Cytogenetics Multiple Choice Questions on “TRNA”.
1. In eukaryotes tRNA are transcribed by ________
A. RNA polymerase I
B. RNA polymerase II
C. RNA polymerase III
D. RNA polymerase IV
Answer: C
Clarification: The RNA polymerase III transcribes the tRNA in eukaryotes while in prokaryotes there is only one RNA polymerase for all type of RNA.
2. The tertiary structure of the tRNA is __________
A. Clover leaf
B. Crossbow
C. L shaped
D. Plus shaped
Answer: C
Clarification: The tertiary structure of the tRNA is L shaped while the secondary structure is cloverleaf shaped. The tRNA has three stem loop structures.
3. Which one of this is not a normal base found in tRNA?
A. Pseudo uridine
B. Thimidine
C. I base
D. OxoG base
Answer: D
Clarification: Unlike most RNA tRNA has some special bases like pseudo uridine, dihydroxy uridine etc. But oxoG is a base produced due to oxidative damage, it is not normally found in RNA.
4. What is the amino acid binding sequence in tRNA?
A. AUG
B. GGU
C. CCA
D. T ψ C
Answer: C
Clarification: The CCA sequence of the aminoacyl arm of tRNA is responsible for binding the amino acid. While AUG is a start codon and T ψ C is another arm of the tRNA.
5. Which arm of the tRNA can act as a structural recognition feature?
A. Anticodon
B. Dihydroxyuridine arm
C. T phi C arm
D. Variable arm
Answer: D
Clarification: The variable arm, as its name suggest, differs for different tRA. Some amino acyltRNA synthetase can use them as recognition feature.
6. Class II amino acyl tRNA synthetase transfers the amino acids to the tRNA __________
A. 3’-OH of the A base
B. 3’-OH of the C base
C. 2‘-OH of the A base
D. 2’-OH of the C base
Answer: C
Clarification: Class II aminoacyl tRNA synthetase transfers the amino acid to the 2’-OH of the tRNA. There is a quick equilibrium between the 2’ and the 3’-OH. On the other hand class I amino acyl tRNA synthetase transfers it to the 3’-OH.
7. Which of the following tRNA is charged by class II aminoacyl tRNA synthetase?
A. Glu
B. Asp
C. Ser
D. Met
Answer: B
Clarification: Asp is charged by class II amino acyl tRNA synthetase. It recognized the structural features and not the anticodon loop, there is also no bending of the 3’-OH end of the amino acyl arm.
8. In an experiment you charge a tRNA with a wrong base. You allow the mixture to stand for a while. What will you expect to see?
A. Properly charged tRNA
B. Mischarged tRNA
C. Uncharged tRNA
D. Degraded tRNA
Answer: C
Clarification: Certain synthetases can cleave the bond between wrong amino acid and the tRNA. This is a type of proofreading mechanism that ensures correct amino acid incorporation.
9. Proofreading activity existing universally in synthetase as a double sieve mechanism.
A. True
B. False
Answer: B
Clarification: Only the synthetase where there is very less structural discrimination or difference in binding energies this mechanism is present. Where there is no doubt proofreading is unnecessary.
10. What is the amino acid present in the binding pocket of glutaminyl amino acyl tRNA synthetase?
A. Asp
B. Lys
C. Arg
D. Gln
Answer: D
Clarification: The 3’-OH of the aminoacyl arm of the tRNA enters the binding pocket of the synthetase to interact with a Gln amino acid correctly placed. This is used to distinguish it from Asp and Asn.
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