Essential Cell Biology Chapter 17 Exam Questions with Verified Answers

17-1) Which of the following types of cells would you expect to contain a high density of intermediate filaments in their cytoplasm? Explain. A. Amoeba proteus, B. Skin epithelial cells, C. Smooth muscle cells in the digestive tract, D. E. Coli, E. Nerve cell in the spinal cord, F. Sperm Cell, G. Plant Cell - ANSWER-Intermediate filaments help with tensile forces. Sperm cells and amoeba don't undergo tensile forces. E. coli has no filaments at all. And plant cells maintain their shape with a cell wall rather than with filaments. Epithelial cells, smooth muscle cells, and nerve cells all contain a high density of intermediate filaments in their cytoplasm. 17-2) Dynamic instability causes microtubules to either grow or shrink very rapidly. Consider a shrinking microtubule. A. What must happen at the end of the microtubule in order for it to stop shrinking and start growing again. B. How would a change in the tubulin concentration affect this switch? C. What would happen if only GDP, but no GTP, were present in the solution? D. What would happen if the solution contained an analog of STP that cannot be hydrolyzed? - ANSWER-A. It's shrinking because it's lost its GTP cap; You need to add a lot of GTP-loaded subunits in order to stop this, or else they will either hydrolyze their own GTP or fall off when the rim around them disassembles B. The rate of addition of GTP-tubulin will be greater at higher tubulin concentrations. Additionally shrinking microtubules release tubulin, so more shrinking microtubules actually causes a higher frequency of growing microtubules C. The microtubules would shrink and then disappear, because tubulin dimers with GDP have a low affinity for one another D. The microtubules will continue to grow until there are no more tubulin dimers left to use. 17-2) Why do you suppose it is much easier to add tubulin to existing microtubules than to start a new microtubule from scratch? Explain how y-tubulin in the centrosome helps to overcome this hurdle. - ANSWER-Because two individual tubulin dimers have a low affinity for each other. The tubulin has more opportunity to interact and bind with the large microtubule structure than with a tubulin dimer. y-tubulin rings help to make sure enough tubulin dimers come together at the same time to form a microtubule. Dynein arms in cilium are arranged so that, when activated, the heads push their neighboring outer doublet outward toward the tip of a cilium. Why would no bending motion of the cilium result if all dynein molecules were active at the same time? What pattern of dynein activity can account for the bending of a cilium in one direction? - ANSWER-The physics wouldn't work, there would be no significant relative motion (two people trying to lift each other off of the ground do not levitate). A few ciliary dynein molecules must be activated selectively on one side of the cilium. As they move their