Feedback for Multiple Choice Quiz 16

  1. All serine protease have a reactive Serine residue.

  2. You should review the reaction scheme in Campbell.

  3. Ser 195 can only function effectively as a nucleophile if Asp 102 and His 53 act together to remove the proton from the Ser -OH.

  4. Both of these enzymes have finely tuned their active sites such that they are complementary to the substrates that bind tightly. Trypsin has a negatively charged residue to recognize Lys or Arg while Chymotrypsin has a hydrophobic pocket.

  5. Any rate enhancement corresponds to a reduction in the energy of ES‡. The free energy decrease of the transition state is RTlnK‡. This is calculated (at 300K) as follows:
    2.303*2.5*log1010 = 5.75*10 = 57.5 kJ/mol.

  6. Ser is the 1st nucleophile to attack the peptide bond. Water is the 2nd nucleophile. It attacks the acyl-intermediate.

  7. Serine, by itself, is a poor nucleophile. The His residue that is adjacent to the active site Serine activates the Serine by removal of the proton from its -OH sidechain.
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