This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “RNAs in Gene Regulation”.
1. siRNA are produced by __________
a) Transcription
b) DNA damage
c) RNA damage
d) Enzymatic action
View Answer
Explanation: siRNA or short interfering RNAs are enzymes involved in the process of RNA interference. They are generally generated by the action of certain enzymatic activities such as dicer.
2. Which of the following is not the handiwork of siRNA?
a) Translational inhibition
b) mRNA destruction
c) Base dimerization
d) Promoter silencing
View Answer
Explanation: siRNA causes gene silencing in three pathways. They operate through translational inhibition, mRNA degradation and promoter silencing. Base dimerization is caused by DNA exposure to UV rays causing errors during replication.
3. Introduction of ds DNA can repress gene expression.
a) True
b) False
View Answer
Explanation: The discovery that simply introducing a double stranded RNA into a cell can repress the gene containing sequencings identical to that dsRNA. This phenomenon was first reported in 1998 found by the experiment in the worm C. elegans.
4. Dicer is __________
a) DNAse-like enzyme
b) RNAse-like enzyme
c) An endonuclease
d) An exonuclease
View Answer
Explanation: Dicer is an RNAse III-like enzyme that recognizes and digests long double stranded RNAs. The products of this are short double-stranded fragments about 23 nucleotides long.
5. Which of the following pathways involve the Dicer for gene silencing?
a) Chromatin modification
b) Structural gene triple helix formation
c) DNA polymerase binding
d) RNA polymerase binding
View Answer
Explanation: Dicer is involved in the production of siRNA that inhibits the expression of homologous genes in three ways. They are translational inhibition, mRNA degradation and promoter silencing by remodeling of chromatin.
6. The RNAi mediated gene silencing includes the binding of siRNA to form a complex with the target gene called RISC.
a) True
b) False
View Answer
Explanation: RISC or RNA induced silencing complex is machinery that includes the siRNA themselves, various proteins including members of the Argonaut family. The RNAi mediated gene silencing includes the binding of siRNA to form a complex with proteins to form the RISC.
7. The RNAi mediated gene silencing is an ATP-dependent procedure.
a) True
b) False
View Answer
Explanation: Once the RISC complex is formed with the double-stranded siRNA it is denatured in an ATP-dependent manner. The appearance of the single stranded RNA activates the RISC complex.
8. If the siRNA is a complete homolog of the target mRNA sequences what is the net result?
a) Double helix formation
b) Translation inhibition
c) Chromatin modification
d) mRNA degradation
View Answer
Explanation: If the siRNA is a complete homolog of the target mRNA sequence the latter is seen to be degraded. In case is there is not complete complementation the inhibition of translation takes place. A nuclease is responsible for the degradation in case of complete complementation.
9. Binding of siRNA to the DNA does not lead to __________
a) Chromatin remodeling
b) Promoter unavailability
c) Transcriptional inhibition
d) Triple helix formation
View Answer
Explanation: The RISC complex can also be directed by a siRNA into the nucleus where it associates with the complementary region of the DNA. Once there the complex recruits the other proteins that modify the structure around the promoter of the gene thus inhibiting transcription.
10. Which of the following RNAs can induce gene silencing?
a) miRNA
b) snoRNA
c) ssRNA
d) ncRNA
View Answer
Explanation: Apart from siRNA, miRNA and piRNA causes gene silencing. The miRNAs or microRNAs are naturally occurring RNAs that direct the repression of genes, but mostly in plants and worms.
11. The miRNAs are transcribed from non-protein encoding genes and are typically __________ nucleotides long.
a) 10 – 15
b) 12 – 15
c) 18 – 20
d) 20 – 25
View Answer
Explanation: miRNA or microRNAs are small, non-coding RNA molecules encoded in the genome of plants, animals and their viruses. These are highly conserved sequences ranging about 20 – 25 nucleotides that appear to regulate post-transcriptional gene regulation.
12. The first miRNA was identified in C. elegans named __________
a) Lin-2
b) RISC
c) Lin-4
d) DICER
View Answer
Explanation: The first miRNA was first identified by Victor Ambros and colleagues in C. elegans named Lin-4. The Lin-4 gene was unusual as it did not encoded a protein but rather a small RNA that imperfectly base-pairs with the complementary sequences on the target mRNAs in order to block gene expression. The lin-4 gene controls the expression of the lin-14 gene.
13. Pick the odd one out.
a) siRNA
b) snoRNA
c) piRNA
d) miRNA
View Answer
Explanation: siRNA, piRNA and miRNA can all mediate regulation of expression of the gene by the process of gene silencing and RNA interference. snoRNA does not mediate gene regulation by RNA interference.
14. Inactive miRNA undergoes how many cleavages before incorporation into the RISC complex?
a) 0
b) 1
c) 2
d) 3
View Answer
Explanation: The process of formation of the active RNA complex needs the cleavage miRNA. The miRNA gene is transcribed into pri-miRNA that folds into a hairpin structure. Nuclear enzyme Drosha cleaves pri-miRNA into pre-miRNA which is exported out from the nucleus. In the cytosol dicer cleaves the pre-miRNA into miRNA. This miRNA is now incorporated into RISC.
15. piRNAs are synthesized in a Dicer dependent mechanism.
a) True
b) False
View Answer
Explanation: piRNAs or Piwi-interacting RNAs are the most recently discovered class of longer small RNAs of about 25-30 nucleotides. This piRNA binds to the Piwi clade of argonaute proteins. These are thought to be derived from ssRNA precursors and are produced without the dicer cleavage step and thus are dicer-independent.
16. Stem loop precursors are generally seen in which of the following?
a) siRNA
b) miRNA
c) piRNA
d) Both siRNA and miRNA
View Answer
Explanation: miRNAs are processed from stem-loop precursors with incomplete double-stranded character. siRNAs are derived from a long, fully complementary double stranded RNAs. piRNAs are derived from long ssRNA precursors and does not contain stem-loop structures.
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