DNA Transcription

DNA Transcription

Synopsis: DNA Transcription is the synthesis of RNA from a DNA template where the code in the DNA is converted into a complementary RNA code.
Setting: Promoter Region
Characters: Antisense or template strand, Sense strand or coding strand, RNA polymerase II, transcription factors, 5' cap, poly-A tail, introns, exons
Plot: Initiation, Elongation, Termination

ACT I: Initiation

• Transcription factors (TFs) identify and bind to the promoter region. (TATA Box)
• RNA polymerase II binds to the transcription factors in DNA and forms a transcription initiation complex.

ACT II: Elongation

• RNA Polymerase II synthesize a strand of pre-mRNA (complementary to template strand) by adding nucleotides to the 3' end of the growing pre-mRNA. Transcription goes from upstream towards downstream of the DNA strands in a 5' to 3' direction.
• Pre-mRNA is anti-parallel with the template strand (Antisense), and it's similar with the coding strand (Sense) except U(pre-mRNA) and T(DNA strand). Uracil replaces thymine within the pre-mRNA.

ACT III: Termination

• RNA Transcription stops when it reaches the terminator region (AAUAAA).
• The pre-MRNA will undergo modification to mRNA.
•  A 5' cap which has an altered form of guanine is added to the pre-mRNA strand for protectionand to indicate to ribosomes where to start. Also, a poly-A-tail is added to the 3' end (series of adenine nucleotides). 
• RNA splicing occurs  where introns (non-coding regions) are removed from the transcript by making a loop, leaving only exons (coding segments), which is done by the splicosome, consisting of snRNPs and snRNA.
• As a result, the mRNA strand is complete and ready for transport to the ribosomes.

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