Gene Expression Tsquare

Gene Expression Tsquare - Gene Expression From Gene to...

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Gene Expression From Gene to Protein: Transcription and translation
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The DNA inherited by an organism Leads to specific traits by dictating the synthesis of proteins The process by which DNA directs protein synthesis, gene expression Includes two stages, called transcription and translation
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Evidence from the Study of Metabolic Defects In 1909, British physician Archibald Garrod Was the first to suggest that genes dictate phenotypes through enzymes that catalyze specific chemical reactions in the cell
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Nutritional Mutants in Neurospora: Scientific Inquiry Beadle and Tatum causes bread mold to mutate with X-rays Creating mutants that could not survive on minimal medium
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CONCLUSION From the growth patterns of the mutants, Beadle and Tatum deduced that each mutant was unable to carry out one step in the pathway for synthesizing arginine, presumably because it lacked the necessary enzyme. Because each of their mutants was mutated in a single gene, they concluded that each mutated gene must normally dictate the production of one enzyme. Their results supported the one gene–one enzyme hypothesis and also confirmed the arginine pathway. (Notice that a mutant can grow only if supplied with a compound made after the defective step.) 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
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Beadle and Tatum developed the “one gene–one enzyme hypothesis” Which states that the function of a gene is to dictate the production of a specific enzyme
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The Products of Gene Expression: A Developing Story As researchers learned more about proteins The made minor revision to the one gene–one enzyme hypothesis Genes code for polypeptide chains or for RNA molecules
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Basic Principles of Transcription and Translation Transcription Is the synthesis of RNA under the direction of DNA Produces messenger RNA (mRNA) Translation Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA Occurs on ribosomes
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In prokaryotes Transcription and translation occur together Figure 17.3a Prokaryotic cell. In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing. (a) TRANSLATION TRANSCRIPTION DNA mRNA Ribosome Polypeptide
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In eukaryotes RNA transcripts are modified before becoming true mRNA Figure 17.3b Eukaryotic cell. The nucleus provides a separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. (b)
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This note was uploaded on 04/07/2008 for the course BIO 1510 taught by Professor Unknown during the Fall '07 term at Georgia Tech.

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Gene Expression Tsquare - Gene Expression From Gene to...

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