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Lecture 24.docm

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Gerald Cupchik

Lecture 24 Question 1 - 690 Response of a cell to multiple signals depends on: effectors/adaptors/kinases/phosphatases present positive and negative influences of the signaling molecules the integration of signals to finely tune the response only one of the above is true all of the above is true E is correct, because STP depends on receptor type, and the integration of all positive and negative signals for a given cell (refer. Lecture 24, Slide 15) Question 2 - 674 Which of the following statements is true in regards to Receptor protein-Tyrosine Kinases and the MitogenActivated Protein kinase cascade? Raf, MEK, ERK, and MKP all undergo phosphorylation throughout the cascade Grb2 acts as an adapter on Ras-GDP to convert the molecule into its active Ras-GTP form Once activated, MAPK translocates into nucleus where it phosphorylates MAP kinase phosphatase, facilitating cell proliferation Without the presence of a receptor, the MAP kinase cascade can still progress as long as there is a growth factor (ligand) present None of the above A. FALSE. Although all 4 molecules have to do with the cascade and RTKs, only Raf, MEK, and ERK are actually phosphorylated by MAPKK, MAPKK, and MAPK. MKP does the opposite to this and removes phosphate groups off of MAPK to terminate the signal (Riggs, lecture 24, slides 6-7) B. FALSE. Grb2 is solely an adaptor protein. The molecule mainly responsible for the conversion of Ras-GDP to an active form is Sos, which is a GEF (guanine nucleotide exchange factor) that exchanges GTP for GDP. Sos, through binding to Grb2, activates Ras-GDP to Ras-GTP. (Karp, Ch. 15, Pg. 628) C. FALSE.Although it is true that once MAPK has been phosphorylated it moves into the nucleus, it does not phosphorylate MKP, but rather Transcription Factors to promote cell proliferation. MKP is crucial for opposing this signal continuation. (Riggs, lecture 24, slide 7) D. FALSE. Areceptor must be present in order for the ligand, in this case a growth hormone, to bind. Without the receptor, there is no transautophosphorylation that occurs, which in turn does not recruit the necessary proteins for the cascade. (Riggs, lecture 24, slide 4) E. TRUE.All other answers were false, but with only slight modifications to each answer. Be careful! Think it through! Question 3 - 681 Caspases are a group of cysteine protease that are capable of cleaving a select group of essential proteins. Which protein(s) is/ are the target of caspases? Protein kinases Lamin Hi
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