BCHM 3050 1st Edition Lecture 22 Outline of Last Lecture I. One gene One enzymeII. TranscriptionIII. Promoters and Consensus SequencesIV. E. Coli RNA PolymeraseV. Initiation and Elongation Stages of Transcription in ProkaryotesVI. Active Genes are Transcribed Many TimesVII. The Role of Rho-FactorOutline of Current Lecture I. Transcription in EukaryotesII. Eukaryotic RNA PolymerasesIII. Eukaryotic PromotersIV. Initiation of Eukaryotic TranscriptionV. EnhancersVI. RNA ProcessingVII. 5’ Cap of Eukaryotic mRNAVIII. mRNA PolyadenylationIX. mRNA SplicingCurrent LectureI. Transcription in Eukaryotesa. Eukaryotes have 3 RNA polymerases with all of their own functionsb. RNA polymerase cannot initiate transcription without initiation factors (or transcription factors) in eukaryotesc. Enhancers and silencers are also present to modify transcriptiond. Many modifications/edits happen to mRNA once it is made in eukaryotes, unlike prokaryotesII. Eukaryotic RNA Polymerasesa. 3 different polymerases differ in location and functionb. Nucleolus is the dense area in the nucleus that makes rRNAs à location of RNA polymerase 1c. Polymerase 2 à mRNAd. Polymerase 3 à tRNAIII. Eukaryotic PromotersThese 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.a. “TATA” box is at -25 bases from the start sight in the promoter region of eukaryotes à ALL eukaryote genes have thisb. Do not need to know the positions of the CAAT box, GC box, etc because their presence varies from gene to genei. TATA box is universal and highly conserved across eukaryotesc. CAAT box – strong promoter that allows the gene to make many, many amount ofthe gened. GC box – “housekeeping” geneIV. Initiation of Eukaryotic Transcriptiona. TF = transcription factorb. Do not need to know the order that the transcription factors come in because they vary from gene to genec. TFIIH – phosphorylates the RNA polymerase; puts phosphate group onto RNA polymerase II and activates it, which is critical for eukaryotes to carry out transcription (Know This!)d. Location of TATA box = -25V. Enhancersa. Enhancer – lives ~1,000-2,000 bp upstream of the promoter usually (sometimes lives downstream of the promoter, but this is very rare)b. Transcription activators are proteins that bind to the enhancer à activators bend/loops the DNA and attaches to RNA polymerase IIc. Activators helps RNA polymerase II to transcribe DNAd. Diseases can result if this does not happene. Enhancer is part of the DNA sequence f. Activator is a protein that binds to RNA polymerase IIVI. RNA Processinga. Making of any type of RNA is known as transcriptionb. Only mRNA goes through translation and makes proteinsc. Premature RNAs are made first, which then go through RNA processing to be modified and create the final RNA productd. When you make an tRNA, it doesn’t come decorated with amino acids until later when it is modifiede. rRNA must be taken to the ribosomes in order to carry out its functionf. Gene is part of a double stranded DNA à RNA polymerase bound to sense strand à Initiation factors (TATA box) bind to promoter à recruit RNA polymerase à activator bound to enhancer à activate RNA polymerase II à expand DNA molecule à mRNA processingVII. 5’ Cap of Eukaryotic mRNAa. mRNA is a single strand of nucleotides bonded by phosphodiester bondsb. Capping – adding a whole extra unit to the 5’ end of the chainc. Methylate guanosine at the 7’ carbon position and attached to the 5’ end of the DNAd. Heavily methylate 5’ end and add 7-mehtyl-guanosinee. Be able to determine what a 5’ cap looks like on the examf. DNA is only in the nucleus, so mRNA takes orders from the DNA and then leave the nucleus to carry the informationg. 5’ cap helps the mRNA to be seen by the ribosomeh. 5’ cap is a recognition site to get the mRNA into the ribosome and prevents digestion/degradation of mRNA by exonucleases i. Exonucleases chew away the mRNA, but they cannot work when 5’ cap is presentVIII. mRNA Polyadenylationa. 5’ cap is added to the 5’ endb. Poly A tail is added to the 3’ end of the RNA strand via the process of polyadenylation by Poly A polymerasec. Poly A polymerase added the Poly A taild. Functions of Poly A tail - Guides mRNA out of the nucleus and prevents degradation of the mRNAe. Both the cap and the tail aid in preventing degradationIX. mRNA Splicinga. The body of the gene should only be made of exons so in order to achieve this, mRNA splicing excises introns out and stiches exons togetherb. Splicing – the process of removing the intronsc. Spliceosome complex – bag of enzymes that will cut out introns and stitch together the exonsd. snRNA attatches to the junction between the exon and the intron à recruits the protein part (enzyme) to that region à splicinge. Spliceosome – mix of snRNA and proteins(ribonucleo protein) that cut out the introni. Intron is called a lariat when cut
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