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Ch 22 Amino Acids & Proteins

Ch 22 Amino Acids & Proteins. 1. Identify the following amino acids:. Ch 22 Amino Acids & Proteins. 2. Draw L- and D-threonine. Ch 22 Amino Acids & Proteins. 3. Circle the correct answer: a. If the pH < pKa [HA] > [A - ] [HA] = [A - ] [HA] < [A - ] b. If the pH > pKa

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Ch 22 Amino Acids & Proteins

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  1. Ch 22 Amino Acids & Proteins 1. Identify the following amino acids:

  2. Ch 22 Amino Acids & Proteins 2. Draw L- and D-threonine.

  3. Ch 22 Amino Acids & Proteins 3. Circle the correct answer: a. If the pH < pKa [HA] > [A-] [HA] = [A-] [HA] < [A-] b. If the pH > pKa [HA] > [A-] [HA] = [A-] [HA] < [A-] c. If the pH = pKa [HA] > [A-] [HA] = [A-] [HA] < [A-]

  4. Ch 22 Amino Acids & Proteins 4. Draw the predominant form of alanine as a function of pH (from 0 to 14) 0 7 14

  5. Ch 22 Amino Acids & Proteins 5. Calculate the pI of: (assume the pKa’s of –COOH and –NH3+ groups are 2 and 9.5 respectively) a. valine b. aspartic acid (pKa of side chain = 3.9) c. arginine (pKa of side chain = 12.5)

  6. Ch 22 Amino Acids & Proteins 6. Circle the correct answer: • As pI increases, the AA is: more basic or more acidic • If pH < pI, the AA is: net positive, net negative or neutral • If pH > pI, the AA is: net positive, net negative or neutral • If pH = pI, the AA is: net positive, net negative or neutral • At a given pH, the higher the pI, the AA is more: positive or negative • At a given pH, the lower the pI, the AA is more: positive or negative

  7. Ch 22 Amino Acids & Proteins 7. For the following fingerprint obtained by electrophoresis and chromatography, label the amino acids (ser, glu, val, his, met, thr) that would be at each spot: chromatography  Electrophoresis pH =5

  8. Ch 22 Amino Acids & Proteins 8. Illustrate the synthesis of valine using the different methods: • HVZ reaction with amination • Reductive amination • N-phthalimido synthesis (Gabriel & malonic ester synthesis) • Strecker synthesis

  9. Ch 22 Amino Acids & Proteins 9.Illustrate a peptide synthesis of val-ser-ala using: • Reagents in solution • Automated solid-phase (Merrifield) synthesis

  10. Ch 22 Amino Acids & Proteins 10. A nonapeptide undergoes partial hydrolysis to give peptides whose amino acid compositions are shown below. Reaction of the intact nonapeptide with Edman’s reagent releases PTH-Leu. What is the sequence of the nonapeptide? a. pro,ser e. glu,ser,val,pro b. gly,glu f. glu,pro,gly c. met,ala,leu g. met, leu d. gly,ala h. his,val

  11. Ch 22 Amino Acids & Proteins 11. Determine the amino acid sequence of a decapeptide from the following results. a. Acid hydrolysis gives ala, his, gly, 2 lys, 2 met, phe, ser, val b. Carboxypeptidase B releases an amino acid, but carboxypeptidase A does not c. Edman’s reagent releases PTH-His d. Cleavage with cyanogen bromide gives 1. his, lys, gly, met, ser 2. lys, val 3. ala, phe, met e. Trypsin-catalyzed hydrolysis gives 1. gly, his, lys 2. ala, 2 met, lys, phe, ser, val f. Chymotrypsin-catalyzed hydrolysis gives a hexapeptide and a tetrapeptide

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