1. DNA Transcription

2. Prokaryotic Cell
Eukaryotic Cell

3. Transcription: Prokaryote
RNA Polymerase unwinds and unzips DNA
(but does not proof-read… why not?)
Complementary NTP’s add to template
DNA strand from 5’ to 3’
RNA Polymerase begins transcribing the DNA at a specific point
RNA strand is identical to the non- coded DNA (and complementary to the template strand)
EXCEPT FOR...

4. Nucleotide (NTP)
Deoxynucleotide (dNTP)
Dideoxynucleotide (ddNTP)

5. Transcription: Eukaryote
Same process as Prokaryotes!
After mRNA is transcribed from DNA then the mRNA has a different fate in prokaryotes and eukaryotes
Prokaryotes immediately begin translating the mRNA. Eukaryotes must process it first.

6. mRNA Processing No mRNA Processing mRNA Processing: • intron/exon
• methyl cap
• poly-A tail

7. Why mRNA is Processed #1 Viral DNA injected into cells
Cells evolve nucleases in cytoplasm that chomp up any RNA or DNA out there
Nucleases can’t get through the nuclear envelope so DNA is safe
mRNA sent out into the cytoplasm must be protected
Methyl cap is a block
Poly A tail is a fuse
mRNA is still chomped up into NTP’s and recycled, but the Poly A tail gives it some time

8. Why mRNA is Processed #2
Eukaryotic DNA is composed mostly of “non-coding DNA” (or “junk DNA”)
We’re still not entirely sure what it does
Was probably inserted by different viruses over time
The ultimate selfish gene just hitching a ride on a successful group of genes…
The introns are the sections of DNA not expressed, the exons are the sections that are expressed (ex-ons are ex-pressed, get it?)
Spliceosome loops out the introns and snips them out
So now we’ve got some mRNA that codes for a protein