Which reagent reduces disulfide bonds to sulfhydryl groups? Which chemical reagent promotes peptide bond cleavage on the C-side (carboxyl side) of Met residues? Identify the least conservative amino acid substitution, assuming that these two residues occur at the same position in two homologous proteins

1. Which reagent reduces disulfide bonds to sulfhydryl groups?

2-mercaptoethanol

2. Which chemical reagent promotes peptide bond cleavage on the C-side (carboxyl side) of Met residues?

cyanogen bromide

3. Identify the least conservative amino acid substitution, assuming that these two residues occur at the same position in two homologous proteins.

glu->lys

4. The amino acid sequence of which type of protein is likely to have changed the least during evolution?

A protein that has extensive interactions with other proteins and with DNA.

5. Which of the following statements is not true about the Bradford assay?

It involves an absorption maximum shift from 465 nm to 595 nm.

6. Which of the following statements is not true about SDS-PAGE:

Proteins are separated based on their size, shape and electric charge at a given pH.

7. Which of the following statements about affinity chromatography is not true:

The stronger the interaction between the ligand and the protein, the better the result of the affinity purification.

8. Which chemical reagent promotes peptide bond cleavage on the C-side (carboxyl side) of lysine and arginine residues if the next residue is not proline?

trypsin

9. What would be the order of elution (from first --> last) of the proteins carbonic anhydrase (pI = 7.0), carboxypeptidase B (pI = 6.2) and chymotrypsin (pI = 8.0) run on a CM (carboxymethyl) ion exchange column at pH 6.6 eluted with an increasing NaCl gradient:

carboxypeptidase B, carbonic anhydrase, chymotrypsin.

10. Ion-exchange chromatography

separation on the basis of charge