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:
```php
Transcription Questions
Transcription is the synthesis of an RNA molecule using DNA as a template, catalyzed by RNA polymerase.
Q.
Which enzyme synthesizes RNA during transcription in bacteria?
DNA-dependent RNA polymerase
Reverse transcriptase
DNA polymerase III
Primase
Explanation:
Bacterial DNA-dependent RNA polymerase is a multi-subunit enzyme that catalyzes RNA synthesis using a DNA template.
Q.
The DNA strand that is copied during transcription is called the:
Lagging strand
Template (antisense) strand
Leading strand
Coding (sense) strand
Explanation:
The template (antisense) strand is read by RNA polymerase to produce complementary RNA. The other strand is called the coding (sense) strand.
Q.
The coding strand of DNA has the same sequence as which molecule (except T→U)?
rRNA
The template strand
tRNA
mRNA (except T→U)
Explanation:
The coding (sense) strand is complementary to the template and therefore matches the mRNA sequence, with thymine replaced by uracil.
Q.
A promoter is best described as:
The 3' untranslated region of mRNA
A protein that unwinds DNA
The origin of DNA replication
A DNA sequence upstream of a gene where RNA polymerase binds
Explanation:
The promoter is a DNA sequence located upstream of the transcription start site that binds RNA polymerase and transcription factors to initiate transcription.
Q.
In bacteria, the -10 sequence of the promoter is also known as the:
GC box
TATA box
CAAT box
Pribnow box
Explanation:
The -10 sequence (consensus TATAAT) is called the Pribnow box. It is recognized by the sigma factor of RNA polymerase.
Q.
In bacteria, the -35 sequence of the promoter is primarily recognized by:
The sigma factor of RNA polymerase
DNA gyrase
The rho termination factor
The TATA-binding protein
Explanation:
The sigma factor (σ) of bacterial RNA polymerase recognizes both -10 and -35 promoter elements, enabling specific initiation of transcription.
Q.
The role of the sigma factor in bacterial transcription is:
Splice introns from mRNA
Direct RNA polymerase to the promoter for initiation
Terminate transcription
Catalyze elongation of RNA
Explanation:
Sigma factor directs RNA polymerase to promoters, initiates transcription, and is released after elongation begins. Different sigma factors allow responses to environmental changes.
Q.
In eukaryotes, which RNA polymerase transcribes messenger RNA (mRNA)?
RNA polymerase II
RNA polymerase III
RNA polymerase I
RNA polymerase IV
Explanation:
RNA polymerase II transcribes protein-coding genes into mRNA (and many non-coding RNAs). RNA polymerase I makes rRNA, and III makes tRNA and 5S rRNA.
Q.
In eukaryotes, which RNA polymerase transcribes ribosomal RNA (rRNA)?
RNA polymerase III
RNA polymerase IV
RNA polymerase II
RNA polymerase I
Explanation:
RNA polymerase I is dedicated to transcribing the large rRNA precursor in the nucleolus, which is processed into 18S, 5.8S, and 28S rRNAs.
Q.
In eukaryotes, which RNA polymerase transcribes transfer RNA (tRNA)?
RNA polymerase IV
RNA polymerase III
RNA polymerase II
RNA polymerase I
Explanation:
RNA polymerase III transcribes tRNA genes, 5S rRNA, and other small non-coding RNAs.
Q.
The TATA box is a promoter element found in:
The ribosome binding site in mRNA
Introns only
Many eukaryotic promoters
All bacterial promoters
Explanation:
The TATA box is a conserved AT-rich sequence in many eukaryotic promoters, typically about 25–30 bp upstream of the transcription start site.
Q.
General (basal) transcription factors in eukaryotes function to:
Splice mRNA introns
Terminate transcription at specific sites
Assemble with RNA polymerase II at the promoter to initiate transcription
Synthesize poly-A tails
Explanation:
Basal transcription factors (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH) assemble with RNA polymerase II at the promoter to form the preinitiation complex and enable transcription.
Q.
