In this case Protein can enter nucleus but due to the mutation in NES, it cannot come out of the nucleus to the cytoplasm. So protein will remain in the nucleus

B- In this case Protein cannot enter the nucleus and will be localized in the cytoplasm only.

C- In this case protein will remain in the cytoplasm as it is being synthesized in the cytoplasm.

D- Importin helps in the import of protein which has NLS. So in absence of importin protein cannot be moved to the nucleus. So it will remain in the cytoplasm.

E- Exportin help in the export of protein which has NES. So in absence of exportin protein cannot be moved out of the nucleus. So it will remain in the nucleus.

F- When the NLSconrtiaing protein reaches the nucleus, RanGTP helps in the release of protein from importin. In the absence of Ran-GTP protein will remain in the nucleus in complex with importin protein. Also, RanGTP helps exportin protein to export NES containing protein from nucleus to cytoplasm.

So protein will remain in the nucleus

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