Transcription Flashcards
(27 cards)
What is transcription
The conversion of DNA into RNA using base pairing
What is core machinery of transcription
RNA polymerases (depending on RNA type) and proteins that form the initiation complex
What are specific factors in transcription
Proteins that induce or repress expression of selective genes (transcription factors)
What are the 3 main steps of transcription
Initiation, elongation and termination
What is the RNA product complementary and anti parallel to
The template/ non coding strand of DNA
What is the RNA product identical to
The non-template/ coding strand of DNA
What direction does the coding/ non-template strand run
5’-3’
What direction does the RNA product run
5’-3’
What direction does the non-coding/template strand run
3’-5’
Which RNA polymerase transcribes the gene that encodes most ribosomal RNA (rRNA)
RNA polymerase I
Which RNA polymerase transcribes the gene that encodes mRNA
RNA polymerase II
Which RNA polymerase transcribes the gene that encodes tRNA and 1 rRNA
RNA polymerase III
How many different RNA polymerases are in eukaryotes
3
How many different RNA polymerases are in prokaryotes
1
What happens during stage 1 of transcription (initiation)
RNA pol binds to the template DNA promoter region and forms the initiation complex
What happens during stage 2 of transcription (elongation)
RNA pol synthesises the RNA strand using the template strand pf DNA
What happens during stage 3 of transcription (termination)
RNA strand is released at stop signal and the RNA polymerase complex is disassembled
What is the TATA box
Promoters on genes transcribed by RNA pol II contain a TATAAA sequence 30bp upstream of +1recognised by the initiation complex and RNA pol II
Describe initiation of transcription for a gene transcribed by RNA pol II
1) TAT binding protein (TBP) binds to the TATA box
2) other TFS and RNA pol II are recruited to form the initiation complex
3) RNA polymerase unwinds local regions of DNA so transcription can start at +1 site
Describe what happens during elongation of a gene transcribed by RNA pol II
1) RNA pol unwinds the double stranded DNA and moves along the template strand in the 3’-5’ direction
2) RNA nucleotides are added in in the 5’-3’ direction , elongating the RNA strand
How does the newly synthesised strand of RNA exit the transcription bubble
Via the exit channel
Describe the steps of transcription termination
1) RNA is released and the double helix is rewound
2) RNA pol is released from the template strand and recycled
How does transcription termination differ between the 3 RNA pols in eukaryotes
Pol I and III require termination signals but II does not
Describe how RNA pol II transcription is terminated
RNA pol II termination does not occur at specific sequences and keeps transcribing beyond the end of a coding sequence, pre mRNA is then processed and cleaved after (AAUAAA) consensus sequence (poly A tail) while transcription is still occurring, cleavage polyadenylation then happens to the pre-mRNA
