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If protein can’t recognize anything that it is supposed to bind, it will bind to rho factor, make it bigger and stall ribosome
oIf it finds what it’s looking for, rho factor remains the same and ribosome can transcribe TRANSCRIPTION IN EUKARYOTES 7-methyl guanosine caps added to 5’ endobinds proteins and protects 5’ from degradationpoly(A) tails added to 3’ endsopoly(A) polymeraseadds poly(A) tails, after cleavage, which are tracts of adenosine monophosphateoenhance stability and play role in transport from nucleus to cytoplasmif introns present, they are removed by RNA splicingosnRNP complexes called “spliceosomes” remove introns and splice exons together RNA polymeraseoAll eukaryotic RNA polymerases require assistance of other proteins called transcription factors in order to initiate synthesis of RNA chainsoI:catalyzes the synthesis of all ribosomal RNAs except small 5S RNA oII:transcribes nuclear genes that encode proteins and perhaps other genes specifying hnRNAsoIII: catazlyzes the synthesis of the transfer RNA molecules, the 5S rRNA molecules, and small nuclear RNAsoIV: small interfering RNAsoV: some siRNAs plus noncoding (antisense) transcripts of siRNA targetgenesInitiation Initiation of transcription by RNA polymerase II requires assistance of severaltranscription factorsPromoters recognized by RNA polymerase IIoCAAT BOX: GGCCAATCT-80oTATA BOX: TATAAAA5’ 3’ and at -30 ofirst A 4bp after TATA: +1 position: transcription start site opresent in RNA polymerase ii PROMOTERSGC BOX: GGGCGGOCTAMER BOX: ATTTGCATElongationOnce RNA polymerases released from initiation complexes, they catalyze RNAchain elongation same way as in prokaryotes5’ ends of mRNA modified by 7-methyl guanosine capsTermination3’ ends produced by endonucleolytic cleavage rather than termination of transcription
ocleavage event occurs 11-30 nucleotides downstream from an AAUAAA sequence and upstream from a GU-rich sequence near end of transcriptoafter cleavage, poly(A) polymerase adds poly(A) tails to 3’ endspolyadenylation Introns:not required for normal gene expression so many eukaryotic genes don’t have introns are spliced out by spliceosomesocomposed of snRNPs (snRNA protein complexes) and proteinsoFive snRNAs: U1, U2, U4, U5, U6Introns are removed, and 2 exons on either side are joined togethero3’end of exon 1joins 5’end of exon 2how to tell if there is intron: if at 5’ end there is a GU and at 3’ end there is an AG, and the intron bonding site UACUAAC (TAC BOX) is presentoeverything between GU and AG is the intron and gets taken out
PROTEIN SYNTHESISRibosomesform peptide bondsodistributed through cells in prokaryotes, located in cytoplasm in eukaryotesocomposed of one large and one small subunits which dissociate when the translation of an mRNA molecule is completedoE.coli:Small 30S subunit and large 50S subunitoMammalian ribosome: Small 18s subunit and large subunit contains 5S, 5.8S, 28So