RNA Types
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All Questions for: RNA Types
Question 1: Which type of RNA is most abundant in a cell?
- A rRNA
- B mRNA
- C tRNA
- D snRNA
Explanation: Ribosomal RNA (rRNA) constitutes approximately 80% of total cellular RNA, reflecting its structural and catalytic role in ribosomes.
Question 2: Which RNA type carries genetic information from DNA to ribosomes?
- A mRNA
- B tRNA
- C rRNA
- D miRNA
Explanation: Messenger RNA (mRNA) serves as the intermediary between DNA (in the nucleus) and ribosomes (in the cytoplasm) where protein synthesis occurs.
Question 3: Which RNA type delivers amino acids to the growing polypeptide chain?
- A tRNA
- B mRNA
- C rRNA
- D snRNA
Explanation: Transfer RNA (tRNA) carries specific amino acids to the ribosome, matching its anticodon to the mRNA codon.
Question 4: Which RNA type is the smallest in size?
- A tRNA
- B mRNA
- C rRNA
- D hnRNA
Explanation: tRNA molecules are typically 70–90 nucleotides long — the smallest of the three major classes of RNA. miRNAs are even smaller (~22 nt) but are classified separately as small regulatory RNAs.
Question 5: The cloverleaf-shaped secondary structure is characteristic of:
- A tRNA
- B mRNA
- C rRNA
- D siRNA
Explanation: tRNA folds into a characteristic cloverleaf structure with four stems/loops (D loop, anticodon loop, TΨC loop, variable loop) and further compacts into an L-shape.
Question 6: The three nucleotides on tRNA that pair with the mRNA codon are called the:
- A Anticodon
- B Codon
- C Exon
- D Intron
Explanation: The anticodon is a 3-nucleotide sequence in the anticodon loop of tRNA that base-pairs with the mRNA codon, ensuring the correct amino acid is added.
Question 7: The amino acid attachment site of a tRNA is at its:
- A 3' CCA end
- B 5' phosphate end
- C Anticodon loop
- D D loop
Explanation: The 3' end of tRNA (with the sequence CCA) carries the amino acid, which is attached by an aminoacyl-tRNA synthetase via an ester bond.
Question 8: The enzyme that attaches an amino acid to its specific tRNA is:
- A Aminoacyl-tRNA synthetase
- B Peptidyl transferase
- C RNA polymerase
- D Ribonuclease
Explanation: Aminoacyl-tRNA synthetases activate amino acids (using ATP) and attach them to their cognate tRNAs. Each amino acid has its own specific synthetase.
Question 9: Which tRNA modification is important for its function and stability?
- A Presence of unusual modified bases like pseudouridine
- B Presence of a poly-A tail
- C Presence of a 5' m7G cap
- D Presence of introns in mature form
Explanation: Post-transcriptional modification produces many unusual bases in tRNA, including pseudouridine (Ψ) and dihydrouridine (D), which are essential for folding and codon-anticodon interactions.
Question 10: Ribosomal RNA (rRNA) functions primarily to:
- A Provide structural and catalytic components of ribosomes
- B Carry genetic information from DNA
- C Deliver amino acids to ribosomes
- D Regulate gene expression by degradation of mRNA
Explanation: rRNA is a structural and catalytic component of ribosomes. It helps position mRNA and tRNA, and catalyzes peptide bond formation (peptidyl transferase activity).
Question 11: The catalytic activity of the ribosome (peptidyl transferase) is mediated by:
- A rRNA
- B tRNA
- C mRNA
- D Protein enzymes only
Explanation: The ribosome is a ribozyme — its catalytic activity for peptide bond formation is catalyzed by the 23S rRNA (prokaryotes) or 28S rRNA (eukaryotes), not by a protein enzyme.
Question 12: Which RNA type is found in the nucleolus and helps process pre-rRNA?
- A snoRNA
- B miRNA
- C siRNA
- D piRNA
Explanation: snoRNAs (small nucleolar RNAs) guide chemical modifications (methylation and pseudouridylation) of pre-rRNA in the nucleolus.
Question 13: The spliceosome contains which type of small RNA?
- A snRNA
- B snoRNA
- C miRNA
- D siRNA
Explanation: snRNAs (small nuclear RNAs, e.g., U1, U2, U4, U5, U6) complexed with proteins form snRNPs — the core components of the spliceosome.
