What is the primary function of DNA polymerase during transcription?
a) Synthesizing RNA from DNA
b) Unwinding the DNA double helix
c) Proofreading newly synthesized RNA
d) Initiating translation
e) Repairing damaged DNA
Rationale: DNA polymerase primarily functions in DNA replication and repair, rather than transcription. During transcription, RNA polymerase is responsible for synthesizing RNA from a DNA template.
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Which of the following is NOT a component of the transcription complex?
a) DNA
b) RNA polymerase
c) Promoter
d) Ribosome
e) Transcription factors
Rationale: The ribosome is involved in translation, not transcription. The transcription complex includes DNA, RNA polymerase, promoter sequences, and transcription factors, which regulate gene expression.
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In eukaryotic cells, where does mRNA processing occur before translation?
a) Nucleus
b) Cytoplasm
c) Golgi apparatus
d) Mitochondria
e) Endoplasmic reticulum
Rationale: mRNA processing, including capping, splicing, and polyadenylation, occurs in the nucleus of eukaryotic cells before mRNA is transported to the cytoplasm for translation.
Which of the following is NOT a post-transcriptional modification of mRNA?
a) Capping
b) Splicing
c) Transcription
d) Polyadenylation
e) Editing
Rationale: Transcription is the process of synthesizing RNA from a DNA template and does not involve post-transcriptional modifications. Capping, splicing, polyadenylation, and editing are all post-transcriptional modifications that occur in eukaryotic mRNA processing.
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Which of the following is NOT a step in translation?
a) Initiation
b) Elongation
c) Termination
d) Transcription
e) Proofreading
Rationale: Transcription is the synthesis of RNA from a DNA template and occurs before translation. Translation involves initiation, elongation, and termination, where amino acids are assembled into a polypeptide chain on the ribosome.
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What is the role of the Shine-Dalgarno sequence in translation?
a) Initiating translation
b) Elongating the polypeptide chain
c) Terminating translation
d) Proofreading mRNA
e) Assisting in mRNA binding to the ribosome
Rationale: The Shine-Dalgarno sequence is found in bacterial mRNA and assists in the binding of mRNA to the ribosome during translation initiation. It helps position the start codon in the correct location for translation to begin.
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Which of the following is a characteristic feature of prokaryotic transcription?
a) Splicing of mRNA
b) Presence of introns
c) RNA processing in the cytoplasm
d) Use of a Shine-Dalgarno sequence
e) Transcription within the nucleus
Rationale: Prokaryotic transcription differs from eukaryotic transcription in several ways, including the absence of splicing, introns, and RNA processing in the cytoplasm. Prokaryotic mRNA contains a Shine-Dalgarno sequence that helps initiate translation.
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What is the function of elongation factors in translation?
a) Initiating translation
b) Extending the mRNA molecule
c) Catalyzing the formation of peptide bonds
d) Moving the ribosome along the mRNA
e) Proofreading the amino acid sequence
Rationale: Elongation factors in translation facilitate the movement of the ribosome along the mRNA molecule, allowing for the stepwise addition of amino acids to the growing polypeptide chain.
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What is the significance of the poly(A) tail in mRNA?
a) Initiating translation
b) Marking the start codon
c) Protecting mRNA from degradation
d) Stabilizing mRNA in the nucleus
e) Catalyzing the formation of peptide bonds
Rationale: The poly(A) tail, added during mRNA processing, helps protect mRNA from degradation by exonucleases and enhances its stability in the cytoplasm, thereby prolonging the lifespan of the mRNA molecule.
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What is the role of release factors in translation termination?
a) Initiating translation
b) Elongating the polypeptide chain
c) Catalyzing the formation of peptide bonds
d) Dissociating the ribosome from the mRNA
e) Proofreading the amino acid sequence
Rationale: Release factors recognize the stop codon during translation termination and catalyze the hydrolysis of the bond between the final tRNA and the completed polypeptide chain, leading to the dissociation of the ribosome from the mRNA.