7. What kind of process is represented in the following equation?
A. Hydrogenation
B. Substitution
C. Decomposition
D. Addition and elimination
Answer: A
Clarification: The process in the above reaction represents simple hydrogenation process to form aspartame. If BOC-L-aspartic acid and L-phenylalanine methyl ester are reacted in the presence of thermolysin, an equilibrium reaction mixture is achieved producing relatively small yields of BOC-aspartame. After this step, the BOC-aspartame is released from this adduct by simply altering the pH. The stereo-specificity of the thermolysin determines that only the L-isomer of phenylalanine methyl ester reacts but the addition product is formed equally well from both the D- and L-isomers.
8. Which of the following factor does not favor peptide synthesis?
A. Use of liquid/liquid biphasic systems
B. Selection of protecting residues for amino and carboxyl groups
C. Choice of pH
D. Location of proteases
Answer: D
Clarification: The following factor favor peptide synthesis which acts by controlling the equilibrium of the reaction:
• Choice of pH.
• Selection of protecting residues for amino and carboxyl groups which favor product precipitation.
• Use of liquid/liquid biphasic systems.
Location of proteases is important for its choice of raw material to obtain it. Hence it is not a factor which favors peptide synthesis.
9. An alternative strategy to produce aspartame is kinetically controlled synthesis.
A. True
B. False
Answer: C
Clarification: An alternative strategy to produce aspartame is kinetically controlled synthesis. In this process, the rate of peptide product synthesis (kP) is high as compared to the rate of peptide hydrolysis (kH). This process is ensured by providing an amino acid or peptide which is a more powerful nucleophile than water in accepting a peptide unit from an enzyme-peptide intermediate. Hence the above statement is true.
10. What does the following reaction represent?
A. Hydrogenation
B. Kinetically controlled synthesis
C. Substitution
D. Decomposition
Answer: B
Clarification: The above reaction represents kinetically controlled synthesis. Kinetically controlled synthesis is one wherein the rate of peptide product synthesis (kP) is high compared to that of the rate of peptide hydrolysis (kH). By providing an amino acid or peptide which is a more powerful nucleophile than water in accepting a peptide unit from an enzyme-peptide intermediate, kinetically controlled synthesis may be achieved. In the reaction, X represents an alcohol, amine or other activating group, i.e., the reactant is an ester, amide (peptide) or activated carboxylic acid.
11. The conversion of porcine insulin to human insulin is catalyzed by ________ enzyme.
A. thermolysin
B. trypsin
C. streptokinase
D. asparginase
Answer: B
Clarification: The conversion of porcine insulin to human insulin is catalyzed by trypsin which replaces C-terminal alanine (β30) residue by a threonine. Thermolysin is used to produce aspartame from aspartic acid. Aspartate is produced from aspargine by using asparginase. Plasminogen is converted to plasmin by streptokinase enzyme.
12. The conversion of porcine insulin to human insulin is achieved by ____________ reaction.
A. hydrogenation
B. transpeptidation
C. kinetically controlled synthesis
D. decomposition
Answer: B
Clarification: The conversion of porcine insulin to human insulin is achieved by transpeptidation reaction which replaces C-terminal alanine (β30) residue by a threonine by use of trypsin in an aqueous solution with an organic co-solvent. The protective group can be simply removed later by mild hydrolysis and the product purified by silica gel chromatography.
13. The conversion of porcine insulin to human insulin is achieved by ____________ reaction.
A. hydrogenation
B. transpeptidation
C. kinetically controlled synthesis
D. decomposition
Answer: B
Clarification: The conversion of porcine insulin to human insulin is achieved by transpeptidation reaction which replaces C-terminal alanine (β30) residue by a threonine by use of trypsin in an aqueous solution with an organic co-solvent. The protective group can be simply removed later by mild hydrolysis and the product purified by silica gel chromatography.
14. What is represented in the following diagram?
A. Production of aspartame
B. Production of insulin
C. Production of penicillin
D. Production of glucose syrups
Answer: B
Clarification: Production of insulin from porcine insulin is represented in the diagram. The conversion of to human insulin is done by replacing the C-terminal alanine (β30) residue by a threonine. This is achieved by a single transpeptidation step which is catalyzed by trypsin using a carboxyl-protected threonine in an aqueous solution with an organic co-solvent. Later, the protective group is removed by mild hydrolysis and the product is purified by silica gel chromatography.