The 5' cap added to eukaryotic mRNA during processing is:
A chain of ~200 adenine nucleotides
7-methylguanosine linked via a 5'-5' triphosphate bridge
A chain of ~200 thymine nucleotides
A short peptide tag
Explanation:
The 5' cap is a 7-methylguanosine linked via a 5'-5' triphosphate bridge. It protects the mRNA from degradation and helps ribosomes recognize the transcript.
Q.
The poly-A tail added to eukaryotic mRNA is composed of:
Guanine nucleotides
Adenine nucleotides
Uracil nucleotides
Cytosine nucleotides
Explanation:
The poly-A tail is a stretch of ~150–250 adenine residues added post-transcriptionally to the 3' end of mRNA, increasing stability and translation efficiency.
Q.
Introns in primary RNA transcripts are:
Sequences that encode the 5' cap
Intervening non-coding sequences removed during splicing
Signals that initiate transcription
Protein-coding sequences retained in mRNA
Explanation:
Introns are intervening non-coding sequences removed from the primary transcript during RNA splicing. Exons are retained and joined to form mature mRNA.
Q.
Exons are best described as:
Non-coding sequences removed during splicing
Terminator sequences only
Coding sequences retained in mature mRNA after splicing
Promoter sequences only
Explanation:
Exons are the coding segments of a gene that are retained in mature mRNA after introns are spliced out.
Q.
The spliceosome is a complex that:
Catalyzes intron removal from pre-mRNA
Synthesizes RNA from DNA
Translates mRNA into protein
Adds the poly-A tail to mRNA
Explanation:
The spliceosome is a large RNA-protein complex (containing snRNAs and many proteins) that catalyzes intron removal and exon joining during mRNA processing.
Q.
Alternative splicing of a pre-mRNA allows a single gene to produce:
Only one protein isoform
Multiple protein isoforms from one gene
DNA from RNA
Only non-coding RNAs
Explanation:
Alternative splicing varies which exons are retained in the mature mRNA, so one gene can generate multiple distinct protein isoforms.
Q.
Rho-dependent termination in bacteria requires:
The TATA box
The Rho protein (an ATP-dependent helicase)
A poly-A tail
The sigma factor
Explanation:
Rho-dependent termination uses the Rho protein, an ATP-dependent helicase that binds the emerging RNA and disrupts the RNA-DNA-RNA polymerase complex.
Q.
Rho-independent termination in bacteria involves:
The Rho protein
A 5' cap structure
The sigma factor
A GC-rich hairpin in the RNA followed by a run of uridines
Explanation:
Rho-independent (intrinsic) termination depends on a GC-rich inverted repeat that forms a stable stem-loop followed by a run of uridines in the RNA, causing polymerase pausing and release.
Q.
Reverse transcriptase synthesizes:
RNA from a DNA template
Protein from mRNA
DNA from an RNA template
Lipids from DNA
Explanation:
Reverse transcriptase is an RNA-dependent DNA polymerase that makes DNA from an RNA template — the reverse of normal transcription.
Q.
A polycistronic mRNA:
Encodes one protein from many transcripts
Encodes multiple proteins from one transcript
Contains no coding sequences
Is unique to eukaryotes
Explanation:
Polycistronic mRNAs contain multiple coding regions (cistrons) under a single promoter, allowing several proteins to be translated from one transcript — common in bacteria and absent from most eukaryotic mRNAs.
Q.
An operon is:
A eukaryotic enhancer element
A type of intron
A cluster of co-transcribed genes regulated by a single promoter
The origin of DNA replication
Explanation:
An operon is a cluster of prokaryotic genes controlled by a single promoter and regulatory sequences, allowing coordinated expression.
Q.
Enhancers are DNA elements that:
Increase transcription from a distance, independent of orientation
Direct splicing of introns
Terminate transcription
Encode the poly-A tail
Explanation:
Enhancers are distal DNA elements that increase transcription of a target gene when bound by specific transcription factors — often from a distance and independent of orientation.