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Exam 2 - Fall06 - BCH 3023 Fall 2006 Exam 2 BCH 3023 Name...

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BCH 3023, Fall 2006 Exam 2 BCH 3023                                         Name ______________________________________ Fall Semester, 2006 Exam 2                                              ID      ______________________________________ FORM A Bubble in the Test Form Code circle on your scantron with the Form Letter shown above. Bubble in your name and student ID on the scantron.  Sign the scantron using your normal  signature. No electronic devices may be used (or visible on your desk) during the exam. KEEP YOUR SCANTRON FACE DOWN EXCEPT WHEN RECORDING AN ANSWER. DO NOT MARK YOUR EXAM IN SUCH A WAY THAT OTHERS CAN DISCOVER YOUR  ANSWERS.     YOU   MAY   OTHERWISE   WRITE   ANYWHERE   ON   YOUR   EXAM   FOR  SCRATCH WORK. TURN IN BOTH EXAM AND SCANTRON AT THE END OF THE EXAM. 1.   The titration of the tripeptide, Glu-Cys-Gly, exhibits four pK a   values:   pK 1   = 2.0,   pK 2  = 3.6, pK 3  = 8.6, and pK 4  = 9.2.  What is the isoelectric point for this peptide? a.)  pH = 1.2 b.)  pH = 2.8 c.)  pH = 5.9 d.)  pH = 6.1 e.)  pH = 8.9 The fully protonated peptide would have a single positive charge (the ionizible groups  would be in the forms: -COOH, -COOH, -SH, and –NH 3 + ). At pH = 2.0 the alpha carboxyl would be  ½  ionized (net total average charge = +  ½  ). At pH = 3.6 the carboxyl group would be more or less fully ionized and another group  would become  ½  ionized, you don’t have to know what group it is.  The net average  charge on this group would be - ½     and the net total average charge would be: +1 -1 – ½   or –  ½  .  The isoelectric point would be the average of the pKa’s 2.0 and 3.6. Page 1 of 11
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BCH 3023, Fall 2006 Exam 2 2.  Which of the following monosaccharides is a hemiketal? Ribose, glucose and galactose are all aldoses and form hemiacetals,  Fructose is a ketose  and forms a hemiketal. 3 .    32 P is a radioactive isotope of phosphorus that is  commonly used  in  biomedical  research.  The half-life of  32 P is 14 days.  How long does it take for 90% of the original level  of 
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