Exam 1-2004Key

Exam 1-2004Key - BIO 361 EXAM 1 FALL 2004 NAME:_ ID:_ 1....

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BIO 361 EXAM 1 FALL 2004 NAME:_________________________________________________ ID:_____________________________________________________ 1. Write Your name and ID on all pages 2. Write all answers in pen only 3. Try to limit your answers to the space provided 4. Make sure your exam has six pages including this cover page Page 2 _______________ Page 3 _______________ Page 4 _______________ Page 5 _______________ Page 6 _______________ Total _______________ Maximum of 110 points
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NAME:_________________________ ID:_________________________ 2 1. Shown below is a modified tripeptide, which resembles the chromophore of red fluorescent protein. The backbone looks unusual because of a cyclization reaction, which is accompanied by a dehydration reaction. (a) Identify (by circling all available atoms) and name the three residues that make up the chromophore. (b) What is the overall charge of this peptide at pH 2 and pH 12? (c) Calculate the pI of this tripeptide. For (c) show how you derived your answer. (12 points) (b) pH 2: +1 and pH 12: -2 (c) pI = (3+8)/2 = 5.5 The pI is at the midpoint between the pK a of the α -carboxy group and the pK a of the α -amino group. 2. The sequence Leu-Ile-Thr-Thr-Ala-His-Ala has been found to adopt an α -helix in one protein and a β -strand in another. (a) Approximately how far apart will be the first and last residue in both conformations? Show how you derived your answer. (b) Label each residue either with α or β according to its secondary structure preference. (10 points) (a) α -helix: rise per residue is 1.5 Å; for six residues (from 1 to 7): 6 x 1.5 Å = 9 Å β -strand: translation per residue is 3.3 Å; for six residues: 6 x 3.3 Å ~ 20 Å (b) Leu-Ile-Thr-Thr-Ala-His-Ala α β β β α α α COO - N O N NH 3 + H 2 N HO O Gln Tyr Gly
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NAME:_________________________ ID:_________________________ 3 3. The following data were recorded for an enzyme obeying Michaelis-Menten kinetics: [S] in M V 0 in nmoles x liter -1 x min -1 6.25 x 10 -6 15.0 7.5 x 10 -5 56.25 1 x 10 -4 60 1 x 10 -3 74.9 1 x 10 -2 74.99 (a) Estimate V max (b) Calculate K M (c) (c) What would V 0 be at [S] = 1 x 10 -4 M if the enzyme concentration were doubled? Show how you derived your answers. (12 points) (a) V max will be approached asymptotically at high substrate concentrations, a reasonable estimate is therefore 75 nmoles x liter -1 x min -1 . (b) Using the value for V
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Exam 1-2004Key - BIO 361 EXAM 1 FALL 2004 NAME:_ ID:_ 1....

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