BIOL 0280 Midterm: Exam1 2006 key

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turquoisegnu128

31 Jan 2019

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1: [4] given that pk1 = 2; pk2 = 10; pkr = 4, draw the ionization states and calculate the pi of aspartate. Pi=2+4/2=3 pi = 3: [4] draw the structures of the amino acids phenylalanine and glutamate in the ionization state you would expect at ph 7. 0. Glutamate has a polar (hydrophilic) side chain, which forms hydrogen bonds with water. In contrast, phenylalanine has a nonpolar (hydrophobic) side chain. structures. : [3] a. 2: [4] draw the dipeptide ala-val at ph 7 (be certain to draw all hydrogens). Indicate on your drawing (above) the bond that has limited rotation. Among forces that stabilize native protein structures are: (a) disulfide bonds, (b) hydrogen bonds, (c) hydrophobic interactions, (d) ionic interactions, or (e) water cage. Amino acid examples for a-e: cysteine, b)ser, thr, tyr, gln, asp, glu, lys, arg, his,or asn, c) ala, val, leu,

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Answer the following questions concerning the polypeptides whose amino acid sequences are shown below. Explain your reasoning for all.

A) Gly-Ile-Trp-Leu-Ile-Ile-Phe-Gly-Val-Val-Ala-Gly-Val-Ile-Gly-Trp-Ile-Leu-Leu-Leu

B) Gly-Pro-Asp-Gly-Pro-Met-Gly-Pro-Ser-Gly-Pro-Arg-Gly-Pro-Glu-Gly-Pro-Asp-Gly

C) Gly-Met-Trp-Pro-Glu-Met-Cys-Gly-Glu-Pro-Ala-His-Val-Arg-Asp-Tyr-Pro-Leu-Leu

D) Gly-Met-Trp-Pro-Glu-Met-Cys-Gly-Glu-Pro-Ala-His-Val-Arg-Asp-Tyr-Cys-Leu-Leu

1. Which would be most likely to form an a-helical structure?

2. Which could have at least one disulfide bond?

3. Suppose that the first amino acid residue in peptide (1) were altered from Gly to Pro. Would you expect this change to have an effect on the secondary structure of this peptide? Why or why not?

Alpha helices and beta sheets have common structural motifs but can contain very different amino acid sequences. For each of the following, circle the correct structure that could form given that sequence.

A. phe-leu-val-gly-ser-phe-leu-tyr-leu-gly-met-trp-leu-leu-phe-ile

amphipathic a helix hydrophilic a helix hydrophobic a helix

B. Ile-ala-asn-thr-leu-gly-thr-ala-ile-gln-ser-ile-ala-cys-leu-leu

amphipathic a helix hydrophilic a helix hydrophobic a helix

C. ser-ile-gln-leu-thr-phe-asn-met-glu-ile-glu-ala-thr-ile-arg-phe

amphipathic b sheet hydrophilic b sheet hydrophobic b sheet

D. asn-thr-asp-ser-tyr-asp-met-thr-ser-his-thr-asn-leu-lys-thr-ser

amphipathic b sheet hydrophilic b sheet hydrophobic b sheet

Please help me with this question,

1. At pH 7.0, in what order would the following three peptides be eluted from a column filled with an anion-exchange polymer? Their amino acid compositions are:

Peptide A: Ala 10%, Glu 5%, Ser 5%, Leu 10%, Arg 10%, His 5%, Ile 10%, Phe 5%, Tyr 5%, Lys 10%, Gly 10%, Pro 5%, and Trp 10%.

Peptide B: Ala 10%, Glu 10%, Gly 5%, Leu 5%, Asp 10%, Arg 5%, Met 5%, Cys 5%, Tyr 5%, Phe 5%, His 5%, Val 5%, Pro 5%, Thr 5%, Ser 5%, Asn 5%, and Gln 5%.

Peptide C: Ala 5%, Val 5%, Gly 10%, Asp 5%, Leu 5%, Arg 5%, Ile 5%, Phe 5%, Tyr 5%, Lys 5%, Trp 5%, Ser 5%, Thr 5%, Glu 5%, Asn 5%, Pro 10%, Met 5%, and Cys 5%.

First off column: _______________ Second: _______________ Last off column: _______________

BIOL 0280 Midterm: Exam1 2006 key

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