UMD BCHM 461 - Paukstelis_Exam1_461_Spring17 (8 pages)

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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 days ago Identify three things that are wrong with this drawing and justify each of them with one sentence in the space provided Two are easy one is harder stereochemistry is not one of them and and single residue can only count for one thing Thing 1 Thing 2 Thing 3 BCHM 461 0101 March 7 2017 Dr Paul Paukstelis Name 5 3 25 points Proteins Below is a sequence alignment of two related proteins Regions are defined by the boxes of amino acids and labeled The alignment is duplicated on the scratch page for you to work on a Which region has the highest similarity and what is it as a percent or fraction b Which region has the highest identity and what is it as a percent or fraction c Which region has the lowest similarity and what is it as a percent or fraction d If Protein 1 were cleaved with chymotrypsin what is the maximum number of fragments that would be present after complete cleavage e Of the peptide fragments generated from the chymotrypsin treatment which two write their sequences out would likely have the strongest interactions based solely on the amino acid properties of those peptides Justify your answer in one or two sentences BCHM 461 0101 March 7 2017 Dr Paul Paukstelis 4 25 points Thinking question Name 6 You are given solutions of the following macromolecules Mol 1 GUGUCGAUCGAAG epeak 170 3 mM 1 cm 1 Mol 2 GAUCGAAUUUCGAUC epeak 191 1 mM 1 cm 1 Mol 3 AFWLWGGFWP epeak 17070 M 1 cm 1 Mol 4 KTSAQCNAR epeak 110 M 1 cm 1 All four macromolecules are at equal concentrations and their absorbances are measured in a spectrophotometer All samples are in a salt solution buffer at pH 7 0 and measured at 4 C Peak refers to the wavelength with maximum absorbance A For the UV absorbance spectra below assign which molecule is associated with that spectra in the box and provide two reasons why you chose that molecule Name 7 BCHM 461 0101 March 7 2017 Dr Paul Paukstelis B What is the concentration of Mol 4 in micromolar as it is shown above Show your work Score 1 20 2 30 3 25 4 25 Total 100 BCHM 461 0101 March 7 2017 Dr Paul Paukstelis Name 8 THIS IS A SCRATCH PAGE DO NOT INCLUDE OR REFERENCE ANSWERS TO THIS PAGE THE VERY FIRST THING I AM GOING TO DO IS TEAR THIS PAGE OFF AND THROW IT IN A RECYCLING BIN


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