RNA Processing
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All Questions for: RNA Processing
Question 1: In eukaryotes, RNA processing of pre-mRNA occurs primarily in the:
- A Nucleus
- B Cytoplasm
- C Mitochondria
- D Ribosome
Explanation: Pre-mRNA is processed in the nucleus before export to the cytoplasm. Processing includes 5' capping, splicing, and 3' polyadenylation.
Question 2: Which of the following is NOT a step in eukaryotic pre-mRNA processing?
- A Translation of the mRNA
- B 5' capping
- C Intron splicing
- D 3' polyadenylation
Explanation: Pre-mRNA processing involves 5' capping, intron splicing, and 3' polyadenylation. Translation occurs later in the cytoplasm and is not part of RNA processing.
Question 3: The 5' cap of eukaryotic mRNA consists of:
- A 7-methylguanosine linked by a 5'-5' triphosphate bond
- B A chain of ~200 adenine residues
- C A short RNA primer
- D A methylated cytosine residue
Explanation: The 5' cap is a 7-methylguanosine (m7G) residue attached to the first nucleotide of the mRNA via an unusual 5'-5' triphosphate linkage.
Question 4: The primary function of the 5' cap is to:
- A Protect mRNA from degradation and aid in translation initiation
- B Encode the start codon
- C Provide the poly-A tail attachment site
- D Direct splicing of the first intron
Explanation: The 5' cap protects mRNA from 5'→3' exonucleases, aids in mRNA export from the nucleus, and serves as a recognition signal for ribosome binding during translation.
Question 5: The poly-A tail is added to the 3' end of eukaryotic mRNA by:
- A Poly-A polymerase (PAP)
- B RNA polymerase II
- C Primase
- D Spliceosome
Explanation: After cleavage at the polyadenylation signal (AAUAAA), poly-A polymerase (PAP) adds ~150–250 adenine residues to the 3' end without a template.
Question 6: The consensus polyadenylation signal in eukaryotic pre-mRNA is:
- A AAUAAA
- B GGGCGG
- C TATAAT
- D CCAATCA
Explanation: The hexanucleotide AAUAAA (in RNA) is the highly conserved polyadenylation signal that directs cleavage and poly-A addition.
Question 7: The poly-A tail of mRNA primarily functions to:
- A Increase mRNA stability and translation efficiency
- B Encode amino acids at the C-terminus
- C Provide the 5' cap structure
- D Direct the mRNA to the mitochondria
Explanation: The poly-A tail protects mRNA from 3'→5' exonucleases, enhances translation efficiency, and helps in mRNA export from the nucleus.
Question 8: Introns are removed from pre-mRNA by a process called:
- A Splicing
- B Capping
- C Polyadenylation
- D Editing
Explanation: Splicing removes introns and joins exons to produce mature mRNA. The reaction is catalyzed by the spliceosome.
Question 9: The spliceosome is composed of:
- A snRNAs and associated proteins
- B rRNAs only
- C DNA and histones
- D Only protein enzymes
Explanation: The spliceosome consists of five snRNPs (U1, U2, U4, U5, U6), each containing an snRNA and associated proteins, plus numerous additional protein factors.
Question 10: The 5' splice site consensus sequence in pre-mRNA is:
- A GU
- B AG
- C AU
- D CC
Explanation: The 5' splice site (donor) has the consensus GU, and the 3' splice site (acceptor) has AG — hence the 'GU-AG rule' for splice site recognition.
Question 11: The 3' splice site consensus sequence in pre-mRNA is:
- A AG
- B GU
- C AU
- D GG
Explanation: The 3' splice site (acceptor) is characterized by the dinucleotide AG, which is preceded by a polypyrimidine tract.
Question 12: The branch point adenosine residue in pre-mRNA splicing is critical for:
- A Formation of the lariat intermediate in the first transesterification
- B Adding the 5' cap
- C Terminating transcription
- D Adding the poly-A tail
Explanation: The branch point adenosine, typically ~20–50 nt upstream of the 3' splice site, serves as the nucleophile in the first transesterification reaction, forming the lariat intermediate.
Question 13: Alternative splicing allows:
- A Production of multiple proteins from a single gene
- B Production of multiple genes from one protein
- C Reversal of transcription
- D Removal of the 5' cap
Explanation: Alternative splicing generates multiple mRNA variants from a single gene by varying which exons are included, greatly expanding proteome diversity from a limited number of genes.
