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
Nucleus
Ribosome
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:
A short RNA primer
A chain of ~200 adenine residues
A methylated cytosine residue
7-methylguanosine linked by a 5'-5' triphosphate bond
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:
Protect mRNA from degradation and aid in translation initiation
Encode the start codon
Provide the poly-A tail attachment site
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:
Poly-A polymerase (PAP)
Primase
Spliceosome
RNA polymerase II
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:
AAUAAA
TATAAT
GGGCGG
CCAATCA
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
Encode amino acids at the C-terminus
Direct the mRNA to the mitochondria
Increase mRNA stability and translation efficiency
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:
Polyadenylation
Splicing
Editing
Capping
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
snRNAs and associated proteins
rRNAs only
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.
Q.
The 5' splice site consensus sequence in pre-mRNA is:
CC
AG
GU
AU
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:
AU
GG
AG
GU
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
Adding the poly-A tail
Formation of the lariat intermediate in the first transesterification
Terminating transcription
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:
Removal of the 5' cap
Production of multiple proteins from a single gene
Production of multiple genes from one protein
Reversal of transcription
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 25%
More than 90%
About 10%
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:
A post-transcriptional change in RNA sequence that differs from the DNA template
Another name for splicing
Addition of the 5' cap
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.
Q.
Apolipoprotein B (ApoB) mRNA undergoes tissue-specific RNA editing in the intestine by:
Alternative splicing
A large deletion
A C→U edit creating a premature stop codon
A U→C edit
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:
Uracil → thymine editing
Guanine → adenine editing
Cytosine → uracil editing
Adenosine → inosine (A→I) 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:
Nuclear pore complexes
Gap junctions
The Golgi apparatus
The endoplasmic reticulum
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:
Reverse transcription
5' capping and polyadenylation
Cleavage and base modifications
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:
Removed during maturation
Present only in prokaryotic tRNA
Encoded in the tRNA gene
Added post-transcriptionally and serves as the amino acid attachment site
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:
Only serve structural roles
Are restricted to the nucleus
Have catalytic activity
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.
Q.
Group I introns undergo self-splicing using:
An external guanosine cofactor
The spliceosome
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:
Tissue-specific mutation of the gene
Tissue-specific alternative splicing
Different promoters in different genes
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.
Q.
In prokaryotes, transcription and translation are:
Separated in time and space
Both occur only in the cytoplasm but are separated by time
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:
DNA replication
Transcription elongation
mRNA processing
Translation initiation
Explanation:
These three modifications convert primary (pre-mRNA) transcripts into mature, export-competent, translation-ready mRNA. They are collectively called mRNA processing.