Chapter 8: Mechanisms and Inhibitors (Test 2)

Question 1

• Chymotrypsin is has best specificity with

Answer 1

• Phenylalanine
• Tryptopan
• Tyrosin

Question 2

What is required for chymotrypsin activity?

Answer 2

• Serine 195

Question 3

What is chymotrypsin?

Answer 3

• A proteolytic enzyme that hydrolyzes peptide bonds selectively on the carboxyl side of large hydrophobic amino acids?

Question 4

Which organ secretes chymotrypsin?

Answer 4

• The pancreas

Question 5

What is diisopropylphosphofluoridate (DIFP)?

Answer 5

• The group-specific reagent that modifies only serine 195, one of 28 serine residues in chymotrypsin, and inhibits the enzyme

Question 6

What is a chromogenic substrate for chymotrypsin?

Answer 6

• N-Acetyl-L-phenylalanine p-nitrophenyl (ester)

Question 7

What comprises the catalytic triad that includes serine?

Answer 7

• Serine
• Histidine
• Aspartic Acid

Question 8

What are common catalytic strategies?

Answer 8

• Covalent catalysis
• General acid-base catalysis
• Metal ion catalysis
• Catalysis by approximation and orientation

Question 9

What is covalent catalysis?

Answer 9

• The active site contains a nucleophile that is briefly covalently modified

Question 10

What is general acid-base catalysis?

Answer 10

• A molecule other than water donates or accepts a proton

Question 11

What is metal ion catalysis?

Answer 11

• Metal ions function in a number of ways including serving as an electrophilic catalyst

Question 12

What is catalysis by approximation and orientation?

Answer 12

• The enzyme brings two substrates together in an orientation that facilitates catalysis

Question 13

What are the three common types of reversible inhibition?

Answer 13

• Competitive inhibition
• Uncompetitive inhibition
• Noncompetitive inhibition

Question 14

What is competitive inhibition?

Answer 14

• The inhibitor is structurally similar to the substrate and can bind to the active site, preventing the actual substrate from binding
• Can be overcome with a high concentration of substrate
• Vmax is unchanged, but Km is increased

Question 15

What is uncompetitive inhibition?

Answer 15

• The inhibitor binds only to the-substrate complex
• Vmax and Km are decreased
• Cannot be overcome

Question 16

What is noncompetitive inhibition?

Answer 16

• The inhibitor binds either the enzyme or the enzyme-substrate complex
• Vmax is decreases, Km is unchanged
• Cannot be overcome