Gene expression DNA  RNA  Protein

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Gene expression DNA  RNA  Protein. DNA DNA RNA Protein. Replication. Initiation Elongation Processing Export. Transcription. Degradation. Translation. Initiation Elongation Processing Targeting. Degradation. Chapter 6. Transcription Sections From DNA to RNA - PowerPoint PPT Presentation

Transcript of Gene expression DNA  RNA  Protein

  • Gene expression DNA RNA ProteinDNA




  • Chapter 6TranscriptionSectionsFrom DNA to RNAThe start of the chapter to the end of Mature eucaryotic mRNAs are selectively exported from the nucleus

  • RNA structureRNA is single stranded polymer of C, G, A, U

    Can have secondary structure but typically not a double helix (Fig. 6-6)

  • RNA structuremany types of RNA made:

    mRNA: encodes proteins,

    snRNA: RNA processing

    snoRNA: rRNA processing

    tRNA: translation

    rRNA: translation

  • Transcription initiationDNA acts as a template for RNA synthesis (Fig 6-9)

  • Transcription initiationDNA acts as a template for RNA synthesisSynthesis by RNA polymerase -RNA Pol

    RNA Pol I makes tRNA and rRNA

    RNA Poly II makes mRNA in nucleus

  • Control of transcriptionTranscription initiation by RNA Pol II requires general transcription factors (Fig 6-16)

  • Control of transcription(Fig. 6-16)Transcription start site usually a TATA box (not always)

    TBP (TATA-binding protein) binds, changing DNA structure (Fig 6-18).

    Recruits transcription factor II proteins (TFIIA, B, ) then RNA Pol II

    Collectively the transcription initiation complex

  • Control of transcriptionSince DNA is wrapped around histones, how does RNA Pol gain access to the promoter?

    How does RNA Pol know where to bind?

  • Control of transcription(Fig. 6-19)Transcription initiation also requires: activatorsmediators (or co-activators), chromatin-remodeling proteins

    Activators increase the likelihood of successful transcription initiation

    Mediators allow activators to communicate with RNA Pol II

  • Transcription factorsDNA-binding proteins associate with specific regions on DNA (elements)

    Elements may be as small as 6 nucleotides

    Subtle differences in DNA 3 dimensional structure alter the ability of proteins to bind

  • RNA processingNewly synthesized transcripts (mRNA) are processed (Fig. 6-21):

    Splice out intervening sequences (=introns) leaving expressed sequences (exons)

    Cap 5 end of RNA

    Poly-adenylate 3 end (Poly A+ tail)

  • RNA processingIntrons are removed in spliceosomes ( a complex of proteins and snRNA)

    cut and paste RNA at specific sites (Fig 6-26, 6-29)

    Requires ATP

  • Transcript processing3 end is also processedcut downstream from poly-adenylation site (AU-rich region)

    Poly A polymerase adds 100s of ATPs

    Length of poly A+ tail influences half-life (degradation rate)

  • Transcript exportProteins associated with mRNA mark it for export

    Only mature mRNA is exported from nucleus

    Exit via nuclear pore complexes