Set 5 - Problem Set 5 Bi9 Cell Biology ...

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Unformatted text preview: Problem Set 5 Bi9 Cell Biology Instructions: * There are 3 Parts. * Be sure to cite any sources you use besides Molecular Biology of the Cell, lecture or recitation. If you use websites, include link and date accessed. * Type your answers. * Print and turn in 3 separate sheets. 1 sheet for each part. * DO NOT staple the sheets together. Write your FULL NAME on every page. * Problem Set 5 is due on Tuesday May 10th at 5 pm. A box will be available on the first floor of Broad to turn in your work. Part I: General signaling and GPCRs A. (4 points) In class we discussed how intracellular signaling could produce different responses. Two main types of effector proteins are metabolic enzymes and proteins that regulate gene expression. Which one provides a faster response faster and why? (1 ­2 sentences each) B. (6 points) Briefly (two sentences each) describe the three major classes of cell ­ surface receptors: Ion ­channel ­coupled, enzyme ­coupled and GPCRs in terms of how they convert the extracellular ligand ­binding event into an intracellular signal. C. (6 points) Explain how cholera toxin and pertussis toxin interact with the GPCR signaling cascade. (2 sentences each) D.(4 points) Explain how you could use pertussis toxin and cholera toxin to determine the function of a newly discovered GPCR. (3 ­4 sentences) Part II : Ca+2 signaling questions A. (5 points) Why is important for the ell to keep the concentration of Ca+2 low inside the cell? (2 sentences) B. (5 points) Describe briefly the main ways by which the cell keeps the concentration of Ca+2 low? What are the different sources of energy that drive them? C. (6 points) Explain the function of calmodulin in the activation of CaM ­Kinase II by which the kinase acts as a molecular memory device (Answer should be less than 7 lines) Part III : Receptor Binding Your colleague has two cell lines (A and B). Each seems to have different binding affinities for ligands. He generates the two binding curves below: Figure 1 A)(4 points) Figure 2 shows the same data used to generate Figure 1 on a different scale. From these two figures, determine the values for KD in cell ­line A and cell ­line B. Be sure to show your work. Hint: You need both Figure 1 and Figure 2 to solve this problem. Figure 2 B) (4 points) The two cell lines show different values for KD. Suggest two ways in which the cells might be different. (two sentences each) C) (4 points) How do the koff and kon rates compare between the cell lines? D)(4 points) For cell ­line A, calculate the fraction of receptors bound to ligand if the extracellular concentration is 5 x 10 ­12 M. Hint: Use your result from part A E) (8 points) Explain why normal extracellular concentrations of this ligand are small in comparison to KD. What would happen if the normal extracellular concentrations were close to KD?(6 ­8 lines) ...
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