GEN 3022 1ST eDITION Lecture 17 Outline of Last Lecture I Overview of DNA replication a Replication patterns i Antiparallel ii Chargraff s rule iii Semiconservative b Summary II Proposed models of DNA replication a Conservative model b Semiconservative model c Dispersive model III Experiment a E coli growth b Light and half heavy DNA types IV Origin of bacterial DNA replication a Origin of replication oriC b Patterns of bacterial DNA replication V Synthesis of new DNA strands a DNA helicase b Topoisomerase II DNA gyrase c Primase d DNA Polymerases e Ligase VI Synthesis a Leading strands b Lagging strands c DNA polymerase I action d DNA ligase action VII Fidelity mechanisms a High fidelity in DNA replications i Three reasons b Proofreading activity of DNA polymerase VIII Eukaryotic genomes IX Telomeres and DNA replication a Telomeric sequences b Telomerase c Telomere length and cancer These 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 Outline of Current Lecture I Transcription Definition II Gene expression a Structural genes b mRNA c central dogma of genetics III Overview of Transcription a Regulation of RNA synthesis b Role of proteins c Gene expression IV Functions of RNA transcripts a Polypeptides b RNA molecules c Nonstructural genes V Transcription in bacteria a Promoters b Initiation i RNA polymerase ii Holoenzyme iii Closed and open complexes c Elongation i Overview ii Template and coding strands d Termination i Overview ii Termination mechanisms in E coli VI Transcription in Eukaryotes a Major differences b RNA polymerases i RNA polymerase I ii RNA polymerase II iii RNA polymerase III c Sequences of Eukaryotic structural genes i Core promoter ii Regulatory elements iii Transcription factors iv Cis and Trans acting elements VII RNA modification a Colinearity of gene expression b RNA splicing excision i Introns ii Exons iii Spliceosome and subunits iv snRNP s v Intron advantage c Processing d Capping i Overview ii 7 methylgaunosine cap e Polyadenylation tailing i polyA tail ii mechanism VIII Identification of Introns via microscopy a The experiment b The result IX RNA editing a Common types of editing i Addition or deletion of bases ii Conversion of bases Current Lecture I Transcription Definition the act or process of making a copy a In genetics transcription means making a copy of a DNA sequence into an RNA sequence The structure of DNA is not altered in this process II Gene expression a Structural genes also known as protein encoding genes Encode the amino acid sequence of a polypeptide b mRNA produced by transcription of a structural gene mRNA sequence determines the amino acid sequence of a polypeptide during translation will be discussed in the next chapter Synthesis of polypeptides functional proteins determines an organism s traits c central dogma of genetics path from gene to trait DNA replication transcription and translation III Overview of Transcription a Regulation of RNA synthesis DNA base sequences define the beginning and end of a gene and regulate the level of RNA synthesis b Role of proteins proteins must recognize and act on DNA for transcription to occur c Gene expression the overall process by which the information within a gene is used to produce a functional product which can in concert with environmental factors determine a trait IV Functions of RNA transcripts a Polypeptides functional products of RNA transcripts b RNA molecules never translated final functional products are RNA molecules c Nonstructural genes not translated but do have important cellular functions and can still confer traits in some cases RNA transcript becomes a part of a complex that contains subunit proteins ribosomes spliceosomes signal recognition particles telomerase V Transcription in bacteria a Promoters DNA sequences that promote gene expression direct exact location for the initiation of transcription i Promoters are typically located just upstream of the site where transcription of a gene usually begins ii Most of the promoter region is labeled with negative numbers 35 and 10 are the most common sequence regions for the promoter b Initiation i RNA polymerase catalyzes synthesis of RNA ii Holoenzyme composed of core enzyme and sigma factor binds loosely to the DNA scans DNA and binds tighter to DNA upon encountering the promoter sequence sensed by the sigma factor iii Closed and open complexes binding of RNA polymerase to promoter forms closed complex while the open complex is formed when the TATAAT box in the 10 region is unwound because A T bonds are more easily separated 1 Short RNA strand is made within the open complex this is where the sigma factor is released c Elongation i Overview when the core enzyme slides down the DNA to synthesize an RNA strand ii Template and coding strands DNA strand used for RNA synthesis is the template strand while the opposite DNA strand is called the coding strand has the same base sequence as RNA transcript except for T instead of U in RNA d Termination i Overview termination occurs when the short RNA DNA hybrid of the open complex is forced to separate which releases the newly made RNA as well as the RNA polymerase ii Termination mechanisms in E coli 1 Rho dependent termination requires a protein rho helicase unwinding protein 2 Rho independent termination instrinsic termination does not require rho facilitated by two sequences in RNA uracil rich sequence at 3 end of RNA and stem loop structure upstream of uracil rich sequence VI Transcription in Eukaryotes a Major differences larger more complex molecules more genes that encode proteins required more regulation b RNA polymerases i RNA polymerase I transcribes all rRNAgenes except for 5S rRNA ii RNA polymerase II transcribes all protein encoding structural genes thus synthesizes all mRNA s and transcribes some snRNA genes needed for splicing forms mediator protein complex with general transcription factors iii RNA polymerase III transcribes all tRNAgenes and 5S rRNA gene c Sequences of Eukaryotic structural genes i Core promoter one of two features of eukaryotic promoter sequences produces low level of transcription basal transcription typically TATAAA sequence called the TATA box transcriptional start site relatively short ii Regulatory elements other feature of eukaryotic promoter sequences short DNA sequences that affect the binding of RNA polymerase to the promoter two types 1