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BIOB11H3 (13)
Dan Riggs (8)
Chapter 11

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University of Toronto Scarborough
Biological Sciences
Dan Riggs

Chapter 11Gene Expression From Transcription to Translation111 The Relationship Between Genes and ProteinsArchibald Garrod1908 People have rare inherited disease caused by enzymesalcaptonuria disease bc urine becomes dark when exposed to air Patients lacked enzymes in blood that oxidizes homogentistic acidcompound from breaking down aa ohenlyalanine and tyrosineGeorge Beadle and Edward Tatum1040 NEUROPORABread mould that forms in normal simple medium organic Csour e inorganic salts and biotin Some organisms should be sensitive to enzymatic deficienciesIrradiate mold spores and screen them for mutationtested for ability to grow in minimal medium 2 cells unable to grow on minimal medium 1 needed vitamin B6pyridoxine and other needed B1thiamine Gene carries information for construction on particular enzymeenzymes composed of 1 polypeptide chain each encoded w own geneone gene one polypeptideWhat is the molecular nature of the defect in a protein cause by a genetic mutation Mutation causing sickle cell anaemiaHemoglobin 4 polypeptides Cleave preparation in normal and sickle cell forms of haemoglobins Analyzed peptide fragments by paper chromatography Of 30 1 migrated differently in 2 preparationsubstitution of valineOverview of the Flow of Information through the CellMessenger mRNAIntermediate bw gene and polypeptide Discovered by Francoise Jacob and Jacque Monod Assemble d as complementary copy of 1 DNA strandTranscription Synthesis fo RNADNAUsed to allow cell to separate information storage form information utilizationinfo imparted to smaller mobile nucleic acid to cytoplasm In cytoplasmmRNA serves as template to incorporate aa to nucleotide sequenceAlso used to greatly amplify synthetic outputTranslation Protein synthesis in cytoplasm Requires participation of many componentsRIBOSOMES Ribosomes are nonspecific components of translation machinerycan be programmed to translate informationRibosomal RNArRNA Ribosomes with both proteins and RNA each transcribed from 1 of DNA strands Provide structural support and catalyze chemic rxnTransfer RNAtRNA Translate information in mRNA to amino acid alphabetRNA gold to complex 3D shape RNA folding driven by formation of regions having complementary ba se pairs Basepaired regions form doublestrandedhelical stemsconnected to signle0stranded loops RNA contain nonstandard base pairs and modified NbasesRNA important in cellular metabolism small nuclear RNAsnRNA small nucleolarRNAsnoRNA small interfering RNAsiRNA microRNAmiRNA112 An Overview of Transcription in Both Prokaryotic and Eukaryotic CellsTranscriptionDNA strand provides info for synthesis of RNA strandDNADependent RNA polymeraseRNA Polymerase Responsible for transcription in prokaryoteseukaryotesTemplateStrand RNA sequence complementary to 1 DNA strandRNA Synthesis 1 Association of polymerase with DNA template DNA site where RNA polymerase binds to is promoter Additional proteins called transcription factorsHelp RNA polymerase recognize promoter 11RNA polymerase move in 35 directionDNA unwinds assembles complementary RNA strandRNA NTPRNAPP NTPRibonucleoside trisphosphate substratesnnInd2 reactionPPNP catalyzed by pyrophosphatase hydrolyze to inorganic I Iphosphate to make energy 2 Incorporate complementary nucleotides in NRNA chain only if able to form proper base pair 3 When polymerase move past certain part of DNAdouble helix reforms RNA chain doesnt associated w template as DNARNA hybrid 4 RNA polymerase needs to remain attached over long stretches of template processive but loose enough so it can move form nucleotide to the nextTranscription in BacteriaBacteria have 1 type of RNA polymerase 5 subunits to make core enzymesRNA polymerase formed by purified polymeraseIf purified accessory polypeptide called sigma factors added to RNA polymerase transcription begins at selected locationsincreases enzymes affinity for promoter sitesEnzymes separates to 2 DNA strandsStrand separation makes template strandOnce 1012 nucleotides incorporated enzymes undergoes major change in conformation and transformed to transcriptional elongation complexBacterial promotes at region of DNA before imitation site of RNA synthesis 1 UpstreamPortions before initiation site to 3 Downstream 1portions succeed it to 5
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