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[BIO 1306] Ch12_Lecture

[BIO 1306] Ch12_Lecture - 12 From DNA to Protein Genotype...

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12 From DNA to Protein: Genotype to Phenotype
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12 From DNA to Protein: Genotype to Phenotype 12.1 What Is the Evidence that Genes Code for Proteins? 12.2 How Does Information Flow from Genes to Proteins? 12.3 How Is the Information Content in DNA Transcribed to Produce RNA? 12.4 How Is RNA Translated into Proteins? 12.5 What Happens to Polypeptides after Translation? 12.6 What Are Mutations?
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12.1 What Is the Evidence that Genes Code for Proteins? The molecular basis of phenotypes was known before it was known that DNA is the genetic material. Studies of many different organisms showed that major phenotypic differences were due to specific proteins.
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12.1 What Is the Evidence that Genes Code for Proteins? Model organisms : easy to grow or observe; show the phenomenon to be studied 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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12.1 What Is the Evidence that Genes Code for Proteins? Neurospora is haploid for most of its life cycle. Wild-type strains have enzymes to catalyze all reactions needed to make cell constituents— prototrophs . Beadle and Tatum used X-rays as mutagens . Mutants were auxotrophs needed additional nutrients to grow.
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12.1 What Is the Evidence that Genes Code for Proteins? For each auxotrophic strain, they found a single compound that would support growth of that strain. Suggested the one-gene, one-enzyme hypothesis
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Figure 12.1 One Gene, One Enzyme (Part 1)
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Figure 12.1 One Gene, One Enzyme (Part 2)
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12.1 What Is the Evidence that Genes Code for Proteins? Beadle and Tatum found several different arg mutant strains—had to be supplied with arginine. arg mutants could have mutations in the same gene; or in different genes that governed steps of a biosynthetic pathway.
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12.1 What Is the Evidence that Genes Code for Proteins? arg mutants were grown in the presence of compounds suspected to be intermediates in the biosynthetic pathway for arginine. This confirmed that each mutant was missing a single enzyme in the pathway.
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12.1 What Is the Evidence that Genes Code for Proteins? The gene-enzyme relationship has been revised to the one-gene, one-polypeptide relationship . Example: In hemoglobin, each polypeptide chain is specified by a separate gene. Other genes code for RNA that is not translated to polypeptides; some genes are involved in controlling other genes.
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12.2 How Does Information Flow from Genes to Proteins? Expression of a gene to form a polypeptide: Transcription —copies information from gene to a sequence of RNA. Translation —converts RNA sequence to amino acid sequence.
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12.2 How Does Information Flow from Genes to Proteins? RNA, ribonucleic acid differs from DNA: Usually one strand The sugar is ribose Contains uracil (U) instead of thymine (T)
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12.2 How Does Information Flow from Genes to Proteins?
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