UMD BCHM 461 - Paukstelis_Exam1_461_Spring17 (8 pages)

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Paukstelis_Exam1_461_Spring17



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Paukstelis_Exam1_461_Spring17

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Pages:
8
School:
University of Maryland, College Park
Course:
Bchm 461 - Biochemistry I

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BCHM 461 0101 March 7 2017 Dr Paul Paukstelis Name 1 Exam 1 Exams written in pencil or erasable ink will NOT be re graded under any circumstances The University of Maryland Honor Pledge The Honor Pledge is a statement that University of Maryland students are required to agree to on all examinations The Pledge reads I pledge on my honor that I have not given or received any unauthorized assistance on this examination After you have completed this examination sign your name to acknowledge that you agree to this pledge BCHM 461 0101 March 7 2017 Dr Paul Paukstelis Name 2 Exam 1 100 points 1 20 points Bioenergetics and Nucleic Acids a For both GMP and dGMP the standard free energy change DG o for the conversion from Pucker A to Pucker B shown below is a very small though non zero value In just one or two sentences explain what this would mean generally about the distribution of these different sugar puckers in an equilibrated solution and why b In the box provided identify the sugar puckers using the appropriate naming scheme In plane atoms are shown by the line running roughly through their centers c When the DG o for the same pucker conversion is determined for GMP and dGMP now as part of a nucleotide chain that forms an RNA or DNA duplex the value is negative for dGMP but much more positive for GMP In two or three sentences describe a likely reason for this in the context of the duplex structures Name 3 BCHM 461 0101 March 7 2017 Dr Paul Paukstelis 2 30 points Acid Base Chemistry and Amino Acids a Homocysteine shown below in its non ionized form is an amino acid similar to cysteine The pKa s for the L homocysteine functional groups are similar but distinct from those of L cysteine The chart below shows a comparison Provide analysis for WHY these are different You may draw or reference the image if that assists you but make sure your answer is specific L cysteine L homocysteine pK1 COOH 1 96 2 3 pK2 NH3 10 28 9 0 pKR 8 18 10 0 b You are working with a peptide of the sequence TAGYERIT 1 Using the method we used in class estimate the isoelectric point of this peptide 2 When a titration of this peptide is performed it turns out that the measured isoelectric point is 7 2 Based on this a Overall will the peptide carry a positive or negative charge at neutral pH Explain your answer in general terms BCHM 461 0101 March 7 2017 Dr Paul Paukstelis Name 4 b Describe two reasons why pI estimates are often times much different than the experimental values Your answer can be general but you can use the above peptide to highlight your point c This photo was posted on the March for Science April 22 nd on the Mall see you there facebook group a couple of



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