In the catalytic mechanism of chymotrypsin what is

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45. In the catalytic mechanism of chymotrypsin, what is represented by the two hills in the reaction coordinate? A) His 57 acting as a base catalyst twice in the mechanism B) Water entering the active site C) The tetrahedral intermediates, where oxygen acts as a nucleophile attacking the carbonyl carbon D) His 57 acting as an acid catalyst, donates a proton to the nitrogen of the scissile peptide bond E) The departure of the C-terminal portion of the cleaved peptide Version 3 Page 6
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46. Bacteria of the genus Lactobacillus produce lactobacillic acid, a 19-carbon fatty acid containing a cyclopropane ring (see structure below). Would you expect that the melting point of this fatty acid would be closer to the melting point of stearate (18:0) or oleate (18:1)? H H \ C Z \/\/\/ CH-CH / \ COO - A) closer to oleate B) closer to stearate 47. The action of phospholipase C results in the formation of 2 second messengers. Which of these is lipid soluble? A) diacylglycerol B) phosphatidylinositol bisphosphate C) inositol trisphosphate D) cAMP 48. How many acyl groups are attached to a sphingosine backbone in order to form a sphingomyelin molecule? A) 0 B) 1 C) 2 D) 3 49. Which of the following would be likely to form a bilayer in a solution containing only the lipid indicated? cholesterol sphingolipids I) All of the above Section III: 18 points (3 points each) 50. Which of the following boxed areas are most likely to be part of the membrane spanning portion of the protein, glycophorin A. A LSITEVANIErInSSSITSKSYIISSQTND'IEECILDTMATPRABE VSEISVRTITYPPEEETGERITQLAHHISEPEIELIFGVMAGVIG I c TILLISYGERRLILKSPSMEEPIPSDTDVPIISSVEIENPETSIDQ D E A) A B) B C) C D) D E) E 51. In unstimulated T cells, a transcription factor called NFAT (nuclear factor of activated T cells) resides in the cytosol in a phosphorylated form. When the cell is stimulated, the cytosolic Ca 2 + concentration increases and activates a phosphatase called calcineurin. Activated calcineurin hydrolyzes a phosphate from NFAT, allowing it to be localized to the nucleus where it there stimulates the expression of genes needed for T cell activation. Based on your understanding of the cell signaling pathway involved, order the steps of this activation process. 1) There is an influx of Ca 2 + from the endoplasmic reticulum into the cytosol 2) G protein activates phospholipase C 3) Extracellular ligand binds to G protein coupled receptor 4) Extracellular ligand binds to receptor tyrosine kinase 5) Phosphatidylinositol bisphosphate is hydrolyzed 6) Ca 2 + ions bind to calmodulin 7) Calcineurin activates NFAT 8) Ca 2 +-calmodulin complex binds to calineurin Version 3 Page 7
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