Central Dogma How all cells express genetic information Gene Expression Machinery in cell determines DNA segments to transcribe Different genes transcribed at different rates RNA Structure Sugar-phosphate backbone Bases Projecting from backbone
Polarity- 5 and 3 ends Sugar Component Of RNA Ribose (RNA) instead of deoxyribose (DNA) Base Component Of RNA Uracil (RNA) instead of thymine (DNA) Folding Of RNA Single-stranded Intramolecular base-pairing Transcription RNA synthesis from DNA template
Chemistry similar to DNA replication RNA Polymerase Local unwinding of DNA Stepwise synthesis of RNA 53
No primer needed RNA release and DNA rewinding Initiation & Termination In Bacteria
s factor recognizes promoter Unwind DNA & begin RNA synthesis s factor dissociates & processive elongation Terminated by destabilizing structure in RNA Determining Template Strand
Dependent upon orientation of promoter Varies from gene to gene Eucaryotic RNA Polymerases
RNA polymerase I rRNA genes (5.8S, 18S, and 28S) RNA polymerase II all protein-coding genes (produce all mRNA) RNA polymerase III tRNA genes, 5S rRNA genes Transcription Initiation By RNA Polymerase II
Requires general transcription factors TFIID/TBP binds to TATA box TFIIH helicase exposes DNA & transcription begins TFIIH kinase causes release ofgeneral factors & processive elongation Transcriptional Activators and Chromatin Modifiers
Activators: DNA binding proteins; promote assembly of RNA polymerase II and general transcription factors Chromatin modifiers allow greater access to DNA mRNA Processing Eucaryotes Synthesis of primary transcript
5 and 3 modifications Removal of introns Capping Of 5 End Addition of 7-methylguanosine Reverse linkage of GMP
Addition of methyl group Intron/Exon Arrangement
coding sequences (exons) separated by intervening sequences (introns) Splicing Reaction two sequential transesterifications
Adenine (branch point) in the intron reacts with 5 splice site Free 3 end of exon reacts with the 5 end of next exon Sequences That Determine Splicing
Three short segments in each intron at beginning, end, and branch point Spliceosome Set of snRNPs each composed of snRNA and proteins
snRNA recognition of splice sites and catalysis Alternative Splicing Multiple proteins encoded by one gene Mutations To Splice Sites
Exon skipping or activation of a cryptic splice site Processing Of 3 End Cleavage at specific sequence
Addition of polyA tail CstF, CPSF bind recognition sequence on RNA
Poly-A polymerase mRNA Export Nuclear pores serve as gates
Proteins binding to processed mRNA mark as export ready Synthesis Of rRNA Multiple copies of genes
Precursor rRNA that is modified and cleaved Nucleolus Ribosome factory rRNA gene clusters
Transcription, processing, assembly