1. Transcription
… from DNA to RNA

2. The Central Dogma of Molecular Biology
DNA
RNA
Protein
transcription
translation
replication

4. Why RNA?

5. Why RNA? Not all genes need to be turned on at once.
We can make an RNA transcript of just ONE GENE
Now we can make the right protein at the right time in the right location

6. Why RNA? In EUKARYOTES… DNA cannot leave the nucleus
BUT proteins are built by the ribosomes in the cytosol!
We need a messenger to transfer the genetic code to the ribosomes

7. mRNA
Messenger RNA (mRNA) is a complementary copy of a gene that CAN leave the nucleus

8. Gaining Access to DNA

9. 4 Phases of Transcription
Initiation
Elongation
Termination
Processing (Eukaryotes Only)

10. Initiation
RNA polymerase (RNAP) binds to the double stranded DNA molecule at a promoter sequence (with the help of initiation factors)
It is able to locally unzip DNA with its own built in helicase activity as it constructs an RNA transcript of the DNA

11. RNA Polymerase II

13. Enhancers

14. Promoters DNA sequence upstream of the gene being transcribed
Determines where RNAP binds and where transcription begins
Usually rich in Thymine and Adenine (“TATA” box)

16. Elongation
One strand of the unzipped DNA acts as a template for RNA synthesis S G P T C A 5´ 3´ S G P A T C 3´ 5´
Template Strand

17. Elongation S C P S G P S C P S U P S G P S G P S A P S U P S C P 3´ 5´
Coding Strand 5´ 3´ S G P A T C 3´ 5´
Template Strand

19. Elongation mRNA is transcribed in the 5' to 3' direction
DNA unwinds only in the region of transcription
After transcription DNA recoils
Several RNAPs can work on a single gene at once

20. One more look at Elongation

21. Termination
A terminator sequence on the coding strand tells RNAP when to stop transcribing the mRNA
RNAP is released and reused and mRNA is released

23. Processing
In Eukaryotic cells the RNA transcript is called pre-mRNA (or primary RNA) because it must still be modified before it leaves the nucleus
Why processing?
Remove introns
Protects from degradation in the cytoplasm

24. Introns and Exons
Genes contain both coding regions (exons) and non-coding regions (introns)

25. Introns and Exons
To produce a final mRNA transcript, introns must be removed

26. Splicing

27. Splicing
The Spliceosome is a complex of multiple proteins (snRNPs) and small nuclear RNA (snRNA)
snRNA binds a specific mRNA sequences at the beginning and end of an intron forming a loop
The loop is removed and exons are linked

30. Cap and Tail cap mRNA transcript poly A tail 5´ 3´ S G P S G P U C A S

31. Cap and Tail
To protect RNA from restriction endonucleases in the cytosol, a poly-A tail is added to the 3‘ end of the pre-mRNA
As an attachment site for the ribosome, a 5‘ cap of modified Gs is added