RNAProtein211 - Genetic Code RNA and Protein Synthesis 1 As...

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Genetic Code, RNA and Protein Synthesis - 1 As we've discussed, the structure of DNA provides a mechanism for self- replication. DNA also "stores" the genetic information that determines what a cell is and how it functions. In this section, we will look at how the information stored in DNA is used to direct the synthesis of proteins (specifically polypeptides) through the processes of transcription and translation. Ultimately, the specific proteins in a cell determine the expressed phenotype. In a later section we will look at some of the ways in which gene expression is regulated so that the appropriate DNA is expressed in each cell. Before we discuss how DNA does its job of storing and using genetic information, let's look at some of the research that led to the conclusion that a gene is a piece of DNA that specifies the amino acid sequence in a polypeptide (or protein). Garrod's contribution In 1909 Archibald Garrod postulated that inherited diseases were caused by the inability of the individual to synthesize a particular enzyme as a result of a mutant allele. Garrod was the first to correlate "one gene to one enzyme". He was correct; many of our metabolic disorders are caused by not having a specific enzyme. However, it took decades of research to "prove" that a gene's function is to provide instructions on how to synthesize a specific protein, and that metabolic pathways for synthesis and degradation of molecules within a cell (and organism) are catalyzed by specific enzymes at each step of the pathway. Beadle, Ephrussi, Tatum, Drosophila eye color and Pink Bread Mold In the 1930's, George Beadle and Boris Ephrussi postulated that the variations in eye color were caused by mutations in the enzymes that catalyzed eye pigment, but were not able to identify the chemical pathway of the enzymes. A decade later Beadle and Edward Tatum induced mutations in Neurospora , a common pink mold, and tracked the nutrient metabolism of the mutant strains. Neurospora has a haploid life cycle so each individual has just one allele for each genetic trait.
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Genetic Code, RNA and Protein Synthesis - 2 They mapped chromosome locations of the mutant strains, and then related their chromosome maps to the presence or absence of specific enzymes needed in Neurospora 's metabolic pathway for the synthesis of arginine. They compared the wild type (prototroph) that could synthesize its nutrients from a minimal nutrient medium with several different auxotrophs (the mutant forms that could not survive on the minimal medium). From their research, Beadle and Tatum postulated the one gene-one enzyme theory. Eventually, we also learned that not all genes must code for enzymes; some code for structural proteins or functional proteins (many of which we discussed in our first unit). Furthermore, quaternary proteins are composed of more than one polypeptide, so the concept of gene was further refined to be that a gene codes for a polypeptide. Continued research found that some genes code for the many forms of RNA found
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RNAProtein211 - Genetic Code RNA and Protein Synthesis 1 As...

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