BIOLCHEM 415 1st Edition Lecture 36Outline of Last Lecture I. Eukaryotic Cells have three types of RNA polymeraseII. RNA polymerase II requires complex regulationIII. Gene expression is regulated by hormonesIV. Histone acetylation results in chromatin remodelingOutline of Current Lecture V. Mature Ribosomal RNA generated by the cleavage of precursor mRNAVI. tRNA is extensively processedVII. mRNA is modified and splicedVIII. RNA can functions as a catalystCurrent LecturerRNA generated from cleavage of precursor RNA- RNA polymerase I- nucleotide modifications- adding methyl groups, etc…- snoRNP- segments cut out of precursor by RNase enzymetRNA- serve as adaptor (recognizes mRNA code)- RNA polymerase III- RNase P cuts off leader sequence (5’ end)- CCA-adding enzyme (3’ end)- where activated amino acids attachedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.mRNA processed from precursor transcripts- RNA polymerase II1 – addition of cap at 5’ end2 – addition of 3’ poly-adenylate tail3 – removal of introns- intervening RNA - doesn’t get expressed5’ capping- adding GTP to 5’ end of RNA- 5’-5’ triphosphate linkage- methylated CTP- why?- further process - prevents degradation- enhances translationpoly(A) tail- increases translation efficiency - stabilizes- prevents degradation- recognized by PABP – promotes translationSplicing mRNA- discobered 1977 - precursors mRNAs undergo- remove introns- splice together exonsHemoglobin mRNA- capping poly-adenylation splicing Splicing- spliceosome complex- catalyzed by snRNPs1 – U1 snRNP binds at 5’ splice site2 – U2 snRNP binds at branch site3 – binding of U4-U5-U6 tri-snRNP completes spliceosome- splicingrxn- 2 transesterification reactions - no energy needed to break/form phosphodiester bonds- ATP needed to assemble and rearrange spliceosomeSplicing reaction1 – 5’ splice site attacked by 2’ OH group- 3’ OH2 – 3’ splice site attacked by newly formed 3’ OH of upstream exon- lariat (lasso) intermediatesnRNP are catalytic RNAs- U2 snRNA and U6 snRNA are actual catalysts Mutations that affect pre-mRNA splicing cause disease- 15% of all genetic diseases- thalassemia or clotting disorder- AG mutation in 1st intron of hemoglobin β chain gene- some normal mature mRNA and some abnormal - retinitispigmentase- mutation in U4-U5-U6 tri-snRNPalternative splicing- different proteins from same gene- different splicing patterns- splicing site selection determined by binding of transacting splicing factorTranscription and mRNA processing coupled- c-terminal of RNA polymerase IImRNAs can be edited - apobec enzymeRibozymes- RNAs with catalytic function- snRNAs for splicing - ribonuclease P – cleavage of tRNA- rRNA protein synthesis- self-splicing introns -
View Full Document
Unlocking...