Biochemistry for Pharmaceutical Sciences II - PHRM 836 Quiz 1 Key ...

Biochemistry for Pharmaceutical Sciences II - PHRM 836Quiz 1 Key - September 4, 2012This key shows the correct answer underlined in Red and any explanation in Blue.[3 points] Which of the side chain of the following amino acids is NOT likely to be charged at physiological pH?AspGluLysArgTyrThe pK a of the side chain of tyrosine is about 10. At physiological pH (~7), tyrosine exists in at its neutral acidform.[3 points] Which of the following is a zymogen?TrypsinChymotrypsinThrombinFactor XPlasminFactor X is a zymogen. When it is activated by proteolysis, it is called factor Xa. Zymogens of trypsin,chymotrypsin, thrombin, and plasmin are trypsinogen, chymotrypsinogen, prothrombin, and plasminogen,respectively.[3 points] Which of the following statements on Bohr effect is NOT correct?Hb + 4O 2 Hb(O 2 ) 4 + nH +Hemoglobin releases protons upon binding to oxygen.Oxygen release from hemoglobin is promoted as pH drops.The oxygen-bound form has greater affinity for protons than the oxygen-free form.Upon oxygen release, hemoglobin is more protonated.The conformational change upon oxygen binding breaks ion pairs in hemoglobin.Upon oxygen binding, hemoglobin releases protons. This means that the oxygen-bound form has less affinityfor protons than the oxygen-free form and the oxygen-bound form is less protonated than the oxygen-free form.[3 points] A plausible transition state structure for amide hydrolysis by an enzyme is shown below. What would begroups X and Y for effective catalysis of the reaction?X: General base, Y: General baseX: General base, Y: General acidX: Hydrogen bond donor, Y: General baseX: Hydrogen bond donor, Y: General acidX: Nucleophile, Y: General base

The enzyme deprotonates water with a general base (Y) to increase the nucleophilicity of the water molecule.To facilitate the nucleophilic attack, the enzyme also polarizes the carbonyl group and stabilizes the partialcharge on the carbonyl oxygen with a hydrogen bonding donor (X).