1 / 16

Transcription: From DNA to RNA

Transcription: From DNA to RNA. Chapter 8.2. Why RNA?. 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 mRNA is a complementary copy of a gene that CAN leave the nucleus. Messenger RNA.

sharne
Télécharger la présentation

Transcription: From DNA to RNA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Transcription:From DNA to RNA Chapter 8.2

  2. Why RNA? • 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 • mRNA is a complementary copy of a gene that CAN leave the nucleus Messenger RNA

  3. Transcription:Making mRNA from DNA Four phases • Initiation • Elongation • Termination • Processing

  4. RNAP 1) Initiation • RNA polymerase (RNAP) binds to the double stranded DNA molecule at a promoter sequence • Promoters • always upstream of the gene being transcribed • Determines where RNAP binds and where transcription begins • Usually rich in Thymine and Adenine (“TATA” box) • RNAP has its own built-in helicase activity TATATT

  5. 3´ 5´ A T G T G A C T A C G G G C C C C G P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S 3´ 5´ 2) Elongation • One strand of the unzipped DNA acts as a template for RNA synthesis Template Strand

  6. T C G T G G G A C U G G C G C A C C A C G C U A C G T P P P P P P P P P P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S S S S S S S S S S 3´ 5´ 2) Elongation 3´ 5´ 5´ 3´ Template Strand

  7. 2) 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

  8. 3) Termination • A terminator sequence on the non-transcribed DNA strand tells RNAP when to stop transcribing the mRNA • RNAP is released and reused • mRNA released

  9. 3´ 5´ G G T G C U G G C C A U C C G A C C G A C T A C G G T P P P P P P P P P P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S S S S S S S S S S 3´ 5´ 3) Termination mRNA Template Strand

  10. 4) Processing • Occurs only in eukaryotic cells • Why processing? • Remove introns • Protects from degradation in the cytoplasm

  11. 4) Processing • Splicing • mRNA still has bothintrons and exons • We need to removeintrons • Spliceosome - a complex of multiple proteins and snRNA (small nuclear) • snRNA binds a specific mRNA sequences at the beginning and end of an intron forming a loop • Loop is removed by spliceosome

  12. restriction enzymes in cytosol 4) Processing • Protecting the mRNA • From what? • 5’ cap • Modified G added to 5’ endof mRNA • Poly-A tail • Many A added to 3’ end of mRNA

  13. G G G C U C G A U C G A A A A A A A G G A P P P P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S S S S Final mRNA Molecule 5´ 3´ cap mRNA transcript poly A tail

  14. video http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html

  15. Better Video

More Related