Proteins, Proteins, Proteins!

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What is the connection between genes (DNA) & phenotype? IOW, how, exactly, do genes determine who we are?. Proteins, Proteins, Proteins! Many are structural in nature, but most traits are determined by enzymes (or lack thereof!) Transcription & translation link genes to proteins - PowerPoint PPT Presentation

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  • What is the connection between genes (DNA) & phenotype?IOW, how, exactly, do genes determine who we are?Proteins, Proteins, Proteins!Many are structural in nature, but most traits are determined by enzymes (or lack thereof!)Transcription & translation link genes to proteinsDNA RNA protein transcription translation

  • One gene, one-enzyme hypothesis

    Proposed by Garod, 1909Confirmed by Beadle & Tatum, 1930Worked w/ neurospora (bread mold) mutantsModified to one gene, one polypeptide

  • Overview

  • The Triplet Code

    3 bases on DNA specify a particular amino acidA gene contains enough triplet codes to specify a particular polypeptide chain,along with regulatory DNA

  • The genetic codeRefers specifically to mRNA codonsComplementary to DNA tripletsUniversalDegenerateWobble

    DNA- CCA/GGT/TTT/CGA RNA- GGU/CCA/AAA/GCUAminos - gly/pro/lys/ala

  • DNA- CCA/GGT/TTT/CGAm RNA- GGU/CCA/AAA/GCUtRNA- CCA/GGU/UUU/CGAAminos - gly/ pro/ lys/ ala

    Aminos - gly/pro/lys/ala

  • Transcription-mRNA synthesis3 stages-initiation, elongation, terminationCatalyzed by RNA polymerase(synthesizes 5 3)DNA is organized into Transcription units (genes)Initiation sequence, triplet codes for polypeptide, terminationPer gene, only one strand of DNA is transcribed(template, anti-sense)Which strand may vary from gene to gene

  • initiationRNA pol binds to promoterPromoter includes binding site & initiation siteRNA pol unzips DNA & begins Putting Complementary bases in place

  • elongationNew strand is built in 3 to 5 directionUracil instead of thymineUses nucleoside triphosphates

  • terminationTerminator sequence (DNA)Signals end of polypeptideRNA pol dissociates, DNA zips up, mRNA released

  • Eukaryotes vs prokaryotesIn nucleusPromoter includes the TATA box (for transcription factors)Transcription units only contain info for1 polypeptide chainmRNA must be processed before translationIn cytoplasmNo TATA box or transcription factorsTranscription units may contain info for several different polypeptide chains, but have 1 set of regulatorsNo mRNA processingTranslation can take place simultaneously w/ transcription

  • RNA processingMethylguanosine cap added to 5endProtection,Ribosomal attachmentPoly-A tail added to 3 endProtection,Transport to cytoplasmINTRONS (intervening sequences) cut outEXONS left & spliced togetherSpliceosomes-proteins (enzymes) & RNAAlternative RNA processing

  • RNAi (interference)Post-transcriptional gene silencingShort Double-stranded RNA (siRNA) triggers degradation of homologous mRNAMay be protective (proofreading)research

  • The Anti-Codon

    Complementary to codonsFound on tRNAcloverleaf shapeAttachment site for amino acidAnti codon at opposite end1 tRNA per amino acidAminoacyl tRNA synthetaseInosine (U,C, or A)