Biochemistry 410 Midterm Exam 1 Form B Make sure you have 12 pages including the title page Make sure to mark Form A on your Scantron Turn it your entire exam with your Scantron Note All cell phones must be turned off and put completely away Using a programmable calculator on this exam is cheating No disruptive behavior or wandering eyes during exam time will be tolerated I wish you all great success 1 What statements are correct about cysteine It is aromatic non polar amino acid i ii Cysteine has C one letter abbreviation iii N terminus pKa is 8 5 while R group pKa is 8 iv C terminus pKa is 2 while R group pKa is 6 v Cysteines make disulfide bonds a b c d e ii iv v ii v i iii iv ii iv v iii iv a STRA and VDEA b KHCF and PARS c CKSA and KCTG d AVAR and ERTA e None of the above 2 What statement correctly describes the difference between Phe and Tyr a At physiological pH Phe is a zwitterion while Tye has net negative one charge b Phe is aromatic while Tyr is not c One OH group d These two amino acids have different C and N termini pKa e Phe is commonly found in a helix while Tyr has a high propensity presence of b sheets 3 Select two peptide pairs that would have the net charge of 3 at pH 11 4 A titration curve shown above can be used to explain protonation deprotonation of which pairs of compounds i Histidine ii Proline iii Cysteine iv Phenylalanine v H3PO4 a b c d e i ii ii iv iv v i iii v ii iii v 5 In the case of Thr Point A would be equal to a 12 b 9 c 8 5 d 13 e 10 6 What is the pH of a solution containing 1 8 x 10 3M HCl a 2 5 7 At what pH range His has net 2 charge b 2 5 c 2 7 d 5 8 e 3 0 a Below pH 2 b From pH 2 to pH 6 c From pH 6 to pH 9 d From pH 8 to pH 9 e Above pH 9 a His and Ala b Lys and Arg c Arg and Cys d Val and Phe e Phe and Tyr 8 Which pair of amino acids will have opposite absolute chiral configuration 9 AHAS FPFIGQQG and VVWTPPHCDNNR peptides are loaded in the column with carbohydrate polymer beads gel filtration What is the expected elution sequence of these peptides a AHAS FPFIGQQG and VVWTPPHCDNNR b FPFIGQQG AHAS and VVWTPPHCDNNR c VVWTPPHCDNNR AHAS and FPFIGQQG d VVWTPPHCDNNR FPFIGQQG and AHAS e AHAS VVWTPPHCDNNR and FPFIGQQG 10 What is the protein concentration if the solution of protein has an absorption of 0 5 The extinction coefficient is 1000 cm 1 M and measurements were done in the cell with 0 5 cm pathway a 0 1 mM b 1 mM c 0 05 M d 0 1 M e 8 M 11 What secondary structure can the protein adopt if 60 and 60 a Antiparallel sheet b Parallel sheet c Collagen triple helix d Closed ring e Left handed alpha helix 12 helix has 30 amino acid residues Calculate how many Angstroms the helix would cover a 45 b 20 c 22 7 d 50 e 21 13 Which statement incorrectly describes helix a In helix the peptide C O bond of the nth residue hydrogen bonds with the peptide N H group of the n 4 th residue b helix is primarily stabilized by hydrogen bonding c Ala or Asp destabilizes a helix d String of Asp Glu Lys or Arg at neutral pH destabilizes helix e All statements are correct 14 What statement correctly describes both keratin and collagen a Both keratin and collagen are globular proteins b Prolines in keratin can be hydroxylated to 4 hydroxyprolines whereas collagen possess a high amount of disulfide bonds c Keratin has around 33 Gly whereas collagen is dominated by Phe d Collagen is a triple helix Hard keratins have high sulfur content and can be found in hair horn and nail e None of the statements is correct 15 What chemical modifications lead to the transformation of His to histamine a Hydroxylation and deamination 16 What is pI for the following peptide at physiological pH Val Ser Cys Phe b Esterification and protonation c Decarboxylation d Decarboxylation and dihydroxylation e Dopamine cannot be formed from Tyr a 5 5 b 9 5 c 2 85 d 6 1 e 3 8 Ion exchange with CM modified cellulose Ion exchange with DEAE modified cellulose PFYYAAGVCC a b c Gel filtration d Affinity chromatography e Salting out 17 What separation technique would you prefer to use to purify KKRHPPVAKR from DDEPADADV and 18 what is the phenotypic appearance of Ehlers Danlos Syndrome a Hyperextensibility of the joints and skin b Defects in Type I collagen c Formation of spots on the skin spongy gums and bleeding from the mucous membranes d Memory loss e Anemia 19 What is the major physiological function of Hsp70 a ion transport b protein folding c peptide bond hydrolysis d posttranslational modification of proteins e this molecule does not exist 20 what posttranslational modifications are found in proteins i hydroxylation and methylation ii deamination and esterification iii phosphorylation and adenylylation iv acetylation and acylation a b c d e i ii iii i iii iv iii iii iv ii 21 What is the expected function of a protein domain shown in yellow a protein anchoring in membranes b regulatory function c catalytic function d protein binding e all of the above 22 Which of the following physical factors cannot cause protein denaturation a high temperature b pH c detergents d chaotropic agents e all of the above 23 What statement correctly describes Protein Disulfide Isomerase PDI a it is a protein that catalyzes the rearrangement of a polypeptide s non native disulfide bonds b PDI is involved in protein folding c PDI can exist in two states oxidized and reduced d oxidized form of PDI catalyzes the initial formation of a polypeptide s disulfide bonds e all of the above Ag2O s 2Ag s 1 2O2 g 24 The temperature at which the reaction given below is at equilibrium is Given that Ho 40 kJ mol 1 and So 0 1 kJ K 1 mol 1 25 Identify homo peptides from all listed below a 410K b 400K c 0 00025K d 40K e 4K i ii iii iv v 4 Lys His His His P A P A His Ala AGGAT a i iii b iii iv v c i ii iii d i ii e iii v a 4 74 b 7 44 c 4 4 d 4 74 e 0 26 Ka of acetic acid is 1 8 x 10 5 What is pKa 27 Calculate the pH of a formic buffer containing 100 mM acetic acid and 0 2 M sodium acetate The pKa of formic acid is 2 76 a …