1. All three eukaryotic polymerases contain subunits homologous to subunits that
ID: 209641 • Letter: 1
Question
1. All three eukaryotic polymerases contain subunits homologous to subunits that make up the bacterial RNA polymerase (2). However, the eukaryotic polymerases contain additional subunits that are not homologous to these proteins. Which of the following provides one explanation for the role of these subunits in transcription?
A. Eukaryotic RNA polymerase complexes are larger and these additional subunits are required only to provide the complex with more stable protein–protein interactions.
B. Promoter regions and regulatory elements differ for all three eukaryotic RNA polymerases. Additional subunits are required to facilitate the interaction between the polymerase complex and DNA.
C. The eukaryotic RNA polymerases synthesize RNA using a different reaction mechanism that requires these subunits.
D. Eukaryotic RNA transcripts are longer, so transcription requires the activities of additional subunits.
A. during transcription initiation
B. after transcription initiation but early in elongation
C. near the end of elongation
D. during transcription termination
E. after transcription termination
Explanation / Answer
Answer A: Correct option is (A). Eukaryotic RNA Polymerases complexes are larger and these additional subunits are required only to provide the complex with more stable protein- protein structure. Transcription initiation in an eukaryotic cell is a more complex process. It requires the presence of transcriptional activator proteins, which bind to specific sequences in DNA. These subunits play an important role in transcription initiation in eukaryotic cells.
Answer B: 5' m7G cap is added to an mRNA transcript; after transcription termination. So correct answer is option (E). Pre- tRNA, and pre- rRNA undergo processing like cleavage, addition of nucleotides and chemical modification after synthesis. Although both prokaryotes and eukaryotes modify pre tRNA and pre- rRNA, eukaryotes very extensively process pre mRNA destined to become mRNA. After the completion of transcription transcript undergoes in some modification which includes 5'capping, 3' cleavage/polyadenylation, splicing and RNA editing after that processed RNA transported to the cytoplasm, where they are translated by ribosomes.
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