Transcription Flashcards
RNA is transcribed in the _____ to ______ direction
5’ to 3’
Prokaryotic initiation of transcription
- TATAAT sequence serves as part of promoter region
- requires the association of RNA polymerase and sigma factors to initiate transcription
- different sigma factors can be recruited
- initiation occurs when RNA polymerase binds to sigma subunit to create a holoenzyme which is able to unwind DNA
Prokaryotic Elongation during transcription
RNA polymerase is able to unwind DNA revealing both strands
Can then begin to catalyze the production of RNA strand
elongates the strand by adding individual nucleotides
Can restore the DNA back to its double helix
Prokaryotic Termination during transcription
- Rho-independent sequences are transcribed and then fold back on themselves to create a loop which pauses the RNA polymerase and releases the mRNA
- Rho-dependent terminators use a specific prokaryotic protein or rho- factor which moves along the RNA to destabilize the interaction between DNA and RNA leading to the release
Eukaryotic initiation of transcription
General transcription factors are required to mediate the binding of RNA polymerase to a promoter
Eukaryotic elongation during transcription
RNA polymerase reads a sequence of DNA and can produce the complementary strand of RNA
Eukaryotic termination during transcription
RNA Polymerase 2: depends on poly (A) dependent mechanism of termination
RNA Polymerase 3: have transcription terminated after transcription of a termination sequence in a mechanism that resembles the rho-dependent sequence
RNA Polymerase 1: transcription is terminated using a specific eukaryotic termination factor
RNA polymerase 1
transcribes genes for ribosomal RNA
RNA polymerase 2
transcribes mRNA
RNA polymerase 3
transcribes genes for tRNA
5’ Cap
addition of a modified guanosine to the 5’ end to make a cap
ensures stability of mRNA molecule
ensures the export of mRNA from the nucleus
help with the attachment of the ribosome and initiation of translation
Poly A tail
tail made up of adenines added to the 3’ end
help protect against ribonuclease enzymes that target phosphodiester bonds
Spliceosome
composed of 5 small nuclear ribonucleoproteins which are able to recognize the splice site
Chaperonins
assist in protein folding to ensure the protein is folded correctly
Splicing
RNA and splice some form complementary base pairing
- catalyzes a reaction which allows specific hydroxyl group to attack the phosphodiester bond essentially cutting it
- intron forms a loop which allows the two exons to form back together