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DNA Transcription

DNA Transcription. Prokaryotic Cell. Eukaryotic Cell. 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’.

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DNA Transcription

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  1. DNA Transcription

  2. Prokaryotic Cell Eukaryotic Cell

  3. Transcription: Prokaryote • RNA Polymeraseunwinds 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

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