In general, proteins are least soluble in water when pH is close to the _________

1. In general, proteins are least soluble in water when pH is close to the _________.

pI

2. Which of the following amino acids would be first to elute at pH 8.0 from an anion-exchange column?
   
   - lysine
   - alanine
   - glutamic acid
   - asparagine
   - glycine

Lysine

3. Which of these are commonly used to cleave peptide bonds in polypeptides?
   
   - 2-mercaptoethanol (β-ME)
   - dansyl chloride
   - iodoacetate
   - sodium dodecyl sulfate
   - trypsin

Trypsin

4. Which physical characteristic is not commonly used in protein separation?
   
   - solubility
   - stereochemistry
   - size
   - charge
   - polarity

Stereochemistry

5. Enzymes that hydrolyze the internal peptide bonds (not the peptide bonds of the terminal amino acids) of a protein are classified as _______.

Endopeptidases

6. In two homologous proteins, which residue is most likely to replace a Glu residue as a conservative substitution?
   
   - Asp
   - Trp
   - Met
   - Ile
   - Lys

Asp

7. The endopeptidase _____ cleaves polypeptides on the C-terminal side of certain bulky hydrophobic amino acid residues.

Chymotrypsin

8. A fast way for nature to generate new proteins is:

Shuffling protein domains or motifs.

9. ________ has emerged as a technique for protein sequencing.

Mass spectrometry

10. You have purified a new peptide hormone. To determine its amino acid sequence you have digested the polypeptide with trypsin and in a separate reaction you have cleaved the polypeptide with cyanogen bromide.
    Cleavage with trypsin yielded 5 peptides that were sequenced by Edman degradation as shown in the following.
    
    1. Ser-Leu
    2. Asp-Val-Arg
    3. Val-Met-Glu-Lys
    4. Ser-Gln-Met-His-Lys
    5. Ile-Phe-Met-Leu-Cys-Arg
    
    Cleavage with cyanogen bromide yielded 4 peptides that were sequenced by Edman degradation:
    
    1. His-Lys-Ser-Leu
    2. Asp-Val-Arg-Val-Met
    3. Glu-Lys-Ile-Phe-Met
    4. Leu-Cys-Arg-Ser-Gln-Met
    
    Determine the identity of the N-terminal amino acid after reconstructing the intact protein.

Asp