Transcription

• The process of Transcription is broken down into 3 stages: Initiation, Elongation, Termination, and Post-transcriptional modifications
• Initiation begins as RNA polymerase binds to the DNA at the promoter.
• The promoter of a gene is characterized by a TATA box, which is an area of repeating Thymines and Adenines
• No primer is needed for RNA Polymerase
• RNA polymerase reads DNA in its 3' to 5' direction. This means RNA polymerase constructs new RNA in the 5' to 3' direction
• The strand opposite to the template strand is called the coding strand
• As RNA polymerase unwinds the DNA the new RNA strand continues to get built and released as a single nucleotide strand and the DNA helix reforms behind it.
• One one RNA polymerase moves beyond the promoter, another RNA polymerase can begin the same process
• Transcription is terminated when RNA polymerase recognizes a termination sequence, which is a string of Adenines on the DNA
• pre-mRNA is vulnerable to enzymes in the cytosol. It also has non coding regions that need to be sliced
• An enzyme called poly-A polymerase adds 50-250 adenines to the 3' end of pre-mRNA, creating a poly(A) tail that protects the RNA from enzymes in the cytosol
• On the 5' end of the pre-mRNA, a 5' cap of 7 guanines are added. This allows the mRNA to attach to the ribosome.
• pre-mRNA has non-coding regions called introns, and coding regions called exons
• Splicing occurs in a spliceosome. snRNPs bind to the intron, and loop it out, bringing the 2 exons closer together. The spliceosome forces the beginning of the intron to start bonding to itself. The snRNPs then cut the intron out, and both the intron and snRNPs are released.