Here is the completely updated `question.php`.
I added the missing `$breadcrumbs` array and defined `$category_name` and `$topic_name` right before the header is included. This ensures that `header.php` generates the correct Breadcrumb Schema, page title, and meta description for single question pages.
Replace your entire `question.php` with this:
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RNA Processing Questions
Q.
In eukaryotes, RNA processing of pre-mRNA occurs primarily in the:
Cytoplasm
Mitochondria
Ribosome
Nucleus
Explanation:
Pre-mRNA is processed in the nucleus before export to the cytoplasm. Processing includes 5' capping, splicing, and 3' polyadenylation.
Q.
Which of the following is NOT a step in eukaryotic pre-mRNA processing?
3' polyadenylation
Translation of the mRNA
Intron splicing
5' capping
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.
Q.
The 5' cap of eukaryotic mRNA consists of:
7-methylguanosine linked by a 5'-5' triphosphate bond
A short RNA primer
A chain of ~200 adenine residues
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.
Q.
The primary function of the 5' cap is to:
Provide the poly-A tail attachment site
Encode the start codon
Protect mRNA from degradation and aid in translation initiation
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.
Q.
The poly-A tail is added to the 3' end of eukaryotic mRNA by:
Primase
RNA polymerase II
Spliceosome
Poly-A polymerase (PAP)
Explanation:
After cleavage at the polyadenylation signal (AAUAAA), poly-A polymerase (PAP) adds ~150–250 adenine residues to the 3' end without a template.
Q.
The consensus polyadenylation signal in eukaryotic pre-mRNA is:
GGGCGG
CCAATCA
AAUAAA
TATAAT
Explanation:
The hexanucleotide AAUAAA (in RNA) is the highly conserved polyadenylation signal that directs cleavage and poly-A addition.
Q.
The poly-A tail of mRNA primarily functions to:
Provide the 5' cap structure
Increase mRNA stability and translation efficiency
Encode amino acids at the C-terminus
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.
Q.
Introns are removed from pre-mRNA by a process called:
Capping
Splicing
Editing
Polyadenylation
Explanation:
Splicing removes introns and joins exons to produce mature mRNA. The reaction is catalyzed by the spliceosome.
Q.
The spliceosome is composed of:
DNA and histones
Only protein enzymes
rRNAs only
snRNAs and associated proteins
Explanation:
The spliceosome consists of five snRNPs (U1, U2, U4, U5, U6), each containing an snRNA and associated proteins, plus numerous additional protein factors.
Q.
The 5' splice site consensus sequence in pre-mRNA is:
AG
AU
GU
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.
Q.
The 3' splice site consensus sequence in pre-mRNA is:
AG
GG
GU
AU
Explanation:
The 3' splice site (acceptor) is characterized by the dinucleotide AG, which is preceded by a polypyrimidine tract.
Q.
The branch point adenosine residue in pre-mRNA splicing is critical for:
Adding the 5' cap
Formation of the lariat intermediate in the first transesterification
Terminating transcription
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.
Q.
Alternative splicing allows:
Reversal of transcription
Production of multiple proteins from a single gene
Production of multiple genes from one protein
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.
Q.
Approximately what percentage of human genes undergo alternative splicing?
Less than 5%
About 10%
About 25%
More than 90%
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.
Q.
RNA editing is:
Another name for splicing
A post-transcriptional change in RNA sequence that differs from the DNA template
The same as polyadenylation
Addition of the 5' cap
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.
Q.
Apolipoprotein B (ApoB) mRNA undergoes tissue-specific RNA editing in the intestine by:
A U→C edit
Alternative splicing
A C→U edit creating a premature stop codon
A large deletion
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).
Q.
The enzyme adenosine deaminase acting on RNA (ADAR) catalyzes:
Guanine → adenine editing
Adenosine → inosine (A→I) editing
Cytosine → uracil editing
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.
Q.
Mature mRNA is exported from the nucleus to the cytoplasm through:
The Golgi apparatus
The endoplasmic reticulum
Nuclear pore complexes
Gap junctions
Explanation:
Nuclear pore complexes (NPCs) mediate transport of mature mRNA and other RNAs across the nuclear envelope in an energy-dependent manner.
Q.
tRNA and rRNA undergo extensive post-transcriptional processing, including:
5' capping and polyadenylation
Cleavage and base modifications
Reverse transcription
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.
Q.
The 3' CCA sequence of all mature tRNAs is:
Added post-transcriptionally and serves as the amino acid attachment site
Removed during maturation
Encoded in the tRNA gene
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.
Q.
Ribozymes are RNA molecules that:
Are made of protein
Are restricted to the nucleus
Only serve structural roles
Have catalytic activity
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.
Q.
Group I introns undergo self-splicing using:
The spliceosome
An external guanosine cofactor
ATP hydrolysis
Adenosine in the branch point
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.
Q.
The phenomenon where different tissues produce different protein isoforms from the same gene is usually due to:
Different tRNA repertoire in each tissue
Tissue-specific alternative splicing
Different promoters in different genes
Tissue-specific mutation of the gene
Explanation:
Tissue-specific alternative splicing of the same pre-mRNA generates different exon combinations, producing distinct protein isoforms tailored to each tissue.
Q.
In prokaryotes, transcription and translation are:
Both occur only in the cytoplasm but are separated by time
Separated in time and space
Both occur only in the nucleus
Coupled (occur simultaneously in the same compartment)
Explanation:
Because prokaryotes lack a nuclear envelope, transcription and translation occur simultaneously in the same compartment, allowing coupled transcription–translation.
Q.
Capping, splicing, and polyadenylation are collectively known as:
mRNA processing
DNA replication
Transcription elongation
Translation initiation
Explanation:
These three modifications convert primary (pre-mRNA) transcripts into mature, export-competent, translation-ready mRNA. They are collectively called mRNA processing.