Online_Tutorial2_Key - [3 points] 2. What is the...

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Biol 2040U- Winter 2009 On-line Tutorial assignment # 1 Use your textbook and lecture notes to answer the following four (4) questions. Print this out, and work on it. Hand this to your TA by 5:00 pm Thursday January 29 th to them or in their drop boxes. 1. The enzyme ribonuclease A has a total of 4 disulfide bonds. A former scientist demonstrated that if all the disulfide bonds in ribonuclease were reduced and the enzyme unfolded in urea, then upon removal of both the urea and the reducing agent at the same time, the enzyme spontaneously refolded to its native active tertiary structure with the correct disulfide bonds. In a different experiment, the scientist allowed reoxidation to occur first, but only when the denaturant (urea in this case) was still present. After reoxidation, then the urea was removed appropriately. What would happen to the overall structure of the enzyme in this two step procedure.
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Unformatted text preview: [3 points] 2. What is the isoelectric point (pI) of oxytocin, which is shown below? Use the table in your book to locate the appropriate pKas. How many stereocenters are present on this molecule? In a different experiment, strong conditions have broken the disulfide bridge. Once this occurs, will the pI increase, decrease, or remain unaffected relative to its native pKa. Justify your reasoning [3 points] 3. Selenocysteine is shown below and the pKa of the side chain is 5.3. It is a naturally occurring unusual amino acid. Draw the titration curve for this amino acid between pH 0 - 14, and be sure to indicate where the isoelectric point lies (calculate pI to one decimal place). Make clear in your graph where half- and full equivalents of [ – OH] lie. Also, why would the pKa of selenocysteine be much lower than that of cysteine? [4 points]...
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This note was uploaded on 02/26/2010 for the course BIOCHEM CHEM1000 taught by Professor Hemstead during the Spring '09 term at York University.

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Online_Tutorial2_Key - [3 points] 2. What is the...

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