ist Map detb Under typical conditions, many essential biochemicaleactions procee
ID: 57642 • Letter: I
Question
ist Map detb Under typical conditions, many essential biochemicaleactions proceed so slowly that life could not existd without the presence of e These mechanisms generally utilize the following strategies: improving the nucleophiles and electrophiles present in the catalytic R groups or substrates; stabilizing the extra electron density of the leaving group and stabilizing transition states es. Enzymes increase reaction rates through a wide variety of mechanisms Proteases are s that break down proteins by hydrolyzing peptide bonds. Chymotrypsin is a se found in the digestive tract that cleaves peptide bonds on the C-trinal side of large ydrophobic amino acids Depicted below are a peptide substrate and the three catalytic residues within the chymotrypsin active site Note that the 2-dimensional geometry is only roughly shown. R1 represents a large hydrophobic amino acid and R represents other amino acids. The R groups of the catalytic triad of aspartate (Asp 102), serine (Ser195), and histidine (His57) are shown. Select the atoms that act as nucleophiles and electrophiles in the acylation phase of the reaction. Scroll down for more of this question. Note: Selected atoms will turn green (undo by clicking again) Select the 2 atoms that act as nucleophiles in the acylation phase. Note: As shown below, the nucleophilic atoms might be weak nucleophiles, but they become strong in the process of catalysis Select the 2 atoms that act as electrophiles in the acylation phase NH NHExplanation / Answer
In the acylation phase ser195 and water molecule acts as nucleophile and His 57 and peptide substrate act as electrophiles.
The answer for the remaining part is
The alkoxide ion on Ser 195 is stabilized by hydrogen bonds with backbone amide groups.
The hydrogen bond network among the catalytic triad orients His57 and Ser 195 for proton transfer.
A water molecule in the active site acts as a proton relay for the transfer of Ser 195 hydroxyl group proton to His57
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