This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Gene Expression – Ribosomal RNA and tRNA”.
1. In a mammalian cell, which is the most abundant type of RNA?
a) rRNA
b) mRNA
c) siRNA
d) tRNA
View Answer
Explanation: Ribosomal RNA (called rRNA) is the most abundant type of RNA in a cell. More than 80 percent of the RNA in a cell consists of ribosomal RNA. Other types of RNAs are transfer RNA and messenger RNA among others.
2. The human genome consists of _____ rDNA.
a) 2
b) 4
c) 5
d) 7
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Explanation: The human genome has five different clusters of ribosomal DNA, each on a different chromosome. Ribosomal DNA is the part of DNA that codes for ribosomal RNA, the most abundance type of RNA in a cell.
3. Aggregated clusters of rDNA in a cell are called _______________
a) nucleoli
b) chromatin
c) chromosome
d) ribosome
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Explanation: In a non-dividing cell (the cell which is in interphase), the clusters of rDNA come together to form irregularly shaped nuclear structures called nucleolus (plural nucleoli). The nucleoli are dense with primary RNA transcripts.
4. Which of the following are ideal subjects for the study of rRNA synthesis and processing?
a) spermatocytes
b) mitochondria
c) oocytes
d) amphibians
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Explanation: Oocytes are the ideal candidates for the study of rRNA synthesis and processing. Amplification of rDNA is required by the fertilized egg to begin embryonic development; therefore oocytes contain hundreds of nucleoli that actively manufacture ribosomal RNA.
5. Nontranscribed spacer is not transcribed.
a) True
b) False
View Answer
Explanation: Nontranscribed spacer is that region of the ribosomal gene cluster that is not transcribed into RNA. Transcription is the first step in genetic expression and regulation.
6. How many types of distinct ribosomal RNAs are present in eukaryotic ribosomes?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Eukaryotic ribosome or the 80S ribosome is made up of 2 unequal subunits(40S and 60S). The 40S subunit contains a 18S rRNA and the 60S subunit contains the 28S, 5S and the 5.8S rRNAs. Therefore the eukaryotic ribosomes have 4 rRNAs.
7. How many post-translational modifications occur in the pre-rRNA (primary transcript)?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Two types of post-translational modifications are characteristic of pre-rRNA, large number of methylated nucleotides and pseudouridine residues. These make the pre-rRNA peculiar and contrasting from other primary RNA transcripts.
8. Which of the following is a pre-rRNA?
a) 5S
b) 5.8S
c) 45S
d) 18S
View Answer
Explanation: The 45S RNA molecule is a pre-rRNA, of length 13,000 nucleotides. It is cleaved into 18S, 5.8S and 28S mature rRNA. Most of the pre- rRNA is spliced and reduced in length before turning into mature rRNA.
9. The processing of pre-rRNA is done using __________
a) nucleolus
b) mRNA
c) snoRNA
d) siRNA
View Answer
Explanation: The processing of pre- rRNA is done using the small nucleolar RNAs (called snoRNA) along with some proteins. Processing of pre- rRNA includes removal of non-coding sequences and posttranscriptional modifications.
10. 5S rRNA is present only in eukaryotes.
a) True
b) False
View Answer
Explanation: 5s rRNA is present as part of the large ribosomal subunit in both eukaryotic and prokaryotic organisms. Unlike other types of rRNA, 5S rRNA is transcribed from a separate primary transcript.
11. Which among the following have the largest number of tRNA genes?
a) humans
b) bacteria
c) yeast
d) fruit flies
View Answer
Explanation: Transfer RNAs (called tRNAs) play an important role in peptide synthesis. Humans contain about 1300 tRNA genes greater than other organisms mentioned. Bacteria has least number of tRNA genes.
12. Transfer RNAs (tRNA) are transcribed by _________________
a) pre-RNA
b) rDNA
c) tDNA
d) siRNA
View Answer
Explanation: Clusters of tDNA located within the genome are responsible for the transcription of transfer RNAs. Transfer RNAs primarily function in the translation of proteins.
13. Ribonuclease P is involve in the processing of ___________________
a) sno RNA
b) rRNA
c) pre-tRNA
d) pre-mRNA
View Answer
Explanation: Ribobuclease P is an endonuclease present both in eukaryotes and prokaryotes. It is involved in the processing of pre-tRNA. Transfer RNA is synthesized from the processed primary transcript.
Sanfoundry Global Education & Learning Series – Cell Biology.
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