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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Fig. 9-1Chapter 9: Proteins and their synthesisCoupled transcription/translation Compartmentedtranscription/processing/translationFig. 9-2Proteins are polymers of amino acids joined through peptide bondsEach protein has a amino- and a carboxyl-terminusThe function of a protein is dependent upon its overall structure; each level of protein structure is dependentupon lower levels; thus, all are derivatives of primary structure of the polypeptideThe primary structures of polypeptides are directly derived from the primary structures of their mRNAsPrimary structures of mRNA are derived from the primary structures of their DNA templates (± splicing)Changes in DNA sequence can alter function of proteins encoded by that DNA sequenceFig. 9-3Protein higher order structuresamino acid sequenceRegular coil/sheet motifs stabilized by H-bonds between peptidyl atomsspecific intramolecular folding stabilized by associations of amino acid “R” groupsintermolecular associations stabilized by associations of amino acid “R” groupsTertiary and quaternary structures are determined by primary structureFig. 9-4Fig. 9-5Genes encode the primary structure of proteinsE. coli trpA mutations: genetic map is co-linear with the protein(C. Yanofsky)Fig. 9-8Degeneracy in the codon-amino acid code derives from:• Multiple codons for certain same amino acidse.g., UCUUCCUCA serineUCGUGUUGCFig. 9-10tRNAs convert the codon-amino acid codemediated by aminoacyl synthetasesDegeneracy in the codon-amino acid code derives from:• Multiple codons for certain same amino acidse.g., UCUUCCUCA serineUCGUGUUGC• “Wobble” permits certain individual tRNAs to pair with multiple codonsFig. 9-12“Wobble” creates partial ambiguity in codon 3’ nucleotidesFig. 9-15Three significant domains of ribosome during translation:A: incoming aminoacyl-tRNA binding siteP: peptidyl-tRNA binding siteE: exiting deacylated-tRNA siteFig. 9-18Three phases of translation:Initiation: • association of small subunit and capped 5’ end of mRNA• association of Met-tRNA (fMet)• scanning to AUG (eukaryotes)• association of large subunitThree phases of translation:InitiationElongation• aa-tRNA association with A site• transfer of peptidyl to aa-tRNA• translocation (next codon)• exiting of deacylated tRNAFig. 9-19Three phases of translation:InitiationElongationTermination• stop codon recruits release factor• hydrolysis of peptidyl-tRNA link• release of complexFig. 9-21Translational suppressors:mutant tRNAs with modified anticodons that permit “readthrough” of nonsense mutationsFig. 9-23Posttranslational modifications of proteins:• protein folding into “native” configuration (assisted by chaperones)• covalent modifications of amino acid side chains• targetting to specific intra- and extracellular sitesAll subject to mutation in the protein or in the cellular machinery that modifies the proteinFig.


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UK BIO 304 - Lecture 8

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