This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Degradation of mRNA”.
1. Nonstop mediated decay is observed mostly in ____________
a) Bacteria
b) Fungi
c) Protozoa
d) Animal
View Answer
Explanation: Nonstop mediated decay rescues ribosomes that translate mRNAs that lack a stop codon. Eukaryotic mRNAs, due to tailing, terminate with a poly-A tail. When mRNA lacking a stop codon is translated it translates through the poly-A tail. This results in the addition of multiple lysines to the end of the protein thus stalling the ribosome at the end of the mRNA and thus triggering nonstop mediated decay.
2. Ski7 is known to recruit ____________ enzyme for mRNA degradation.
a) Endonuclease
b) 3’→5’ exonuclease
c) 5’→3’ exonuclease
d) Nuclease
View Answer
Explanation: The protein Ski7 is related to the class II release factor eRF3, and stimulates the dissociation of the ribosome bound to the mRNA without a stop codon. Thus, Ski7 recruits the 3’→5’ exonuclease to the damaged mRNA for mRNA degradation.
3. Translation of an mRNA is the only way to proofread mRNAs.
a) True
b) False
View Answer
Explanation: In the absence of translation, the damaged mRNA is not rapidly degraded and has normal stability. Thus eukaryotic cells rely on the translation mechanism to proofread their mRNA.
4. Introns makes up about ____________ % of the total mRNA.
a) 50
b) 70
c) 90
d) 80
View Answer
Explanation: Over about 90% of the total pre-mRNA sequence are introns. These intronic sequences are degraded within the nucleus after they have been excised from the mRNA.
5. The enzyme that degrades the mRNA recognizes ____________ bond of mRNA.
a) 2’ – 5’
b) 2’ – 3’
c) 2’ – 5’
d) 3’ – 5’
View Answer
Explanation: The enzyme that degrades the mRNA recognizes three specific sites in the intronic mRNA. These are the unique 2’ – 5’ bond formed at the branching point as well as the 3’ and 5’ ends of the RNA molecule.
6. The introns are degraded due to ____________
a) Specific enzymatic sequence
b) Unprotected ends
c) Lariat formation
d) Endonuclease activity
View Answer
Explanation: The ends of the processed mRNA are protected from degradation by capping and tailing. In case of the bare ends of the introns, it is easily identified by 3’ or 5’ exonucleases and is thus degraded.
7. How many ways of RNA degradation are found in eukaryotic cell?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Two ways of RNA degradation are found in eukaryotic cell. They are nonsense mediated mRNA decay where mRNA with premature stop codon and/or incomplete open reading frame is degraded. And secondly, nonstop mediated decay rescues ribosomes that translate mRNAs that lack a stop codon.
8. Nonsense mediated mRNA decay is proceeded due to the ____________
a) Absence of tailing
b) Absence of capping
c) Absence of stop codon
d) Absence of ORF
View Answer
Explanation: Nonsense mediated mRNA decay is proceeded due to two triggering factors as a quality control system. These two factors are:
i. Absence of open-reading frame (ORF)
ii. Presence of premature termination codon.
9. Presence of premature stop codon triggers nonstop mediated decay.
a) True
b) False
View Answer
Explanation: Nonsense mediated decay is triggered when ribosomes encounter premature termination/stop codon. These premature stop codons are identified when they occurs more than 50 nucleotides upstream of an exon-exon junction in the spliced mRNA.
10. Which of the following types of RNA is the most stable?
a) mRNA
b) hnRNA
c) tRNA
d) snRNA
View Answer
Explanation: Only two types of RNA are most stable in the cell and are rRNA and tRNA. This ability largely accounts for the high levels of these RNAs in both prokaryotic and eukaryotic cells.
11. Which of the following is not a step to degrade mRNA?
a) Deadenylation
b) 5’→3’ exonuclease activity
c) 3’→5’ exonuclease activity
d) Site-specific degradation
View Answer
Explanation: The steps to degrade mRNA are as follows:
i. Deadenylation that is, shortening of the poly-A tail, for the degradation from the 3’ end by 3’→5’ exonuclease
ii. Removal of 5’ cap for degradation from the 5’ end by 5’→3’ exonuclease.
12. The shorter half life of mRNAs is essential for the cells environmental adaptation in prokaryotes.
a) True
b) False
View Answer
Explanation: Bacterial mRNAs are rapidly degraded and usually have half-lives of only 2 to 3 minutes. This rapid turnover of bacterial mRNAs allows the cell to respond quickly to alterations in its environment, such as changes in the availability of nutrients require for growth.
13. The half life of mRNA of both prokaryotic and eukaryotic cells is same.
a) True
b) False
View Answer
Explanation: Bacterial mRNAs are rapidly degraded and usually have half-lives of only 2 to 3 minutes. Instead the mRNAs of eukaryotic cells have a half life ranging from 30 minutes to approximately 20 hours.
14. mRNA for which of the following has a longer half life?
a) SSB protein
b) Polymerase
c) G protein
d) Nucleases
View Answer
Explanation: The unstable mRNAs generally code for regulatory proteins, such as transcription factors, whose level within the cell vary rapidly in response to the environmental stimuli. In contrast, mRNAs encoding structural proteins, such as G protein, or central metabolic enzymes, such as kinases, generally have long half lives.
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