Bio_lecture_Nov2

Bio_lecture_Nov2 - 14 From DNA to Protein: Gene Expression...

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1 4 From DNA to Protein: Gene Expression
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From DNA to Protein: Gene Expression What Is the Evidence that Genes Code for Proteins? How Does Information Flow from Genes to Proteins? How Is the Information Content in DNA Transcribed to Produce RNA? How Is Eukaryotic DNA Transcribed and RNA Processed? How Is RNA Translated into Proteins? What Happens to Polypeptides after Translation?
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What Is the Evidence that Genes Code for Proteins? The molecular basis of phenotypes was discovered before it was known that DNA is the genetic material. Studies of many different organisms showed that major phenotypic differences were due to differences in specific proteins.
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What Is the Evidence that Genes Code for Proteins? Identification of a gene product as a protein began with a mutation. Garrod saw a disease phenotype— alkaptonuria—occurring in children who shared more alleles as first cousins. A substance in their blood (HA) accumulated—was not catalyzed—the gene for the enzyme was mutated. Garrod correlated one gene to one enzyme.
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What Is the Evidence that Genes Code for Proteins? Model organisms : Easy to grow or observe; show the phenomenon to be studied. Can assume that results from one organism can be applied to others. Examples: Pea plants; Drosophila ; E. coli ; common bread mold, Neurospora crassa.
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What Is the Evidence that Genes Code for Proteins? Beadle and Tatum used Neurospora to test hypothesis that specific gene expression specific enzyme activity. Neurospora is haploid for most of its life cycle—all alleles are expressed as phenotypes. • Minimum requirements for growth are carbon source (sugar), inorganic salts, and biotin Has enzymes to synthesize other molecules it needs
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What Is the Evidence that Genes Code for Proteins? Beadle and Tatum used X rays as mutagens to cause mutations— inherited genotypic changes. Mutants were auxotrophs —needed additional nutrients to grow. For each auxotrophic mutant strain, the addition of just one compound supported growth.
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What Is the Evidence that Genes Code for Proteins? Isolated several mutants requiring arginine for growth Examined for ability to grow in the presence of precursors 3 groups based on requirements Beadle and Tatum conclude that single gene controls the synthesis of a single enzyme – One gene – one enzyme hypothesis
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One Gene, One Enzyme (Part 2)
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What Is the Evidence that Genes Code for Proteins? Results suggested that each mutation caused a defect in only one enzyme in a metabolic pathway. This confirmed Garrod’s one-gene, one- enzyme hypothesis .
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What Is the Evidence that Genes Code for Proteins? The gene-enzyme relationship has since been revised to the one-gene, one- polypeptide relationship . Example: In hemoglobin, each polypeptide
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Bio_lecture_Nov2 - 14 From DNA to Protein: Gene Expression...

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