1. What are microRNAs (miRNAs)?
A. Proteins involved in DNA replication
B. Small non-coding RNAs that regulate gene expression
C. Ribosomal RNAs involved in translation
D. Messenger RNAs that encode proteins
Answer: B
Explanation: MicroRNAs are small non-coding RNAs, typically 20-24 nucleotides long, that regulate gene expression at the post-transcriptional level by binding to complementary sequences on target mRNAs, leading to their degradation or translational repression.
2. Where are miRNAs primarily synthesized?
A. Endoplasmic reticulum
B. Mitochondria
C. Nucleus
D. Cytoplasm
Answer: C
Explanation: miRNAs are transcribed as primary miRNAs (pri-miRNAs) in the nucleus by RNA polymerase II or III. They are then processed into precursor miRNAs (pre-miRNAs) before being exported to the cytoplasm.
3. Which enzyme processes pri-miRNAs into pre-miRNAs?
A. Dicer
B. Drosha
C. Argonaute
D. RNase H
Answer: B
Explanation: Drosha, a nuclear RNase III enzyme, processes pri-miRNAs into ~70-nucleotide pre-miRNAs, which are then transported to the cytoplasm.
4. Which protein is involved in cleaving pre-miRNAs into mature miRNAs?
A. Drosha
B. Dicer
C. Exportin-5
D. Argonaute
Answer: B
Explanation: Dicer, a cytoplasmic RNase III enzyme, cleaves pre-miRNAs into mature double-stranded miRNA duplexes.
5. What is the role of the Argonaute protein in miRNA function?
A. DNA replication
B. Cleaving miRNAs
C. Incorporating miRNAs into the RNA-induced silencing complex (RISC)
D. Exporting miRNAs
Answer: C
Explanation: Argonaute proteins are core components of RISC. They bind mature miRNAs and guide them to target mRNAs for silencing.
6. Which cellular process is regulated by miRNAs?
A. DNA replication
B. Transcription
C. Post-transcriptional gene expression
D. Protein folding
Answer: C
Explanation: miRNAs regulate gene expression at the post-transcriptional level by targeting mRNAs, leading to their degradation or translational repression.
7. How do miRNAs recognize their target mRNAs?
A. Through base pairing with the promoter
B. By binding ribosomes
C. Through sequence complementarity to the 3′ untranslated region (3′ UTR) of mRNAs
D. By interacting with DNA polymerase
Answer: C
Explanation: miRNAs bind to complementary sequences in the 3′ UTR of target mRNAs, guiding the RISC to mediate mRNA degradation or translational inhibition.
8. What is the seed region in miRNAs?
A. The coding sequence of the target gene
B. A 7-8 nucleotide region crucial for target recognition
C. The entire length of the miRNA
D. The region that binds the ribosome
Answer: B
Explanation: The seed region is a conserved 7-8 nucleotide sequence at the 5′ end of the miRNA critical for binding and recognizing complementary target mRNA sequences.
9. What is the effect of miRNAs on gene expression?
A. Always upregulation
B. Always downregulation
C. Either upregulation or downregulation depending on the target
D. No effect
Answer: B
Explanation: miRNAs typically downregulate gene expression by either degrading target mRNAs or inhibiting their translation.
10. Which cellular pathway is miRNA dysregulation often associated with?
A. Apoptosis
B. Cancer
C. Neurodegeneration
D. All of the above
Answer: D
Explanation: miRNA dysregulation is linked to various diseases, including cancer, neurodegenerative disorders, and disrupted apoptotic pathways.
11. How are miRNAs exported from the nucleus to the cytoplasm?
A. By passive diffusion
B. By Exportin-5
C. Through nuclear pores without assistance
D. By Argonaute proteins
Answer: B
Explanation: Exportin-5, a nuclear export protein, transports pre-miRNAs from the nucleus to the cytoplasm.
12. Which molecule is typically used as a template for miRNA transcription?
A. RNA
B. DNA
C. Protein
D. Lipid
Answer: B
Explanation: miRNAs are transcribed from DNA as primary transcripts by RNA polymerase II or III.
13. What is the primary outcome of miRNA binding to mRNAs?
A. Increased translation
B. mRNA stabilization
C. mRNA degradation or translational repression
D. Formation of double-stranded RNA
Answer: C
Explanation: miRNA binding to mRNAs results in either their degradation or translational repression, depending on the extent of sequence complementarity.
14. Which of the following diseases has been directly linked to miRNA dysregulation?
A. Diabetes
B. Cardiovascular diseases
C. Cancer
D. All of the above
Answer: D
Explanation: Aberrant miRNA expression has been implicated in various diseases, including diabetes, cardiovascular conditions, and cancer.
15. What is the role of miRNAs in cancer?
A. Only act as tumor suppressors
B. Only act as oncogenes
C. Can act as both tumor suppressors and oncogenes
D. Do not play any role in cancer
Answer: C
Explanation: miRNAs can function as tumor suppressors by downregulating oncogenes or as oncogenes by inhibiting tumor suppressor genes.
