Which peptides would have the greatest solubility in water at pH 7? a. AAAAA b.

Question

Which peptides would have the greatest solubility in water at pH 7?

a. AAAAA

b. KKKKK

c. EAAAK

d. KAAAE

e. impossible to tell.

2. The specific activity of a enzyme mixture

a. increases as the protien is purified

b. decreases as the protien is purified

c. Can be used to assess the homogeneity of fractions across a chromatographic peak

d. A and C

e. B and C

3. You are trying to separate a protein X from Protein Y. X is a homo-dimer of 50 kDa subunits with a pI of 8. Protein Y is a 40kDa monomer with a pI of 5. Which of the following separation results make sense?

a. On SDS-PAGE X migrates faster

b. On Gel filtration chromatography X elutes first

c. On Cation exchange chromatography at pH 7 X elutes first.

d. All of the above

e. None of the above

4. Ionization of proteins in Electrospray Mass spectrometry at acid pH results in

a. A family of species with different charges and slightly different molecular Masses

b. A family of species with different charges but the same molecular Mass

c. A single molecular species

d. Fragmentation of peptides at random positions

e. Fragmentation of peptides at specific amino acid sequences

Explanation / Answer

1. e. impossible to tell.

Since none of the sequence contains polar amino acids therefore, it is impossible to tell which peptides will be more soluble.

2. a. increases as the protein is purified

Due to the removal of inactive protein the specific activity is increased.

3. d. All of the above

All of the given statements are correct.

4. d. Fragmentation of peptides at random positions

Ionization leads to structural destruction of peptide.

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