Ch12-From DNA to Protein

Ch12-From DNA to Protein - 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. The major phenotypic differences between organisms were due to specific 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. 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 Beadle and Tatum found several different arg mutant strains - had to be supplied with arginine. - could have mutations in the same gene; or in different genes in a biosynthetic pathway. - were grown in the presence of intermediates in the biosynthetic pathway for arginine. 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) RNA can pair with a single strand of DNA, except that adenine pairs with uracil instead of thymine. Single-strand RNA can fold into complex shapes by internal base pairing.
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12.2 How Does Information Flow from Genes to Proteins? The central dogma of molecular biology “Information flows in one direction when genes are expressed” (F.Crick). Raised two questions:
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This note was uploaded on 04/09/2008 for the course BIO 140 taught by Professor Morvaridsoltani-bejnood during the Spring '08 term at University of Tennessee.

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Ch12-From DNA to Protein - 12 From DNA to Protein: Genotype...

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