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 5’→3’ 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 of general 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