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U of M GCD 3022 - Ch 12: Transcription in Bacteria and Eukaryotes
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GEN 3022 1ST eDITION Lecture 17Outline of Last Lecture I. Overview of DNA replicationa. Replication patternsi. Antiparallelii. Chargraff’s ruleiii. Semiconservativeb. SummaryII. Proposed models of DNA replicationa. Conservative modelb. Semiconservative modelc. Dispersive modelIII. Experimenta. E. coli growthb. Light and half-heavy DNA typesIV. Origin of bacterial DNA replicationa. Origin of replication (oriC)b. Patterns of bacterial DNA replicationV. Synthesis of new DNA strandsa. DNA helicaseb. Topoisomerase II (DNA gyrase)c. Primased. DNA Polymerasese. LigaseVI. Synthesisa. Leading strands b. Lagging strandsc. DNA polymerase I actiond. DNA ligase actionVII. Fidelity mechanismsa. High fidelity in DNA replicationsi. Three reasonsb. Proofreading activity of DNA polymeraseVIII. Eukaryotic genomesIX. Telomeres and DNA replicationa. Telomeric sequencesb. Telomerase c. Telomere length and cancerThese 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 LectureI. Transcription DefinitionII. Gene expressiona. Structural genesb. mRNAc. central dogma of genetics III. Overview of Transcriptiona. Regulation of RNA synthesisb. Role of proteinsc. Gene expressionIV. Functions of RNA transcriptsa. Polypeptidesb. RNA moleculesc. Nonstructural genesV. Transcription in bacteriaa. Promotersb. Initiationi. RNA polymeraseii. Holoenzymeiii. Closed and open complexesc. Elongationi. Overviewii. Template and coding strandsd. Terminationi. Overviewii. Termination mechanisms in E. coliVI. Transcription in Eukaryotesa. Major differencesb. RNA polymerasesi. RNA polymerase Iii. RNA polymerase IIiii. RNA polymerase IIIc. Sequences of Eukaryotic structural genesi. Core promoterii. Regulatory elementsiii. Transcription factorsiv. Cis and Trans acting elementsVII. RNA modificationa. Colinearity of gene expressionb. RNA splicing/excisioni. Introns ii. Exonsiii. Spliceosome and subunitsiv. snRNP’sv. Intron advantagec. Processingd. Cappingi. Overviewii. 7-methylgaunosine cape. Polyadenylation (tailing)i. polyA tailii. mechanismVIII. Identification of Introns via microscopya. The experimentb. The resultIX. RNA editinga. Common types of editingi. Addition or deletion of basesii. Conversion of basesCurrent LectureI. Transcription Definition: the act or process of making a copya. 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 expressiona. 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 Transcriptiona. 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 traitIV. Functions of RNA transcriptsa. Polypeptides: functional products of RNA transcriptsb. RNA molecules: never translated, final functional products are RNA moleculesc. 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 bacteriaa. 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. Initiationi. RNA polymerase: catalyzes synthesis of RNA ii. Holoenzyme: composed of core enzyme and sigma factor, binds loosely tothe 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 releasedc. Elongationi. Overview: when the core enzyme slides down the DNA to synthesize an RNA strandii. 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. Terminationi. 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 polymeraseii. Termination mechanisms in E. coli1. 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 sequenceVI. Transcription in Eukaryotesa. Major differences: larger, more complex molecules; more genes that encode proteins required; more regulationb. RNA polymerasesi. 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 genec. Sequences of Eukaryotic structural genesi. 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 shortii.


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U of M GCD 3022 - Ch 12: Transcription in Bacteria and Eukaryotes

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