Posted: December 17th, 2016

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.4

Chapter 16 Cell Communication 1) The endogenous GTPase activity of G-proteins serves to: (a) stimulate the activity of enzymes by producing energy. (b) synthesize cGMP as a second messenger. (c) synthesize GTP as an energy source (d) hydrolyze GTP returning the G protein to a pre-stimulated level of activity 2) G protein-coupled receptors activate G proteins by reducing the strength of GDP binding, allowing GDP to dissociate and GTP, which is present at much higher concentrations, to bind. How do you suppose the activity of a G protein would be affected by a mutation that causes its affinity for GDP to be reduced without significantly changing its affinity for GTP? 3) Should RGS (regulator of G protein signaling) proteins be classified as GEFs (guanine nucleotide exchange factors) or GAPs (GTPase activating proteins). Explain what role the activity (of RGS proteins) plays in modulating G-protein-mediated responses in animals. 4) Antibodies are Y shaped molecules that carry two identical binding sites (at the variable region). Imagine that you obtained an antibody that is specific for the extracellular domain of a receptor tyrosine kinase. If cells were exposed to the antibody, would you expect the receptor tyrosine kinase to be activated, inactivated, or unaffected? Explain… 5) Genes encoding mutant forms of a receptor tyrosine kinase can be introduced into cells that also express the normal receptor from their own genes. If the mutants genes are expressed at considerably higher levels than the normal genes, what will be the consequences for receptor-mediated signaling of introducing genes for the following mutant receptors? A. A mutant receptor tyrosine kinase that lacks its extracellular domain? B. A mutant receptor tyrosine kinase that lacks its intracellular domain? Chapter 17 Cytoskeleton 1) In general terms, what are the cellular functions of intermediate filaments, microtubules, and actin filaments? 2) The ?-tubulin subunit of an ??-tubulin dimer retains its bound GTP for a short time after it is added to a microtubule, yielding a GTP cap whose size depends on the relative rates of polymerization and GTP hydrolysis. A simple idea about microtubule growth dynamics is that the ends with GTP caps grow, whereas ends without GTP caps shrink. To test this idea, you allow microtubules to form under conditions where you can watch individual microtubules. You then sever (or cut) one microtubule in the middle using a laser beam. A. Would you expect the newly exposed plus and minus ends to grow or shrink? Explain. B. What do you expect would happen to the newly exposed plus ends if you were to grow the microtubules in the presence of an analog of GTP that cannot be hydrolyzed, and you then severed the microtubules in the middle with a laser beam? 3) 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? 4) The graph in the figure below shows the time course of the polymerization of pure tubulin in vitro. You can assume that the starting concentration of free tubulin is much higher than it is in cells. percentage of tubulin molecules in microtubules C time at 37oC A. B. 5) Explain the reason for the initial lag in the rate of microtubule formation. Why does the curve level out after point C? Match the following labels to the numbered lines on the figure below.