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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
Primase
DNA polymerase III
Reverse transcriptase
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
Coding (sense) strand
Template (antisense) strand
Leading 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)?
The template strand
rRNA
mRNA (except T→U)
tRNA
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 origin of DNA replication
A DNA sequence upstream of a gene where RNA polymerase binds
A protein that unwinds DNA
The 3' untranslated region of mRNA
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
Pribnow box
CAAT 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:
DNA gyrase
The sigma factor of RNA polymerase
The TATA-binding protein
The rho termination factor
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:
Terminate transcription
Splice introns from mRNA
Catalyze elongation of RNA
Direct RNA polymerase to the promoter for initiation
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 IV
RNA polymerase III
RNA polymerase I
RNA polymerase II
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 I
RNA polymerase III
RNA polymerase II
RNA polymerase IV
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 I
RNA polymerase III
RNA polymerase IV
RNA polymerase II
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
Many eukaryotic promoters
Introns only
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
A chain of ~200 thymine nucleotides
A short peptide tag
7-methylguanosine linked via a 5'-5' triphosphate bridge
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:
Uracil nucleotides
Adenine nucleotides
Cytosine nucleotides
Guanine 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:
Protein-coding sequences retained in mRNA
Signals that initiate transcription
Intervening non-coding sequences removed during splicing
Sequences that encode the 5' cap
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:
Coding sequences retained in mature mRNA after splicing
Terminator sequences only
Promoter sequences only
Non-coding sequences removed during splicing
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:
Synthesizes RNA from DNA
Translates mRNA into protein
Adds the poly-A tail to mRNA
Catalyzes intron removal from pre-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:
DNA from RNA
Only non-coding RNAs
Multiple protein isoforms from one gene
Only one protein isoform
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 sigma factor
The TATA box
A poly-A tail
The Rho protein (an ATP-dependent helicase)
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 sigma factor
A GC-rich hairpin in the RNA followed by a run of uridines
The Rho protein
A 5' cap structure
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:
Protein from mRNA
Lipids from DNA
DNA from an RNA template
RNA from a DNA template
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:
Contains no coding sequences
Is unique to eukaryotes
Encodes one protein from many transcripts
Encodes multiple proteins from one transcript
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:
The origin of DNA replication
A eukaryotic enhancer element
A type of intron
A cluster of co-transcribed genes regulated by a single promoter
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:
Encode the poly-A tail
Direct splicing of introns
Terminate transcription
Increase transcription from a distance, independent of orientation
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.