Question 14: MicroRNAs (miRNAs) function primarily to:
- A Regulate gene expression by targeting mRNAs for translational repression or degradation
- B Synthesize rRNA in the nucleolus
- C Carry amino acids to ribosomes
- D Form the spliceosome
Explanation: miRNAs are ~22 nt regulatory RNAs that base-pair with target mRNAs to inhibit translation or promote mRNA degradation, thereby controlling gene expression.
Question 15: Small interfering RNAs (siRNAs) differ from miRNAs mainly in that siRNAs:
- A Typically pair with full complementarity to targets and direct cleavage
- B Are longer than miRNAs
- C Are translated into proteins
- D Are found only in bacteria
Explanation: siRNAs are typically derived from exogenous dsRNA or long hairpins and pair fully with their target mRNA to direct its cleavage. miRNAs are encoded in the genome and usually pair only partially with targets.
Question 16: Long non-coding RNAs (lncRNAs) are defined by being:
- A More than 200 nucleotides in length with no protein-coding potential
- B Shorter than 50 nucleotides
- C Translated into small peptides only
- D Found only in mitochondria
Explanation: lncRNAs are >200 nt in length, lack coding potential, and regulate gene expression at transcriptional and post-transcriptional levels (e.g., Xist, HOTAIR).
Question 17: Xist RNA is an example of a lncRNA that functions in:
- A X-chromosome inactivation in female mammals
- B Ribosome assembly
- C tRNA processing
- D Histone mRNA stabilization
Explanation: Xist (X-inactive specific transcript) coats the X chromosome from which it is transcribed and recruits silencing factors, resulting in X-chromosome inactivation in female mammals.
Question 18: Heterogeneous nuclear RNA (hnRNA) is:
- A The primary transcript that becomes mRNA after processing
- B The same as mature mRNA
- C Only found in prokaryotes
- D Encoded by mitochondrial genes only
Explanation: hnRNA refers to the primary RNA polymerase II transcripts in the nucleus, which include both introns and exons and are processed into mature mRNA.
Question 19: The 5S rRNA is transcribed by which polymerase in eukaryotes?
- A RNA polymerase III
- B RNA polymerase I
- C RNA polymerase II
- D RNA polymerase IV
Explanation: Unlike the other rRNAs (transcribed by RNA polymerase I), 5S rRNA is transcribed by RNA polymerase III in the nucleoplasm and then transported to the nucleolus for ribosome assembly.
Question 20: In bacteria, the 16S rRNA is part of which ribosomal subunit?
- A 30S small subunit
- B 50S large subunit
- C 70S whole ribosome only
- D Both subunits equally
Explanation: Bacterial ribosomes (70S) consist of a 30S subunit containing 16S rRNA and a 50S subunit containing 23S and 5S rRNAs. The 16S rRNA plays a key role in mRNA recognition.
Question 21: The Shine-Dalgarno sequence in bacterial mRNA is recognized by:
- A 16S rRNA of the small ribosomal subunit
- B The 5' cap of mRNA
- C tRNA
- D The sigma factor
Explanation: The Shine-Dalgarno (ribosome-binding site) is a purine-rich sequence upstream of the start codon that base-pairs with the anti-SD sequence in 16S rRNA, positioning the ribosome for initiation.
Question 22: Which of the following is NOT a type of RNA?
- A DNA
- B mRNA
- C tRNA
- D rRNA
Explanation: DNA is a distinct nucleic acid. mRNA, tRNA, and rRNA are all types of RNA that function in gene expression.
Question 23: piRNAs (piwi-interacting RNAs) primarily function to:
- A Silence transposons in germ cells
- B Translate mRNA into protein
- C Add poly-A tails to mRNA
- D Form ribosomes
Explanation: piRNAs silence transposons in the germline, protecting genome integrity from mobile genetic element mobilization.
Question 24: Which RNA component of telomerase serves as the template for telomere extension?
- A TERC (telomerase RNA component)
- B mRNA
- C tRNA
- D snRNA
Explanation: Telomerase contains a catalytic reverse transcriptase protein (TERT) and an RNA component (TERC) that provides the template for synthesizing telomeric repeats.
Question 25: The half-life of a typical bacterial mRNA is:
- A A few minutes
- B 24 hours
- C Several days
- D Indefinite (no degradation)
Explanation: Bacterial mRNAs have very short half-lives — typically only a few minutes — allowing rapid responses to changing environmental conditions.