Eukaryotic cells transcribe DNA into RNA using a more complex system than prokaryotic cells. Their DNA is enclosed in a nucleus, and different RNA polymerases specialize in transcribing different classes of genes. This lesson introduces the three polymerases and explains how transcription initiation begins.
Eukaryotes use three major RNA polymerases, each with at least 10 subunits and a distinct set of transcription factors. This division of labor allows the cell to produce different kinds of RNA through specialized pathways.
All flashcards
What does RNA polymerase I transcribe?
It transcribes most rRNAs, including the 18S, 5.8S, and 28S rRNAs, in the nucleolus. It does not transcribe 5S rRNA.
What is the main product of RNA polymerase II?
RNA polymerase II transcribes protein-coding nuclear genes to produce pre-mRNAs, which are processed into mature mRNAs.
What are the major products of RNA polymerase III?
It transcribes 5S rRNA, pre-tRNAs, and small nuclear pre-RNAs.
How does α-amanitin affect the three polymerases?
Polymerase I is insensitive, polymerase III is moderately sensitive, and polymerase II is extremely sensitive to the toxin.
How does FACT support transcription through chromatin?
FACT temporarily displaces histones to let RNA polymerase pass, then helps restore nucleosomes.
Quiz questions
What role does TFIID play in RNA polymerase II initiation?Answer: It contains TBP, which recognizes the TATA box when present.
What is the usual effect of an enhancer on transcription?Answer: It increases transcription frequency from a regulated gene.
How does FACT help RNA polymerase move through nucleosomes?Answer: It temporarily displaces histones and helps restore nucleosomes afterward.
What commonly happens when RNA polymerase II reaches the end of a protein-coding gene?Answer: It continues about 1,000–2,000 nucleotides downstream before the extra RNA is cleaved.
Which feature is associated with RNA polymerase III termination?Answer: An RNA hairpin structure
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.