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Question 2#

All of the following transcription mechanisms occur in eukaryotes EXCEPT:

A. Chromatin structure changes to allow DNA to be accessible to the polymerase
B. Three separate RNA polymerases are involved
C. Proteins or initiation factors are not required
D. Often packaged with histone and nonhistone proteins into chromatins

Correct Answer is C


Transcription mechanisms in eukaryotes differ from those in prokaryotes. The unique features of eukaryotic transcription are as follows:

  1. Three separate RNA polymerases are involved in eukaryotes: RNA polymerase I transcribes the precursor of S.SS, ISS, and 28S rRNAs; RNA polymerase II synthesizes the precursors of messenger RNA (mRNA) as well as microRNA; and RNA polymerase III makes tRNAs and 5S rRNAs.
  2. In eukaryotes, the initial transcript is often the precursor to final mRNAs, tRNAs, and rRNAs. The precursor is then modified and/or processed into its final functional form. RNA splicing is one type of processing to remove the noncoding introns (the region between coding exons) on an mRNA.
  3. In contrast to bacterial DNA, eukaryotic DNA often is packaged with histone and nonhistone proteins into chromatins. Transcription will only occur when the chromatin structure changes in such a way that DNA is accessible to the polymerase.
  4. RNA is made in the nucleus and transported into cytoplasm, where translation occurs. Therefore, unlike bacteria, eukaryotes undergo uncoupled transcription and translation.