BMB 251 1st Edition Lecture 24 Outline of Last Lecture I. Clicker QuestionsII. Elongation III. Aminoacyl-tRNAiIV. Translation InitiationV. Misfolded/Unfolded proteinsVI. Molecular chaperonesOutline of Current LectureVII. Coding/Template strand and 5’, 3’ endsVIII. Promoter sequences IX. snRNPsX. SpliceosomeCurrent Lecture- Promoter sequences, translation initiation (eu- vs. pro- [sigmal]) + Coding template, 5’, 3’ o DNA is antiparallel and each strand can be replicated by DNA polymerase; either one canbe the template strand for the othero Same as in transcription, either strand can serve as the template for mRNA synthesiso Strand which serves as the template for transcription = template strand and runs the opposite direction of mRNA (3’ to 5’); 3’ of template strand corresponds to 5’ end of mRNA o The other strand (not template) has no purpose during transcription; does not direct synthesis of mRNA but has the same sequence as the mRNA; called the coding strand; runs 5’ to 3’o RNA polymerase opens double stranded DNA (NOT HELICASE!!!) and runs down template strand from 3’ end to 5’ end, so that it can synthesize in 5’ to 3’ direction because new nucleotides are added to the 3’ –OH groupo Ribosome will start making protein message once bound to tRNAi at the 5’ end (corresponds to the amino terminus of protein)o Carboxyl group of first amino acid added (C-terminus) is free and available to attach to the next amino acid; C-terminus corresponds to the 3’ end of mRNAo Promoter in Prokaryotes -1 is not transcribed, anything past +1 is transcribed. About 25 nucleotides upstream you’ll find the TATA box. Sigma factor initiates transcription in prokaryotes; binds to polymeraseThese 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.- Sigma binds to both TATA box and thing that’s 20 nucleotides downstream, which activates the polymerase- Will put in a couple of nucleotides and then dissociates, which begins elongation phaseo Promoter in Eukaryotes TATA box is still present and TBP (TATA binding protein) binds TATA with TFIID (one of the GTFs-general transcription factors)- TATA must have 6 H-bonds with TBP before anything else can happen BRE section is also present here: binds TFIIB The factors then allow the polymerase to bind and is known as the initiator complex TFIIH: it a kinase which phosphorylates the C-terminus and helicase to complete initial unwinding of template from coding strands- SNRNPs and spliceosomeo Within the intron sequence of pre-mRNA, there is a 2’ –OH group with a “special adenine” o This catalyzes the reaction of itself; autocatalytic: one part of the molecule catalyzes another parto 2’ –OH group with A base cuts 3’ end of the first exon sequence, freeing the 5’ end of the introno This 5’ end of intron then cuts the backbone of the next 5’ end of the following exon, freeing the 3’ end of the introno The 5’ end of the intron combines with the special A base to form a lariat and dissociatesfrom the moleculeo The free 3’ end of first exon and 5’ end of second exon then combine to form mRNA o Small nuclear rRNAs (that don’t leave nucleus) complex with proteins to form snRNPs; these can then be held together by RNA-RNA interactions (U6 and U2) which then also hold mRNA as splicing is going ono U5 (snRNP) attaches to the first exon after attacked by the A base and holds it until the second exon is freed as well, that way they can easily combine to make the spliced mRNA
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