Question 1

Discuss the structure of chymotrypsin.​

Accepted Answer

The answer of Discuss the structure of chymotrypsin.​...

Question 2

Discuss metal ion catalysis.​

Accepted Answer

The answer of Discuss metal ion catalysis.​...

Question 3

Aspartate proteases display a variety of substrate specificities, but normally they are most active in cleavage of peptide bonds:
A) on the carboxyl side of the basic amino acids.
B) on the carboxyl side of aromatic amino acids.
C) on the carboxyl side of small, neutral residues.
D) between two hydrophobic amino acid residues.
E) none of the above.

Accepted Answer

Aspartate proteases typically cleave peptide bonds between two hydrophobic amino acid residues, as they recognize and bind to hydrophobic regions of the substrate.

Question 4

Effective HIV-1 protease inhibitors should have all of the following characteristics EXCEPT:
A) effective delivery in sufficient quantities to the desired site(s) of action in the organism.
B) relative specificity for the HIV-1 protease.
C) a backbone −OH group that forms a weak association with the two active-site carboxyl groups of the protease.
D) results in inhibiting the production of new virus particles in cells of infected patients.
E) broad spectrum enough to be effective against mutant viral forms.

Accepted Answer

The characteristic of having a −OH group that forms a weak association with the two active-site carboxyl groups of the protease is not essential for an effective HIV-1 protease inhibitor.

Question 5

Which of the following are relevant to the reaction catalyzed by chorismate mutase?
A) the reaction involves a concerted intramolecular rearrangement of chorismate to prephenate during the synthesis of phenylalanine.
B) the enzyme catalyzed and uncatalyzed reactions follow almost identical routes
C) the enzymatic reaction is thought to involve transition state stabilization by 12 electrostatic and hydrogen bond interactions
D) the geometry of the enzyme active site is such that the difference in energy between ES and the near attack conformation is less than 1 kJ/mol
E) all of the above are true

Accepted Answer

All of the statements provided are true and relevant to the reaction catalyzed by chorismate mutase. This enzyme facilitates the rearrangement of chorismate to prephenate, a key step in the biosynthesis of the amino acids phenylalanine and tyrosine. The reaction pathway, both catalyzed and uncatalyzed, involves similar transition states, and the enzyme is known to stabilize the transition state through multiple interactions. The active site's geometry minimizes the energy difference between the enzyme-substrate complex and the transition state, making the reaction more efficient.

Question 6

Which of the following statements regarding enzymes is true?
A) stabilization of the transition state must be less than stabilization of ES for catalysis to occur
B) an enzyme mechanism is vastly different from the uncatalyzed reaction
C) binding of substrate to an enzyme often causes strain, thus promoting transition state formation
D) a random single displacement mechanisms requires that substrates bind to the enzyme in a specific order
E) none of the above

Accepted Answer

Binding of substrate to an enzyme can cause strain, which can promote transition state formation and thus catalyze the reaction. A and B are both false statements, while D is referring to an ordered sequential mechanism, and not necessarily true for all enzyme mechanisms.

Question 7

If the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex?
A) Val
B) Asp
C) Arg
D) Ser
E) Gln

Accepted Answer

Aspartic acid (Asp) is a negatively charged amino acid, so it would provide electrostatic destabilization of the ES complex if the substrate contained a negative charge.

Question 8

In the chymotrypsin reaction mechanism there is a low-barrier hydrogen bond (LBHB) formed between: A) Asp¹⁰² and Ser¹⁹⁵. B) Asp¹⁰² and His⁵⁷. C) His⁵⁷ and Ser¹⁹⁵. D) Ser¹⁹⁵ and carbonyl oxygen in the peptide bond. E) None of the above.

Accepted Answer

The low-barrier hydrogen bond (LBHB) in chymotrypsin mechanism is formed between Asp102 and His57. This interaction lowers the activation energy required for the nucleophilic attack of the serine residue in the active site on the peptide bond of the substrate. This activated serine forms the covalent intermediate which subsequently undergoes hydrolysis to release the products. Therefore, choice B, where Asp102 is interacting with His57, is the correct option. Choice A refers to Asp102 and Ser195, while choice C mentions His57 and Ser195, neither of which are correct. Choice D is also incorrect, as it refers to the carbonyl oxygen of the peptide bond and not the LBHB.

Question 9

If the transition state of an enzyme catalyzed reaction contained a positive charge, which of the following amino acids would most likely be present in the active site to aid in transition state formation?
A) Lys
B) Val
C) Asn
D) Glu
E) Cys

Accepted Answer

Glu (glutamic acid) has a negatively charged side chain at physiological pH, which can stabilize a positively charged transition state through electrostatic interactions.

Question 10

Discuss the chorismate mutase active site.​

Accepted Answer

The answer of Discuss the chorismate mutase active site.​...

Question 11

HIV-1 protease is different from most mammalian aspartic acid proteases in that it has:
A) two subunits each with a two-aspartate active site.
B) two subunits each contributing an aspartate to the active site.
C) two active sites on one protein.
D) two subunits, one with an active site, and the other with a regulatory activity.
E) none of the above.

Accepted Answer

HIV-1 protease is a homodimer, with each subunit contributing an aspartate residue to form the active site, distinguishing it from most mammalian aspartic acid proteases which typically have a single polypeptide chain with two aspartate residues in the active site.

Question 12

The mechanism of aspartate protease catalysis is proposed to be:
A) covalent nucleophilic catalysis.
B) covalent electrophilic catalysis.
C) specific base catalysis.
D) general base-general acid catalysis facilitated by a low barrier hydrogen bond.
E) all of the above.

Accepted Answer

Aspartate protease catalysis involves general base-general acid catalysis facilitated by a low barrier hydrogen bond.

Question 13

Explain transition-state analogs with an example.​

Accepted Answer

The answer of Explain transition-state analogs with an example.​...

Question 14

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.​

Accepted Answer

The answer of Discuss the forces involved in the destabilization...

Quiz 14: Mechanisms of Enzyme Action

Discuss the structure of chymotrypsin.​

Discuss metal ion catalysis.​

Aspartate proteases display a variety of substrate specificities, but normally they are most active in cleavage of peptide bonds:

Effective HIV-1 protease inhibitors should have all of the following characteristics EXCEPT:

Which of the following are relevant to the reaction catalyzed by chorismate mutase?

Which of the following statements regarding enzymes is true?

If the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex?

In the chymotrypsin reaction mechanism there is a low-barrier hydrogen bond (LBHB) formed between:

If the transition state of an enzyme catalyzed reaction contained a positive charge, which of the following amino acids would most likely be present in the active site to aid in transition state formation?

Discuss the chorismate mutase active site.​

HIV-1 protease is different from most mammalian aspartic acid proteases in that it has:

The mechanism of aspartate protease catalysis is proposed to be:

Explain transition-state analogs with an example.​

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.​

Discuss the structure of chymotrypsin.

Discuss metal ion catalysis.

Discuss the chorismate mutase active site.

Explain transition-state analogs with an example.

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.