LECTURE 14 BILD1 S10

LECTURE 14 BILD1 S10 - Announcements Holiday Schedule...

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1 Announcements Holiday Schedule Monday, May 31st! No class, sections or office hours. Please see website for make-up Section times. Office Hours, TA Arek this Friday, May 21 , 10-11 AM, PC Foyer Office Hours, TA Thao Wednesday, June 2 , 12-1 PM, Café Roma Section A01, TA Patricia TBD Section A02, TA Arek Friday, May 28 , 10-11 AM, PC Foyer Lecture 14 From Genes to Proteins: Transcription & Translation From Genes to Proteins The Flow of Genetic Information The information content of DNA is in the form of specific sequences of nucleotides along the strands. DNA dictates protein synthesis ( gene expression ) in two major stages: 1. Transcription 2. Translation Genes Specify Proteins: Evidence from Metabolic Defects Archibald Garrod (1909) Suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions Beadle and Tatum Used X-rays to mutate bread mold, creating genetic mutants that could not survive on minimal medium…
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2 Mutants in Different Genes Required for Arginine Biosynthesis Three classes of mutants that could grow only with the addition of three different arginine intermediates Figure 17.2 Class I Mutants Class II Mutants Class III Mutants Wild type Minimal medium (MM) (control) MM + Ornithine MM + Citrulline MM + Arginine (control) Growth! Growth! Growth! Growth! No Growth No Growth No Growth Growth! No Growth Growth! No Growth Different Genes Responsible for Production of Specific Enzymes Class I Mutants (mutation in gene A ) Class II Mutants (mutation in gene B ) Class III Mutants (mutation in gene C ) Wild type Gene A Gene B Gene C Precursor Precursor Precursor Precursor Ornithine Ornithine Ornithine Ornithine Citrulline Citrulline Citrulline Citrulline Arginine Arginine Arginine Arginine Enzyme A Enzyme B Enzyme C A A A B B B C C C Mutants only grew if provided with the intermediates normally formed after the step when (mutated) enzyme functions “One Gene One Enzyme” Beadle and Tatum Hypothesized that the function of a gene is to dictate the production of a specific enzyme.* *or protein, polypeptide, RNA… Two Steps of Gene Expression 1. RNA Transcription the synthesis of RNA under the direction of DNA – Produces messenger RNA (mRNA) Occurs in the nucleus (1.5 RNA Processing…) 2. Protein Translation synthesis of a polypeptide under direction of mRNA Occurs on ribosomes
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3 Prokaryotes Eukaryotes Figure 17.3a TRANSLATION TRANSCRIPTION DNA mRNA Ribosome Polypeptide The Central Dogma: DNA RNA Protein Without nucleus, simultaneous transcription and translation TRANSCRIPTION RNA PROCESSING TRANSLATION mRNA DNA Pre-mRNA Polypeptide Ribosome Nuclear envelope With nucleus, transcription and translation separated and requires RNA processing transcription translation The Genetic Code How do nucleic acids correspond to an amino acid ?
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