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BIO206H5 (60)
Chapter 7.1

Ch.7.1 From DNA to RNA

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University of Toronto Mississauga
George S Espie

From DNA to RNA October-19-11 8:45 AM • Flow of information from DNA to RNA to protein - centraldogma of molecular biology Portions of DNA sequence are transcribed into RNA • Cells can synthesis large amounts of protein whenever necessary • RNA - linear polymer of four different nucleotides linked by phosphodiesterbonds ○ Ribonucleotides - sugar ribose ○ Contains uracil not thymine ○ Single stranded - fold variety of shapes, carry out functions in cells Transcription produces RNA complementary to one strand of DNA • RNA chain determined by complementary base-paringwith DNA template • Ribonucleotidesare added in enzymatically catalyzed reactions • Does not form hydrogen bondswith DNA templatestrand • Copied from a limited region of DNA, few thousand nucleotides long • RNA polymerase ○ catalyze formation of phosphodiester bonds ○ UnwindsDNA ○ Uses ribonucleoside triphosphatesfor energy ○ Can start without primer - not as accurate as DNA, mistake every 10^4 nucleotides • Synthesis of the next RNA starts before the previous one is finished Several types of RNA are produced in cells • Eukaryotes mRNA carry info transcribed for one gene, single protein • Prokaryotes carry for several different proteins • NonmessengerRNAs act as regulatory, structural,and enzymatic components, play key parts in translation of protein • Gene expression is the process of translating DNA to a productthat has effect on cell Signals in DNA tell RNA polymerase where to start and finish • RNA polymerase collides with DNA then binds firmly when promoter is detected,then opens helix, elongates, then encountersterminator, releases DNA and newly madeRNA • Subunit, Sigma factor recognise promoter Prokaryotes ○ disengages after 10 nucleotides ○ Binds with RNA polymerase after termination • Promoteris asymmetrical , one orientation Initiation of eukaryotic gene transcription is a complex process • Has three different RNA polymerases, RNA polymeraseII -> mRNA • RNA polymerase requires accessoryproteins,general transcription factors (GTF) • DNA in eukaryotes are packet into chromatin structure Eukaryotic RNA polymeraserequires general transcription factors • RNA polymerase cannotinitiate transcription in vitro • TFIID binds to TATA box (25 nucleotides upstream), causesdistortion • Other factors then pile on to completethe transcription initiation complex • Addingphosphategroupsto tail of RNA
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