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Unformatted text preview: NAME: ___________________________________ 2006 TF: ________________________________________ Biological Sciences 54 EXAM 2 A. Be sure to write your name on the top of each of page of the examination. B. Write each answer only on the same page as the pertinent question. THE SPACE PROVIDED IS MEANT TO BE SUFFICIENT BE CAREFUL & BE CONCISE. If absolutely necessary, use the back of that page to continue the answer. C. IF YOUR ANSWER CANNOT BE READ IT CANNOT BE GRADED. D. Remember, if you do not show your reasoning, you cannot get partial credit. E. The point value for each question is noted. ALLOCATE YOUR TIME WISELY. F. Read carefully, think before you write, good luck, and do well! page 2: __________ (25 pts) page 3: __________ (25 pts) page 4: __________ (25 pts) page 5: __________ (25 pts) TOTAL: _______ (100 pts) Name ____________________________________ TF________________________________ 2 1. (16 pts) Glycogen breakdown occurs a short time after epinephrine binds to its receptor. A) At what point in this pathway is there a significant amplification of the signaling process that originates in epinephrine binding to the extracellular domain of its cognate receptor? How is the amplification accomplished? Phosphodiesterase (PDE) is an enzyme that downregulates cAMP levels. PDE contains the following amino acid sequence motif: X-R-R-X-S-f. You want to test how mutations in this motif affect cAMP levels. You transfect wild type cells with cDNA encoding either wild type or PDE with S (serine) mutated to D (aspartic acid, mimics phosphorylated serine), then you assay for levels of cAMP. The following results are found. B) Use the data and what you know about cAMP production to explain the normal regulation of PDE and how the S-to-D mutation affects cAMP levels when Adenylyl Cyclase (AC) or Protein Kinase A (PKA) are directly activated. 2. (9 pts) TGFbeta signaling is critical in many developmental processes. There are three types of receptors (Type I, Type II, and Type III), all of which are necessary for a normal response to the growth factor. Outline the events that occur after cells expressing these receptors are exposed to TGFbeta. Include all details significant for this signal transduction pathway up to the point of Smad phosphorylation. You may use a series of diagrams....
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This note was uploaded on 04/07/2008 for the course MCB 54 taught by Professor Lue during the Fall '06 term at Harvard.
- Fall '06
- cell biology