Transcription

ACT I

• Transcription factors attach to the TATA box also known as the promoter
• The sequences before the TATA box are known as upstream, after the TATA box is known as downstream

• Transcription factors that bind to the the TATA box help attract RNA polymerase 2
• Once  RNA Polymerase 2 binds to transcription factors a transcription initiation complex is created and RNA starts transcribing
• A DNA strand can be transcribed  by several RNA polymerase 2, at a time

Act II

• The double stranded DNA is separated at certain points by RNA polymerase 2 
• The strand being transcribed is the template strand ( antisense) the other strand is the coding strand( sense) 
• The  RNA polymerase 2 binds RNA nucleotides to the template base pairs
• As the RNA strands grow they trail off from each polymerase and the DNA strands reform a helix 
• The RNA strand and template strand are anti-parallel
• Genes are read 3'-5' which creates a 5'-3' RNA molecule
• In RNA there is ''U'' instead of ''T" in the base pairs e.g A=U , T=A

Act III

• The terminator signals the end of transcription, it is the sequence AAUAAA
• At the end of the pre-mRNA molecule that was just synthesized a G cap is added to then of 5' and a Poly(A) tail is added at the end of the 3' 
• Introns (junk sequences that must be removed)
•  Extrons ( sequences that must be expressed) 
• The  spliceosome loops and cuts out the introns 
• It is composed of proteins and  snRNP
•  Every snRNPs has  a small nuclear RNA molecule/ snRNA
• The spliceosome also joins the exons, to create a mRNA molecule
• A messenger RNA has now been synthesized from the DNA strands