AP Bio Outline - Chapter 17 - Ginamarie Giacoio 10 2016...

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Ginamarie Giacoio November 10, 2016 Period 4 Chapter 17: Gene Expression: From Gene to Protein Concept 17.1 Genes specify proteins via transcription and translation Archibald Garrod was the first to suggest that genes dictate phenotypes through enzymes that catalyze specific chemical reactions in the cell. “Inborn errors of metabolism” refers to a person’s inability to make an enzyme, an example being alkaptonuria , a disorder where the urine is black because it contains the chemical alkapton, which cannot be metabolized in the cases of the people affected by it. Beadle and Edward Tatum demonstrated the relationship between genes and enzymes by using a break mold, Neurospora crassa, in which they caused genetic changed through X-rays, then looked among the survivors for mutants that differed their nutritional needs from the wild-type bread mold. o The results suggested that each class was blocked at a different step in this pathway because mutants in that class lacked the enzyme that catalyzed the blocked step. - One gene-one enzyme hypothesis. Not all proteins are enzymes, examples are Keratin, and the hormone insulin. A gene does not build a protein directly, the bridge between DNA and protein synthesis is the nucleic acid RNA. RNA is chemically similar to DNA except that it contains ribose instead of deoxyribose as its sugar and has the nitrogenous base uracil rather than thymine, and an RNA molecule usually being single strand rather than a double helix. Nucleic acids and proteins contain information written in two different chemical languages, and getting from DNA to protein requires two major stages, transcription and translation . Transcription : the synthesis of RNA using information in the DNA, the two nucleic acids are written in different forms of the same language, and the information is simply transcribed, or “rewritten”, from DNA to RNA Translation : the synthesis of a polypeptide using the information in the mRNA, there is a change in language: The cell must translate the nucleotide sequence of an mRNA (messenger RNA) molecule into the amino acid sequence of a polypeptide – the side of translation are RIBOSOMES
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There is an important difference in the flow of genetic information within the cells when it comes to the mechanics of transcription and translation for bacteria and eukaryotes. o Because bacteria do not have nuclei, their DNA is not separated by nuclear membranes from ribosomes and other protein-synthesizing equipment, the lack of compartmentalization allows translation of an mRNA to begin while its transcription is still in progress. o In contrast, the eukaryotic cell is separates transcription from translation in space and time. The initial RNA transcript from any gene, including those specifying RNA that is not translated into protein, is more generally called a primary transcript .
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