Engineering Tyrosyl-tRNA Synthetase - Protein Engineering Applications Questions and Answers

This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Applications – Engineering Tyrosyl-tRNA Synthetase”.

1. Which of the following enzyme catalyzes the charging of tRNA^Tyr with tyrosine?
a) Tyrosine synthetase
b) RNA activating enzyme
c) Tyrosyl-tRNA synthase
d) Tyrosyl-tRNA synthetase
View Answer

Answer: d
Explanation: Tyrosyl-tRNA synthetase catalyzes the charging of tRNA^Tyr with tyrosine. It is a two-stage reaction in which the tyrosine is first activated at its carboxyl group with ATP to form tyrosyl adenylate. Tyrosine synthetase, RNA activating enzyme, or Tyrosyl-tRNA synthase do not catalyze the charging of tRNA^Tyr with tyrosine.

2. The C-terminal domain of tyrosyl-tRNA synthetase contains major binding determinants for the tRNA.
a) False
b) True
View Answer

Answer: b
Explanation: The above statement is true. The C-terminal domain of tyrosyl-tRNA synthetase contains major binding determinants for the tRNA. The C-terminal domain was excised at the level of the cloned gene and the kinetics of the N-terminal domain was assayed. The kinetics of the tyrosine activation were identical for the wild type and the truncated enzyme, but the truncated enzyme did not charge or bind tRNA.

3. Which of the following shaped structure is formed by the tRNA^Tyr ?
a) J-shaped
b) O-shaped
c) I-shaped
d) L-shaped
View Answer

Answer: d
Explanation: tRNA^Tyr folds into an L-shaped structure, with the receptor stem and the TψC stem forming one arm, and the anticodon stem and extra loop the other arm. tRNA^Tyr does not form J-shaped, O-shaped, or I-shaped.

4. In tRNA charging, the K_m (ATP) is unaffected in the heterodimer, but the K_cat is one half that of wild type enzyme.
a) False
b) True
View Answer

Answer: b
Explanation: The above statement is true. The C-terminal domain of tyrosyl-tRNA synthetase contains major binding determinants for the tRNA. Thus, the heterodimer appears to be a fully refolded, active molecule, in which one subunit can complement a lesion on the other subunit.

5. Which of the following amino acids can be used in place of lysine, arginine, and histidine to remove the electrostatic charge but retain the hydrophilic nature of the side chain?
a) Aspartic acid and glutamic acid
b) Aspartic acid and glutamine
c) Asparagine and glutamic acid
d) Asparagine and glutamine
View Answer

Answer: d
Explanation: Asparagine and glutamine can be used in place of lysine, arginine, and histidine to remove the electrostatic charge but retain the hydrophilic nature of the side chain. Aspartic acid and glutamic acid cannot be used in place of lysine, arginine, and histidine to remove the electrostatic charge and retain the hydrophilic nature of the side chain. Asparagine and glutamine contain neutral but polar side chains.

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6. The charging of tRNA^Tyr with tyrosine is a single-stage reaction.
a) True
b) False
View Answer

Answer: b
Explanation: The above statement is false. The charging of tRNA^Tyr with tyrosine is a two-stage reaction. The tyrosine is first activated at its carboxyl group with ATP to form tyrosyl adenylate. Subsequently, the adenylate is attacked by the 2’ or 3’ hydroxyl of the tRNA to give tyrosyl-tRNA^Tyr.

7. Tyrosine is activated at an amino group with ATP to form tyrosyl adenylate.
a) True
b) False
View Answer

Answer: b
Explanation: The above statement is false. Tyrosine is activated at the carboxyl group with ATP to form tyrosyl adenylate. The tyrosyl-tRNA synthetase catalyzes the charging of tRNA^Tyr with tyrosine. Each amino acid has its specific tRNA to which it binds.

8. The tRNA makes contact with the synthetase at only a single specific position.
a) True
b) False
View Answer

Answer: b
Explanation: The above statement is false. The tRNA makes contact with the synthetase over a wide region, and in particular at both the acceptor arm and anticodon stem and loop. Hence, the tRNA does not make contact with the synthetase at only a single specific position.

9. Both the subunits of heterodimers are involved in tRNA binding.
a) False
b) True
View Answer

Answer: b
Explanation: The above statement is true. Both the subunits of heterodimers are involved in tRNA binding. The heterodimer is a fully refolded, active molecule, in which one subunit can complement a lesion on the other subunit.

10. Which of the following enzyme catalyzes the chemical reaction shown in the figure below?

a) DNA ligase
b) Tyrosyl mRNA synthetase
c) Tyrosine ligase
d) Tyrosyl-tRNA synthetase
View Answer

Answer: d
Explanation: The chemical reaction shown in the figure above is catalyzed by tyrosyl-tRNA synthetase. Tyrosyl-tRNA synthetase is also known as tyrosine-tRNA ligase. It is not catalyzed by DNA ligase, tyrosyl mRNA synthetase, or tyrosine ligase.

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