Question 14: Approximately what percentage of human genes undergo alternative splicing?
- A More than 90%
- B About 10%
- C About 25%
- D Less than 5%
Explanation: Over 90% of human multi-exon genes undergo alternative splicing, greatly increasing proteome diversity — a major factor in the complexity of the human proteome.
Question 15: RNA editing is:
- A A post-transcriptional change in RNA sequence that differs from the DNA template
- B Another name for splicing
- C Addition of the 5' cap
- D The same as polyadenylation
Explanation: RNA editing changes the nucleotide sequence of an RNA after transcription, allowing the sequence to differ from the genomic template. Two main types are C→U and A→I editing.
Question 16: Apolipoprotein B (ApoB) mRNA undergoes tissue-specific RNA editing in the intestine by:
- A A C→U edit creating a premature stop codon
- B A U→C edit
- C A large deletion
- D Alternative splicing
Explanation: In the intestine, a C→U RNA editing event creates a premature stop codon, generating ApoB-48 (shorter). In the liver, the unedited mRNA produces ApoB-100 (longer).
Question 17: The enzyme adenosine deaminase acting on RNA (ADAR) catalyzes:
- A Adenosine → inosine (A→I) editing
- B Cytosine → uracil editing
- C Guanine → adenine editing
- D Uracil → thymine editing
Explanation: ADAR enzymes convert adenosine to inosine (A→I) in RNA. Since inosine is read as guanosine by the translation machinery, this can change codon meaning.
Question 18: Mature mRNA is exported from the nucleus to the cytoplasm through:
- A Nuclear pore complexes
- B The endoplasmic reticulum
- C Gap junctions
- D The Golgi apparatus
Explanation: Nuclear pore complexes (NPCs) mediate transport of mature mRNA and other RNAs across the nuclear envelope in an energy-dependent manner.
Question 19: tRNA and rRNA undergo extensive post-transcriptional processing, including:
- A Cleavage and base modifications
- B 5' capping and polyadenylation
- C Reverse transcription
- D Addition of histones
Explanation: tRNAs and rRNAs undergo cleavage from longer precursors, base modification (methylation, pseudouridylation), and for tRNA, addition of the 3' CCA end.
Question 20: The 3' CCA sequence of all mature tRNAs is:
- A Added post-transcriptionally and serves as the amino acid attachment site
- B Encoded in the tRNA gene
- C Removed during maturation
- D Present only in prokaryotic tRNA
Explanation: The CCA trinucleotide is added post-transcriptionally to the 3' end of all tRNAs by tRNA nucleotidyltransferase. It carries the amino acid attachment site.
Question 21: Ribozymes are RNA molecules that:
- A Have catalytic activity
- B Only serve structural roles
- C Are restricted to the nucleus
- D Are made of protein
Explanation: Ribozymes are catalytic RNAs — examples include the peptidyl transferase center of the ribosome, self-splicing group I and group II introns, RNase P, and the hammerhead ribozyme.
Question 22: Group I introns undergo self-splicing using:
- A An external guanosine cofactor
- B The spliceosome
- C Adenosine in the branch point
- D ATP hydrolysis
Explanation: Group I introns self-splice via a two-step transesterification mechanism using an external guanosine nucleotide as cofactor — no protein enzyme or ATP required.
Question 23: The phenomenon where different tissues produce different protein isoforms from the same gene is usually due to:
- A Tissue-specific alternative splicing
- B Tissue-specific mutation of the gene
- C Different promoters in different genes
- D Different tRNA repertoire in each tissue
Explanation: Tissue-specific alternative splicing of the same pre-mRNA generates different exon combinations, producing distinct protein isoforms tailored to each tissue.
Question 24: In prokaryotes, transcription and translation are:
- A Coupled (occur simultaneously in the same compartment)
- B Separated in time and space
- C Both occur only in the cytoplasm but are separated by time
- D Both occur only in the nucleus
Explanation: Because prokaryotes lack a nuclear envelope, transcription and translation occur simultaneously in the same compartment, allowing coupled transcription–translation.
Question 25: Capping, splicing, and polyadenylation are collectively known as:
- A mRNA processing
- B Transcription elongation
- C Translation initiation
- D DNA replication
Explanation: These three modifications convert primary (pre-mRNA) transcripts into mature, export-competent, translation-ready mRNA. They are collectively called mRNA processing.