central dogma how all cells express genetic information
DESCRIPTION
Gene Expression Machinery in cell determines DNA segments to transcribe Different genes transcribed at different ratesTRANSCRIPT
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