Gene Expression: Transcription Part 2 Flashcards
What is prokaryotic RNA polymerase?
large enzyme that is composed of five subunits; contains the core enzyme and the sigma factor
What are the three stages of transcription?
initiation, elongation, and termination
When does initiation being in prokaryotic transcription?
occurs when RNA polymerase holoenzyme binds to a promoter
What are the two primary sequences on the prokaryotic promoter for transcription?
Pribnow box and the -35 sequence
What two roles does the sigma factor play in helping the polymerase find promoters?
- increases ability of RNA polymerase to recognize promotors
- decreases the nonspecificity affinity of holoenzyme for DNA
What are the four major differences between prokaryotic and eukaryotic transcription?
- location
- RNA polymerase
- regulation
- primary transcripts
Where does transcription occur in prokaryotes and eukaryotes?
prokaryotes = cytoplasm
eukaryoties = in the nucleus
What is unique about translation and transcription in prokaryotes?
they both occur in the cytoplasm and can occur at the same time
What are introns?
intervening sequences = intragenic regions
What are exons?
protein coding regions of the RNA
What is splicing?
prior to RNA being translated, introns must be removed and exons must be joined together
What are the two methods that eukaryotic hnRNA can be modified?
5’ cap and 3’ poly-A tail
splicing
What is the purpose of the 5’ cap?
essential for translation and for preventing digestion of the mRNA by exonucleases
What is the purpose of the 3’ poly-A tail?
preventing digestion of the mRNA by exonucleases
What are the three RNA polymerases in eukaryotes and what is their function?
RNA poly I = transcribes most rRNA
RNA poly II = transcribes hnRNA, snRNA, and miRNA
RNA poly III = transcribes tRNA, long ncRNA, siRNA, miRNA, and rRNA
