1. TRANSCRIPTION
SBI 4UI – 5.3

3. Transcription
DNA  mRNA
In the nucleus

4. Initiation
Begins when RNA polymerase binds to DNA segment to be copied
Opens the double helix

6. Initiation RNAP binds to what is called the promoter
DNA upstream of the gene to be transcribed
Consists of a string of A’s and T’s
Prior to the “start” codon

7. Elongation RNAP has opened the double helix during initiation
mRNA begins to be built
5’ to 3’ direction
DNA strand used for replication is called the template strand
Strand not used is called the coding strand
Proceeds in the same manner as DNA replication
Except uracil instead of thymine

9. Termination mRNA synthesized until end of gene reached
End is recognized by a terminator sequence
Newly synthesized mRNA dissociates from DNA template

10. Hasta La Vista,
mRNA!

11. Posttranscriptional Modifications
After transcription the mRNA product is known as a primary transcript
5’ cap is added
Protects mRNA
Poly-A polymerase adds ~200 adenine ribonucleotides
Known as capping and tailing

12. Posttranscriptional Modifications
DNA comprised of
Coding regions – exons
Noncoding regions – introns
Introns to not code for part of the protein
Must be removed
Spliceosome proteins cut introns and join exons
mRNA exits nucleus
Introns remain are degraded in the nucleus

14. The Final Product Initiation Elongation Termination
Posttranscriptional modifications
Leads to… mRNA transcript
Errors during transcription
Protein susceptible to degradation once synthesized

15. The Final Product

16. Questions?

17. To Do
Section 5.3
Understanding Concepts #1-9