Cytogenetics Multiple Choice Questions on “RNA Processing Control”.
1. If you run the whole RNA extract on a gel you will get ____________ bands normally.
A. Many
B. One
C. Two
D. Three
Answer: C
Clarification: In running a whole RNA extract you will get 2 bands each corresponding to 60S rRNA and 40S rRNA for eukaryotes and corresponding 30S and 50S for prokaryotes.
2. tRNA constitutes ___________ % of all RNA.
A. 85
B. 25
C. 15
D. <5
Answer: C
Clarification: tRNA constitutes only 15% of the entire RNA. Major portion of 5& is the rRNA while very small portion is the mRNA.
3. The pre-rRNA transcript transcribed by the RNA pol Idoesn’t include_________
A. 18S
B. 5S
C. 5.8S
D. 28S
Answer: B
Clarification: White the 18S, 5.8 S and the 28S subunits are present in the pre rRNA transcript, the 5S subunit comes from another region that is transcribed by the RNA pol III.
4. The primary transcript is ______________
A. 52S
B. 45S
C. 32S
D. 17S
Answer: B
Clarification: The pre-rRNA transcript made by the RNA pol I is 45S, it is cleaved to give the 28S, 18S and 5.8S subunits of the ribosomal RNA.
5. The cleavage of the rRNA is aided by the snRNA.
A. True
B. False
Answer: B
Clarification: The snRNA helps in the splicing of mRNA, however the cleavage of the rRNA is done via the small nucleolar restricted RNA or snoRNAs instead.
6. Which of the following is not a normal modification of the rRNA primary transcript?
A. Conversion of U base to Pseudo uridine
B. Methylation of the 2’- OH region of specific rRNA bases
C. Cleavage of the intervening regions by exonucleases
D. Proteins modulating the cleavage
Answer: D
Clarification: In case of rRNA the snoRNA along with proteins making snoRNP aids in cleavage and modifications, and not just proteins as seen in case of tRNA primary transcript.
7. Bacterial pre rRNA transcript has ________________
A. 23S 4S 16S 5S
B. 16S 4S 23S 5S
C. 16S 5S 23S
D. 23S 16S 5S
Answer: B
Clarification: The pre-rRNA transcript of prokaryotes is 30S, it has 16S 4S 23S and 5S subunits in sequence where the 4S subunit codes for the tRNA.
8. Which one of the following characters doesn’t go along with tRNA?
A. Its primary transcript is processed by proteins
B. The cleavage at the 5’ and 3’ end of the intron is simultaneous
C. The introns are seen in yeast and they are larger than exons
D. ATP and GTP hydrolysis joins the two RNA halves at the two ends of the introns
Answer: C
Clarification: It is true that the intron is seen in the yeast tRNA primary transcript. But it is very short about 14bp and the introns in tRNA are generally much shorter than the mRNA.
9. The 5’ end of the tRNA transcript is cleaved by____________
A. RNase K
B. Exonuclease VII
C. Endonucleace I
D. Rnase P
Answer: D
Clarification: RNase P removes the 5’ nucleotide sequence or the tRNA transcript. This generates a 5’ end that is shorter than the 3’ end.
10. Which of the following is not a normal processing step of the tRNA?
A. The 3’ end U is replaced by CCA
B. The Purines are methylated and isopentyl groups are transferred to them
C. The 3’ OH is methylated
D. U bases at specific sites are converted to pseudo uridine, ribo thimidine or dihydrouridine